Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3007 insertions, 0 deletions

diff --git a/layout/generic/nsFloatManager.cpp b/layout/generic/nsFloatManager.cpp
new file mode 100644
index 0000000000..ec2ff0ac4a
--- /dev/null
+++ b/layout/generic/nsFloatManager.cpp
@@ -0,0 +1,3007 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* class that manages rules for positioning floats */
+
+#include "nsFloatManager.h"
+
+#include <algorithm>
+#include <initializer_list>
+
+#include "gfxContext.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/ReflowInput.h"
+#include "mozilla/ShapeUtils.h"
+#include "nsBlockFrame.h"
+#include "nsDeviceContext.h"
+#include "nsError.h"
+#include "nsIFrame.h"
+#include "nsIFrameInlines.h"
+#include "nsImageRenderer.h"
+
+using namespace mozilla;
+using namespace mozilla::image;
+using namespace mozilla::gfx;
+
+int32_t nsFloatManager::sCachedFloatManagerCount = 0;
+void* nsFloatManager::sCachedFloatManagers[NS_FLOAT_MANAGER_CACHE_SIZE];
+
+/////////////////////////////////////////////////////////////////////////////
+// nsFloatManager
+
+nsFloatManager::nsFloatManager(PresShell* aPresShell, WritingMode aWM)
+    :
+#ifdef DEBUG
+      mWritingMode(aWM),
+#endif
+      mLineLeft(0),
+      mBlockStart(0),
+      mFloatDamage(aPresShell),
+      mPushedLeftFloatPastBreak(false),
+      mPushedRightFloatPastBreak(false),
+      mSplitLeftFloatAcrossBreak(false),
+      mSplitRightFloatAcrossBreak(false) {
+  MOZ_COUNT_CTOR(nsFloatManager);
+}
+
+nsFloatManager::~nsFloatManager() { MOZ_COUNT_DTOR(nsFloatManager); }
+
+// static
+void* nsFloatManager::operator new(size_t aSize) noexcept(true) {
+  if (sCachedFloatManagerCount > 0) {
+    // We have cached unused instances of this class, return a cached
+    // instance in stead of always creating a new one.
+    return sCachedFloatManagers[--sCachedFloatManagerCount];
+  }
+
+  // The cache is empty, this means we have to create a new instance using
+  // the global |operator new|.
+  return moz_xmalloc(aSize);
+}
+
+void nsFloatManager::operator delete(void* aPtr, size_t aSize) {
+  if (!aPtr) return;
+  // This float manager is no longer used, if there's still room in
+  // the cache we'll cache this float manager, unless the layout
+  // module was already shut down.
+
+  if (sCachedFloatManagerCount < NS_FLOAT_MANAGER_CACHE_SIZE &&
+      sCachedFloatManagerCount >= 0) {
+    // There's still space in the cache for more instances, put this
+    // instance in the cache in stead of deleting it.
+
+    sCachedFloatManagers[sCachedFloatManagerCount++] = aPtr;
+    return;
+  }
+
+  // The cache is full, or the layout module has been shut down,
+  // delete this float manager.
+  free(aPtr);
+}
+
+/* static */
+void nsFloatManager::Shutdown() {
+  // The layout module is being shut down, clean up the cache and
+  // disable further caching.
+
+  int32_t i;
+
+  for (i = 0; i < sCachedFloatManagerCount; i++) {
+    void* floatManager = sCachedFloatManagers[i];
+    if (floatManager) free(floatManager);
+  }
+
+  // Disable further caching.
+  sCachedFloatManagerCount = -1;
+}
+
+#define CHECK_BLOCK_AND_LINE_DIR(aWM)                                       \
+  NS_ASSERTION((aWM).GetBlockDir() == mWritingMode.GetBlockDir() &&         \
+                   (aWM).IsLineInverted() == mWritingMode.IsLineInverted(), \
+               "incompatible writing modes")
+
+nsFlowAreaRect nsFloatManager::GetFlowArea(
+    WritingMode aWM, nscoord aBCoord, nscoord aBSize,
+    BandInfoType aBandInfoType, ShapeType aShapeType, LogicalRect aContentArea,
+    SavedState* aState, const nsSize& aContainerSize) const {
+  CHECK_BLOCK_AND_LINE_DIR(aWM);
+  NS_ASSERTION(aBSize >= 0, "unexpected max block size");
+  NS_ASSERTION(aContentArea.ISize(aWM) >= 0,
+               "unexpected content area inline size");
+
+  nscoord blockStart = aBCoord + mBlockStart;
+  if (blockStart < nscoord_MIN) {
+    NS_WARNING("bad value");
+    blockStart = nscoord_MIN;
+  }
+
+  // Determine the last float that we should consider.
+  uint32_t floatCount;
+  if (aState) {
+    // Use the provided state.
+    floatCount = aState->mFloatInfoCount;
+    MOZ_ASSERT(floatCount <= mFloats.Length(), "bad state");
+  } else {
+    // Use our current state.
+    floatCount = mFloats.Length();
+  }
+
+  // If there are no floats at all, or we're below the last one, return
+  // quickly.
+  if (floatCount == 0 || (mFloats[floatCount - 1].mLeftBEnd <= blockStart &&
+                          mFloats[floatCount - 1].mRightBEnd <= blockStart)) {
+    return nsFlowAreaRect(aWM, aContentArea.IStart(aWM), aBCoord,
+                          aContentArea.ISize(aWM), aBSize,
+                          nsFlowAreaRectFlags::NoFlags);
+  }
+
+  nscoord blockEnd;
+  if (aBSize == nscoord_MAX) {
+    // This warning (and the two below) are possible to hit on pages
+    // with really large objects.
+    NS_WARNING_ASSERTION(aBandInfoType == BandInfoType::BandFromPoint,
+                         "bad height");
+    blockEnd = nscoord_MAX;
+  } else {
+    blockEnd = blockStart + aBSize;
+    if (blockEnd < blockStart || blockEnd > nscoord_MAX) {
+      NS_WARNING("bad value");
+      blockEnd = nscoord_MAX;
+    }
+  }
+  nscoord lineLeft = mLineLeft + aContentArea.LineLeft(aWM, aContainerSize);
+  nscoord lineRight = mLineLeft + aContentArea.LineRight(aWM, aContainerSize);
+  if (lineRight < lineLeft) {
+    NS_WARNING("bad value");
+    lineRight = lineLeft;
+  }
+
+  // Walk backwards through the floats until we either hit the front of
+  // the list or we're above |blockStart|.
+  bool haveFloats = false;
+  bool mayWiden = false;
+  for (uint32_t i = floatCount; i > 0; --i) {
+    const FloatInfo& fi = mFloats[i - 1];
+    if (fi.mLeftBEnd <= blockStart && fi.mRightBEnd <= blockStart) {
+      // There aren't any more floats that could intersect this band.
+      break;
+    }
+    if (fi.IsEmpty(aShapeType)) {
+      // Ignore empty float areas.
+      // https://drafts.csswg.org/css-shapes/#relation-to-box-model-and-float-behavior
+      continue;
+    }
+
+    nscoord floatBStart = fi.BStart(aShapeType);
+    nscoord floatBEnd = fi.BEnd(aShapeType);
+    if (blockStart < floatBStart &&
+        aBandInfoType == BandInfoType::BandFromPoint) {
+      // This float is below our band.  Shrink our band's height if needed.
+      if (floatBStart < blockEnd) {
+        blockEnd = floatBStart;
+      }
+    }
+    // If blockStart == blockEnd (which happens only with WidthWithinHeight),
+    // we include floats that begin at our 0-height vertical area.  We
+    // need to do this to satisfy the invariant that a
+    // WidthWithinHeight call is at least as narrow on both sides as a
+    // BandFromPoint call beginning at its blockStart.
+    else if (blockStart < floatBEnd &&
+             (floatBStart < blockEnd ||
+              (floatBStart == blockEnd && blockStart == blockEnd))) {
+      // This float is in our band.
+
+      // Shrink our band's width if needed.
+      StyleFloat floatStyle = fi.mFrame->StyleDisplay()->mFloat;
+
+      // When aBandInfoType is BandFromPoint, we're only intended to
+      // consider a point along the y axis rather than a band.
+      const nscoord bandBlockEnd =
+          aBandInfoType == BandInfoType::BandFromPoint ? blockStart : blockEnd;
+      if (floatStyle == StyleFloat::Left) {
+        // A left float
+        nscoord lineRightEdge =
+            fi.LineRight(aShapeType, blockStart, bandBlockEnd);
+        if (lineRightEdge > lineLeft) {
+          lineLeft = lineRightEdge;
+          // Only set haveFloats to true if the float is inside our
+          // containing block.  This matches the spec for what some
+          // callers want and disagrees for other callers, so we should
+          // probably provide better information at some point.
+          haveFloats = true;
+
+          // Our area may widen in the block direction if this float may
+          // narrow in the block direction.
+          mayWiden = mayWiden || fi.MayNarrowInBlockDirection(aShapeType);
+        }
+      } else {
+        // A right float
+        nscoord lineLeftEdge =
+            fi.LineLeft(aShapeType, blockStart, bandBlockEnd);
+        if (lineLeftEdge < lineRight) {
+          lineRight = lineLeftEdge;
+          // See above.
+          haveFloats = true;
+          mayWiden = mayWiden || fi.MayNarrowInBlockDirection(aShapeType);
+        }
+      }
+
+      // Shrink our band's height if needed.
+      if (floatBEnd < blockEnd &&
+          aBandInfoType == BandInfoType::BandFromPoint) {
+        blockEnd = floatBEnd;
+      }
+    }
+  }
+
+  nscoord blockSize =
+      (blockEnd == nscoord_MAX) ? nscoord_MAX : (blockEnd - blockStart);
+  // convert back from LineLeft/Right to IStart
+  nscoord inlineStart =
+      aWM.IsBidiLTR()
+          ? lineLeft - mLineLeft
+          : mLineLeft - lineRight + LogicalSize(aWM, aContainerSize).ISize(aWM);
+
+  nsFlowAreaRectFlags flags =
+      (haveFloats ? nsFlowAreaRectFlags::HasFloats
+                  : nsFlowAreaRectFlags::NoFlags) |
+      (mayWiden ? nsFlowAreaRectFlags::MayWiden : nsFlowAreaRectFlags::NoFlags);
+  // Some callers clamp the inline size of nsFlowAreaRect to be nonnegative
+  // "for compatibility with nsSpaceManager". So, we set a flag here to record
+  // the fact that the ISize is actually negative, so that downstream code can
+  // realize that there's no place here where we could put a float-avoiding
+  // block (even one with ISize of 0).
+  if (lineRight - lineLeft < 0) {
+    flags |= nsFlowAreaRectFlags::ISizeIsActuallyNegative;
+  }
+
+  return nsFlowAreaRect(aWM, inlineStart, blockStart - mBlockStart,
+                        lineRight - lineLeft, blockSize, flags);
+}
+
+void nsFloatManager::AddFloat(nsIFrame* aFloatFrame,
+                              const LogicalRect& aMarginRect, WritingMode aWM,
+                              const nsSize& aContainerSize) {
+  CHECK_BLOCK_AND_LINE_DIR(aWM);
+  NS_ASSERTION(aMarginRect.ISize(aWM) >= 0, "negative inline size!");
+  NS_ASSERTION(aMarginRect.BSize(aWM) >= 0, "negative block size!");
+
+  FloatInfo info(aFloatFrame, mLineLeft, mBlockStart, aMarginRect, aWM,
+                 aContainerSize);
+
+  // Set mLeftBEnd and mRightBEnd.
+  if (HasAnyFloats()) {
+    FloatInfo& tail = mFloats[mFloats.Length() - 1];
+    info.mLeftBEnd = tail.mLeftBEnd;
+    info.mRightBEnd = tail.mRightBEnd;
+  } else {
+    info.mLeftBEnd = nscoord_MIN;
+    info.mRightBEnd = nscoord_MIN;
+  }
+  StyleFloat floatStyle = aFloatFrame->StyleDisplay()->mFloat;
+  MOZ_ASSERT(floatStyle == StyleFloat::Left || floatStyle == StyleFloat::Right,
+             "Unexpected float style!");
+  nscoord& sideBEnd =
+      floatStyle == StyleFloat::Left ? info.mLeftBEnd : info.mRightBEnd;
+  nscoord thisBEnd = info.BEnd();
+  if (thisBEnd > sideBEnd) sideBEnd = thisBEnd;
+
+  mFloats.AppendElement(std::move(info));
+}
+
+// static
+LogicalRect nsFloatManager::CalculateRegionFor(WritingMode aWM,
+                                               nsIFrame* aFloat,
+                                               const LogicalMargin& aMargin,
+                                               const nsSize& aContainerSize) {
+  // We consider relatively positioned frames at their original position.
+  LogicalRect region(aWM,
+                     nsRect(aFloat->GetNormalPosition(), aFloat->GetSize()),
+                     aContainerSize);
+
+  // Float region includes its margin
+  region.Inflate(aWM, aMargin);
+
+  // Don't store rectangles with negative margin-box width or height in
+  // the float manager; it can't deal with them.
+  if (region.ISize(aWM) < 0) {
+    // Preserve the right margin-edge for left floats and the left
+    // margin-edge for right floats
+    const nsStyleDisplay* display = aFloat->StyleDisplay();
+    StyleFloat floatStyle = display->mFloat;
+    if ((StyleFloat::Left == floatStyle) == aWM.IsBidiLTR()) {
+      region.IStart(aWM) = region.IEnd(aWM);
+    }
+    region.ISize(aWM) = 0;
+  }
+  if (region.BSize(aWM) < 0) {
+    region.BSize(aWM) = 0;
+  }
+  return region;
+}
+
+NS_DECLARE_FRAME_PROPERTY_DELETABLE(FloatRegionProperty, nsMargin)
+
+LogicalRect nsFloatManager::GetRegionFor(WritingMode aWM, nsIFrame* aFloat,
+                                         const nsSize& aContainerSize) {
+  LogicalRect region = aFloat->GetLogicalRect(aWM, aContainerSize);
+  void* storedRegion = aFloat->GetProperty(FloatRegionProperty());
+  if (storedRegion) {
+    nsMargin margin = *static_cast<nsMargin*>(storedRegion);
+    region.Inflate(aWM, LogicalMargin(aWM, margin));
+  }
+  return region;
+}
+
+void nsFloatManager::StoreRegionFor(WritingMode aWM, nsIFrame* aFloat,
+                                    const LogicalRect& aRegion,
+                                    const nsSize& aContainerSize) {
+  nsRect region = aRegion.GetPhysicalRect(aWM, aContainerSize);
+  nsRect rect = aFloat->GetRect();
+  if (region.IsEqualEdges(rect)) {
+    aFloat->RemoveProperty(FloatRegionProperty());
+  } else {
+    nsMargin* storedMargin = aFloat->GetProperty(FloatRegionProperty());
+    if (!storedMargin) {
+      storedMargin = new nsMargin();
+      aFloat->SetProperty(FloatRegionProperty(), storedMargin);
+    }
+    *storedMargin = region - rect;
+  }
+}
+
+nsresult nsFloatManager::RemoveTrailingRegions(nsIFrame* aFrameList) {
+  if (!aFrameList) {
+    return NS_OK;
+  }
+  // This could be a good bit simpler if we could guarantee that the
+  // floats given were at the end of our list, so we could just search
+  // for the head of aFrameList.  (But we can't;
+  // layout/reftests/bugs/421710-1.html crashes.)
+  nsTHashSet<nsIFrame*> frameSet(1);
+
+  for (nsIFrame* f = aFrameList; f; f = f->GetNextSibling()) {
+    frameSet.Insert(f);
+  }
+
+  uint32_t newLength = mFloats.Length();
+  while (newLength > 0) {
+    if (!frameSet.Contains(mFloats[newLength - 1].mFrame)) {
+      break;
+    }
+    --newLength;
+  }
+  mFloats.TruncateLength(newLength);
+
+#ifdef DEBUG
+  for (uint32_t i = 0; i < mFloats.Length(); ++i) {
+    NS_ASSERTION(
+        !frameSet.Contains(mFloats[i].mFrame),
+        "Frame region deletion was requested but we couldn't delete it");
+  }
+#endif
+
+  return NS_OK;
+}
+
+void nsFloatManager::PushState(SavedState* aState) {
+  MOZ_ASSERT(aState, "Need a place to save state");
+
+  // This is a cheap push implementation, which
+  // only saves the (x,y) and last frame in the mFrameInfoMap
+  // which is enough info to get us back to where we should be
+  // when pop is called.
+  //
+  // This push/pop mechanism is used to undo any
+  // floats that were added during the unconstrained reflow
+  // in nsBlockReflowContext::DoReflowBlock(). (See bug 96736)
+  //
+  // It should also be noted that the state for mFloatDamage is
+  // intentionally not saved or restored in PushState() and PopState(),
+  // since that could lead to bugs where damage is missed/dropped when
+  // we move from position A to B (during the intermediate incremental
+  // reflow mentioned above) and then from B to C during the subsequent
+  // reflow. In the typical case A and C will be the same, but not always.
+  // Allowing mFloatDamage to accumulate the damage incurred during both
+  // reflows ensures that nothing gets missed.
+  aState->mLineLeft = mLineLeft;
+  aState->mBlockStart = mBlockStart;
+  aState->mPushedLeftFloatPastBreak = mPushedLeftFloatPastBreak;
+  aState->mPushedRightFloatPastBreak = mPushedRightFloatPastBreak;
+  aState->mSplitLeftFloatAcrossBreak = mSplitLeftFloatAcrossBreak;
+  aState->mSplitRightFloatAcrossBreak = mSplitRightFloatAcrossBreak;
+  aState->mFloatInfoCount = mFloats.Length();
+}
+
+void nsFloatManager::PopState(SavedState* aState) {
+  MOZ_ASSERT(aState, "No state to restore?");
+
+  mLineLeft = aState->mLineLeft;
+  mBlockStart = aState->mBlockStart;
+  mPushedLeftFloatPastBreak = aState->mPushedLeftFloatPastBreak;
+  mPushedRightFloatPastBreak = aState->mPushedRightFloatPastBreak;
+  mSplitLeftFloatAcrossBreak = aState->mSplitLeftFloatAcrossBreak;
+  mSplitRightFloatAcrossBreak = aState->mSplitRightFloatAcrossBreak;
+
+  NS_ASSERTION(aState->mFloatInfoCount <= mFloats.Length(),
+               "somebody misused PushState/PopState");
+  mFloats.TruncateLength(aState->mFloatInfoCount);
+}
+
+nscoord nsFloatManager::LowestFloatBStart() const {
+  if (mPushedLeftFloatPastBreak || mPushedRightFloatPastBreak) {
+    return nscoord_MAX;
+  }
+  if (!HasAnyFloats()) {
+    return nscoord_MIN;
+  }
+  return mFloats[mFloats.Length() - 1].BStart() - mBlockStart;
+}
+
+#ifdef DEBUG_FRAME_DUMP
+void DebugListFloatManager(const nsFloatManager* aFloatManager) {
+  aFloatManager->List(stdout);
+}
+
+nsresult nsFloatManager::List(FILE* out) const {
+  if (!HasAnyFloats()) return NS_OK;
+
+  for (uint32_t i = 0; i < mFloats.Length(); ++i) {
+    const FloatInfo& fi = mFloats[i];
+    fprintf_stderr(out,
+                   "Float %u: frame=%p rect={%d,%d,%d,%d} BEnd={l:%d, r:%d}\n",
+                   i, static_cast<void*>(fi.mFrame), fi.LineLeft(), fi.BStart(),
+                   fi.ISize(), fi.BSize(), fi.mLeftBEnd, fi.mRightBEnd);
+  }
+  return NS_OK;
+}
+#endif
+
+nscoord nsFloatManager::ClearFloats(nscoord aBCoord,
+                                    StyleClear aClearType) const {
+  if (!HasAnyFloats()) {
+    return aBCoord;
+  }
+
+  nscoord blockEnd = aBCoord + mBlockStart;
+
+  const FloatInfo& tail = mFloats[mFloats.Length() - 1];
+  switch (aClearType) {
+    case StyleClear::Both:
+      blockEnd = std::max(blockEnd, tail.mLeftBEnd);
+      blockEnd = std::max(blockEnd, tail.mRightBEnd);
+      break;
+    case StyleClear::Left:
+      blockEnd = std::max(blockEnd, tail.mLeftBEnd);
+      break;
+    case StyleClear::Right:
+      blockEnd = std::max(blockEnd, tail.mRightBEnd);
+      break;
+    default:
+      // Do nothing
+      break;
+  }
+
+  blockEnd -= mBlockStart;
+
+  return blockEnd;
+}
+
+bool nsFloatManager::ClearContinues(StyleClear aClearType) const {
+  return ((mPushedLeftFloatPastBreak || mSplitLeftFloatAcrossBreak) &&
+          (aClearType == StyleClear::Both || aClearType == StyleClear::Left)) ||
+         ((mPushedRightFloatPastBreak || mSplitRightFloatAcrossBreak) &&
+          (aClearType == StyleClear::Both || aClearType == StyleClear::Right));
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// ShapeInfo is an abstract class for implementing all the shapes in CSS
+// Shapes Module. A subclass needs to override all the methods to adjust
+// the flow area with respect to its shape.
+//
+class nsFloatManager::ShapeInfo {
+ public:
+  virtual ~ShapeInfo() = default;
+
+  virtual nscoord LineLeft(const nscoord aBStart,
+                           const nscoord aBEnd) const = 0;
+  virtual nscoord LineRight(const nscoord aBStart,
+                            const nscoord aBEnd) const = 0;
+  virtual nscoord BStart() const = 0;
+  virtual nscoord BEnd() const = 0;
+  virtual bool IsEmpty() const = 0;
+
+  // Does this shape possibly get inline narrower in the BStart() to BEnd()
+  // span when proceeding in the block direction? This is false for unrounded
+  // rectangles that span all the way to BEnd(), but could be true for other
+  // shapes. Note that we don't care if the BEnd() falls short of the margin
+  // rect -- the ShapeInfo can only affect float behavior in the span between
+  // BStart() and BEnd().
+  virtual bool MayNarrowInBlockDirection() const = 0;
+
+  // Translate the current origin by the specified offsets.
+  virtual void Translate(nscoord aLineLeft, nscoord aBlockStart) = 0;
+
+  static LogicalRect ComputeShapeBoxRect(StyleShapeBox, nsIFrame* const aFrame,
+                                         const LogicalRect& aMarginRect,
+                                         WritingMode aWM);
+
+  // Convert the LogicalRect to the special logical coordinate space used
+  // in float manager.
+  static nsRect ConvertToFloatLogical(const LogicalRect& aRect, WritingMode aWM,
+                                      const nsSize& aContainerSize) {
+    return nsRect(aRect.LineLeft(aWM, aContainerSize), aRect.BStart(aWM),
+                  aRect.ISize(aWM), aRect.BSize(aWM));
+  }
+
+  static UniquePtr<ShapeInfo> CreateShapeBox(nsIFrame* const aFrame,
+                                             nscoord aShapeMargin,
+                                             const LogicalRect& aShapeBoxRect,
+                                             WritingMode aWM,
+                                             const nsSize& aContainerSize);
+
+  static UniquePtr<ShapeInfo> CreateBasicShape(
+      const StyleBasicShape& aBasicShape, nscoord aShapeMargin,
+      nsIFrame* const aFrame, const LogicalRect& aShapeBoxRect,
+      const LogicalRect& aMarginRect, WritingMode aWM,
+      const nsSize& aContainerSize);
+
+  static UniquePtr<ShapeInfo> CreateInset(const StyleBasicShape& aBasicShape,
+                                          nscoord aShapeMargin,
+                                          nsIFrame* aFrame,
+                                          const LogicalRect& aShapeBoxRect,
+                                          WritingMode aWM,
+                                          const nsSize& aContainerSize);
+
+  static UniquePtr<ShapeInfo> CreateCircleOrEllipse(
+      const StyleBasicShape& aBasicShape, nscoord aShapeMargin,
+      nsIFrame* const aFrame, const LogicalRect& aShapeBoxRect, WritingMode aWM,
+      const nsSize& aContainerSize);
+
+  static UniquePtr<ShapeInfo> CreatePolygon(const StyleBasicShape& aBasicShape,
+                                            nscoord aShapeMargin,
+                                            nsIFrame* const aFrame,
+                                            const LogicalRect& aShapeBoxRect,
+                                            const LogicalRect& aMarginRect,
+                                            WritingMode aWM,
+                                            const nsSize& aContainerSize);
+
+  static UniquePtr<ShapeInfo> CreateImageShape(const StyleImage& aShapeImage,
+                                               float aShapeImageThreshold,
+                                               nscoord aShapeMargin,
+                                               nsIFrame* const aFrame,
+                                               const LogicalRect& aMarginRect,
+                                               WritingMode aWM,
+                                               const nsSize& aContainerSize);
+
+ protected:
+  // Compute the minimum line-axis difference between the bounding shape
+  // box and its rounded corner within the given band (block-axis region).
+  // This is used as a helper function to compute the LineRight() and
+  // LineLeft(). See the picture in the implementation for an example.
+  // RadiusL and RadiusB stand for radius on the line-axis and block-axis.
+  //
+  // Returns radius-x diff on the line-axis, or 0 if there's no rounded
+  // corner within the given band.
+  static nscoord ComputeEllipseLineInterceptDiff(
+      const nscoord aShapeBoxBStart, const nscoord aShapeBoxBEnd,
+      const nscoord aBStartCornerRadiusL, const nscoord aBStartCornerRadiusB,
+      const nscoord aBEndCornerRadiusL, const nscoord aBEndCornerRadiusB,
+      const nscoord aBandBStart, const nscoord aBandBEnd);
+
+  static nscoord XInterceptAtY(const nscoord aY, const nscoord aRadiusX,
+                               const nscoord aRadiusY);
+
+  // Convert the physical point to the special logical coordinate space
+  // used in float manager.
+  static nsPoint ConvertToFloatLogical(const nsPoint& aPoint, WritingMode aWM,
+                                       const nsSize& aContainerSize);
+
+  // Convert the half corner radii (nscoord[8]) to the special logical
+  // coordinate space used in float manager.
+  static UniquePtr<nscoord[]> ConvertToFloatLogical(const nscoord aRadii[8],
+                                                    WritingMode aWM);
+
+  // Some ShapeInfo subclasses may define their float areas in intervals.
+  // Each interval is a rectangle that is one device pixel deep in the block
+  // axis. The values are stored as block edges in the y coordinates,
+  // and inline edges as the x coordinates. Interval arrays should be sorted
+  // on increasing y values. This function uses a binary search to find the
+  // first interval that contains aTargetY. If no such interval exists, this
+  // function returns aIntervals.Length().
+  static size_t MinIntervalIndexContainingY(const nsTArray<nsRect>& aIntervals,
+                                            const nscoord aTargetY);
+
+  // This interval function is designed to handle the arguments to ::LineLeft()
+  // and LineRight() and interpret them for the supplied aIntervals.
+  static nscoord LineEdge(const nsTArray<nsRect>& aIntervals,
+                          const nscoord aBStart, const nscoord aBEnd,
+                          bool aIsLineLeft);
+
+  // These types, constants, and functions are useful for ShapeInfos that
+  // allocate a distance field. Efficient distance field calculations use
+  // integer values that are 5X the Euclidean distance. MAX_MARGIN_5X is the
+  // largest possible margin that we can calculate (in 5X integer dev pixels),
+  // given these constraints.
+  typedef uint16_t dfType;
+  static const dfType MAX_CHAMFER_VALUE;
+  static const dfType MAX_MARGIN;
+  static const dfType MAX_MARGIN_5X;
+
+  // This function returns a typed, overflow-safe value of aShapeMargin in
+  // 5X integer dev pixels.
+  static dfType CalcUsedShapeMargin5X(nscoord aShapeMargin,
+                                      int32_t aAppUnitsPerDevPixel);
+};
+
+const nsFloatManager::ShapeInfo::dfType
+    nsFloatManager::ShapeInfo::MAX_CHAMFER_VALUE = 11;
+
+const nsFloatManager::ShapeInfo::dfType nsFloatManager::ShapeInfo::MAX_MARGIN =
+    (std::numeric_limits<dfType>::max() - MAX_CHAMFER_VALUE) / 5;
+
+const nsFloatManager::ShapeInfo::dfType
+    nsFloatManager::ShapeInfo::MAX_MARGIN_5X = MAX_MARGIN * 5;
+
+/////////////////////////////////////////////////////////////////////////////
+// EllipseShapeInfo
+//
+// Implements shape-outside: circle() and shape-outside: ellipse().
+//
+class nsFloatManager::EllipseShapeInfo final
+    : public nsFloatManager::ShapeInfo {
+ public:
+  // Construct the float area using math to calculate the shape boundary.
+  // This is the fast path and should be used when shape-margin is negligible,
+  // or when the two values of aRadii are roughly equal. Those two conditions
+  // are defined by ShapeMarginIsNegligible() and RadiiAreRoughlyEqual(). In
+  // those cases, we can conveniently represent the entire float area using
+  // an ellipse.
+  EllipseShapeInfo(const nsPoint& aCenter, const nsSize& aRadii,
+                   nscoord aShapeMargin);
+
+  // Construct the float area using rasterization to calculate the shape
+  // boundary. This constructor accounts for the fact that applying
+  // 'shape-margin' to an ellipse produces a shape that is not mathematically
+  // representable as an ellipse.
+  EllipseShapeInfo(const nsPoint& aCenter, const nsSize& aRadii,
+                   nscoord aShapeMargin, int32_t aAppUnitsPerDevPixel);
+
+  static bool ShapeMarginIsNegligible(nscoord aShapeMargin) {
+    // For now, only return true for a shape-margin of 0. In the future, if
+    // we want to enable use of the fast-path constructor more often, this
+    // limit could be increased;
+    static const nscoord SHAPE_MARGIN_NEGLIGIBLE_MAX(0);
+    return aShapeMargin <= SHAPE_MARGIN_NEGLIGIBLE_MAX;
+  }
+
+  static bool RadiiAreRoughlyEqual(const nsSize& aRadii) {
+    // For now, only return true when we are exactly equal. In the future, if
+    // we want to enable use of the fast-path constructor more often, this
+    // could be generalized to allow radii that are in some close proportion
+    // to each other.
+    return aRadii.width == aRadii.height;
+  }
+  nscoord LineEdge(const nscoord aBStart, const nscoord aBEnd,
+                   bool aLeft) const;
+  nscoord LineLeft(const nscoord aBStart, const nscoord aBEnd) const override;
+  nscoord LineRight(const nscoord aBStart, const nscoord aBEnd) const override;
+  nscoord BStart() const override {
+    return mCenter.y - mRadii.height - mShapeMargin;
+  }
+  nscoord BEnd() const override {
+    return mCenter.y + mRadii.height + mShapeMargin;
+  }
+  bool IsEmpty() const override {
+    // An EllipseShapeInfo is never empty, because an ellipse or circle with
+    // a zero radius acts like a point, and an ellipse with one zero radius
+    // acts like a line.
+    return false;
+  }
+  bool MayNarrowInBlockDirection() const override { return true; }
+
+  void Translate(nscoord aLineLeft, nscoord aBlockStart) override {
+    mCenter.MoveBy(aLineLeft, aBlockStart);
+
+    for (nsRect& interval : mIntervals) {
+      interval.MoveBy(aLineLeft, aBlockStart);
+    }
+  }
+
+ private:
+  // The position of the center of the ellipse. The coordinate space is the
+  // same as FloatInfo::mRect.
+  nsPoint mCenter;
+  // The radii of the ellipse in app units. The width and height represent
+  // the line-axis and block-axis radii of the ellipse.
+  nsSize mRadii;
+  // The shape-margin of the ellipse in app units. If this value is greater
+  // than zero, then we calculate the bounds of the ellipse + margin using
+  // numerical methods and store the values in mIntervals.
+  nscoord mShapeMargin;
+
+  // An interval is slice of the float area defined by this EllipseShapeInfo.
+  // Each interval is a rectangle that is one pixel deep in the block
+  // axis. The values are stored as block edges in the y coordinates,
+  // and inline edges as the x coordinates.
+
+  // The intervals are stored in ascending order on y.
+  nsTArray<nsRect> mIntervals;
+};
+
+nsFloatManager::EllipseShapeInfo::EllipseShapeInfo(const nsPoint& aCenter,
+                                                   const nsSize& aRadii,
+                                                   nscoord aShapeMargin)
+    : mCenter(aCenter),
+      mRadii(aRadii),
+      mShapeMargin(
+          0)  // We intentionally ignore the value of aShapeMargin here.
+{
+  MOZ_ASSERT(
+      RadiiAreRoughlyEqual(aRadii) || ShapeMarginIsNegligible(aShapeMargin),
+      "This constructor should only be called when margin is "
+      "negligible or radii are roughly equal.");
+
+  // We add aShapeMargin into the radii, and we earlier stored a mShapeMargin
+  // of zero.
+  mRadii.width += aShapeMargin;
+  mRadii.height += aShapeMargin;
+}
+
+nsFloatManager::EllipseShapeInfo::EllipseShapeInfo(const nsPoint& aCenter,
+                                                   const nsSize& aRadii,
+                                                   nscoord aShapeMargin,
+                                                   int32_t aAppUnitsPerDevPixel)
+    : mCenter(aCenter), mRadii(aRadii), mShapeMargin(aShapeMargin) {
+  if (RadiiAreRoughlyEqual(aRadii) || ShapeMarginIsNegligible(aShapeMargin)) {
+    // Mimic the behavior of the simple constructor, by adding aShapeMargin
+    // into the radii, and then storing mShapeMargin of zero.
+    mRadii.width += mShapeMargin;
+    mRadii.height += mShapeMargin;
+    mShapeMargin = 0;
+    return;
+  }
+
+  // We have to calculate a distance field from the ellipse edge, then build
+  // intervals based on pixels with less than aShapeMargin distance to an
+  // edge pixel.
+
+  // mCenter and mRadii have already been translated into logical coordinates.
+  // x = inline, y = block. Due to symmetry, we only need to calculate the
+  // distance field for one quadrant of the ellipse. We choose the positive-x,
+  // positive-y quadrant (the lower right quadrant in horizontal-tb writing
+  // mode). We choose this quadrant because it allows us to traverse our
+  // distance field in memory order, which is more cache efficient.
+  // When we apply these intervals in LineLeft() and LineRight(), we
+  // account for block ranges that hit other quadrants, or hit multiple
+  // quadrants.
+
+  // Given this setup, computing the distance field is a one-pass O(n)
+  // operation that runs from block top-to-bottom, inline left-to-right. We
+  // use a chamfer 5-7-11 5x5 matrix to compute minimum distance to an edge
+  // pixel. This integer math computation is reasonably close to the true
+  // Euclidean distance. The distances will be approximately 5x the true
+  // distance, quantized in integer units. The 5x is factored away in the
+  // comparison which builds the intervals.
+  dfType usedMargin5X =
+      CalcUsedShapeMargin5X(aShapeMargin, aAppUnitsPerDevPixel);
+
+  // Calculate the bounds of one quadrant of the ellipse, in integer device
+  // pixels. These bounds are equal to the rectangle defined by the radii,
+  // plus the shape-margin value in both dimensions.
+  const LayoutDeviceIntSize bounds =
+      LayoutDevicePixel::FromAppUnitsRounded(mRadii, aAppUnitsPerDevPixel) +
+      LayoutDeviceIntSize(usedMargin5X / 5, usedMargin5X / 5);
+
+  // Since our distance field is computed with a 5x5 neighborhood, but only
+  // looks in the negative block and negative inline directions, it is
+  // effectively a 3x3 neighborhood. We need to expand our distance field
+  // outwards by a further 2 pixels in both axes (on the minimum block edge
+  // and the minimum inline edge). We call this edge area the expanded region.
+
+  static const uint32_t iExpand = 2;
+  static const uint32_t bExpand = 2;
+
+  // Clamp the size of our distance field sizes to prevent multiplication
+  // overflow.
+  static const uint32_t DF_SIDE_MAX =
+      floor(sqrt((double)(std::numeric_limits<int32_t>::max())));
+  const uint32_t iSize = std::min(bounds.width + iExpand, DF_SIDE_MAX);
+  const uint32_t bSize = std::min(bounds.height + bExpand, DF_SIDE_MAX);
+  auto df = MakeUniqueFallible<dfType[]>(iSize * bSize);
+  if (!df) {
+    // Without a distance field, we can't reason about the float area.
+    return;
+  }
+
+  // Single pass setting distance field, in positive block direction, three
+  // cases:
+  // 1) Expanded region pixel: set to MAX_MARGIN_5X.
+  // 2) Pixel within the ellipse: set to 0.
+  // 3) Other pixel: set to minimum neighborhood distance value, computed
+  //                 with 5-7-11 chamfer.
+
+  for (uint32_t b = 0; b < bSize; ++b) {
+    bool bIsInExpandedRegion(b < bExpand);
+    nscoord bInAppUnits = (b - bExpand) * aAppUnitsPerDevPixel;
+    bool bIsMoreThanEllipseBEnd(bInAppUnits > mRadii.height);
+
+    // Find the i intercept of the ellipse edge for this block row, and
+    // adjust it to compensate for the expansion of the inline dimension.
+    // If we're in the expanded region, or if we're using a b that's more
+    // than the bEnd of the ellipse, the intercept is nscoord_MIN.
+    // We have one other special case to consider: when the ellipse has no
+    // height. In that case we treat the bInAppUnits == 0 case as
+    // intercepting at the width of the ellipse. All other cases solve
+    // the intersection mathematically.
+    const int32_t iIntercept =
+        (bIsInExpandedRegion || bIsMoreThanEllipseBEnd)
+            ? nscoord_MIN
+            : iExpand + NSAppUnitsToIntPixels(
+                            (!!mRadii.height || bInAppUnits)
+                                ? XInterceptAtY(bInAppUnits, mRadii.width,
+                                                mRadii.height)
+                                : mRadii.width,
+                            aAppUnitsPerDevPixel);
+
+    // Set iMax in preparation for this block row.
+    int32_t iMax = iIntercept;
+
+    for (uint32_t i = 0; i < iSize; ++i) {
+      const uint32_t index = i + b * iSize;
+      MOZ_ASSERT(index < (iSize * bSize),
+                 "Our distance field index should be in-bounds.");
+
+      // Handle our three cases, in order.
+      if (i < iExpand || bIsInExpandedRegion) {
+        // Case 1: Expanded reqion pixel.
+        df[index] = MAX_MARGIN_5X;
+      } else if ((int32_t)i <= iIntercept) {
+        // Case 2: Pixel within the ellipse, or just outside the edge of it.
+        // Having a positive height indicates that there's an area we can
+        // be inside of.
+        df[index] = (!!mRadii.height) ? 0 : 5;
+      } else {
+        // Case 3: Other pixel.
+
+        // Backward-looking neighborhood distance from target pixel X
+        // with chamfer 5-7-11 looks like:
+        //
+        // +--+--+--+
+        // |  |11|  |
+        // +--+--+--+
+        // |11| 7| 5|
+        // +--+--+--+
+        // |  | 5| X|
+        // +--+--+--+
+        //
+        // X should be set to the minimum of the values of all of the numbered
+        // neighbors summed with the value in that chamfer cell.
+        MOZ_ASSERT(index - iSize - 2 < (iSize * bSize) &&
+                       index - (iSize * 2) - 1 < (iSize * bSize),
+                   "Our distance field most extreme indices should be "
+                   "in-bounds.");
+
+        // clang-format off
+        df[index] = std::min<dfType>(df[index - 1] + 5,
+                    std::min<dfType>(df[index - iSize] + 5,
+                    std::min<dfType>(df[index - iSize - 1] + 7,
+                    std::min<dfType>(df[index - iSize - 2] + 11,
+                    df[index - (iSize * 2) - 1] + 11))));
+        // clang-format on
+
+        // Check the df value and see if it's less than or equal to the
+        // usedMargin5X value.
+        if (df[index] <= usedMargin5X) {
+          MOZ_ASSERT(iMax < (int32_t)i);
+          iMax = i;
+        } else {
+          // Since we're computing the bottom-right quadrant, there's no way
+          // for a later i value in this row to be within the usedMargin5X
+          // value. Likewise, every row beyond us will encounter this
+          // condition with an i value less than or equal to our i value now.
+          // Since our chamfer only looks upward and leftward, we can stop
+          // calculating for the rest of the row, because the distance field
+          // values there will never be looked at in a later row's chamfer
+          // calculation.
+          break;
+        }
+      }
+    }
+
+    // It's very likely, though not guaranteed that we will find an pixel
+    // within the shape-margin distance for each block row. This may not
+    // always be true due to rounding errors.
+    if (iMax > nscoord_MIN) {
+      // Origin for this interval is at the center of the ellipse, adjusted
+      // in the positive block direction by bInAppUnits.
+      nsPoint origin(aCenter.x, aCenter.y + bInAppUnits);
+      // Size is an inline iMax plus 1 (to account for the whole pixel) dev
+      // pixels, by 1 block dev pixel. We convert this to app units.
+      nsSize size((iMax - iExpand + 1) * aAppUnitsPerDevPixel,
+                  aAppUnitsPerDevPixel);
+      mIntervals.AppendElement(nsRect(origin, size));
+    }
+  }
+}
+
+nscoord nsFloatManager::EllipseShapeInfo::LineEdge(const nscoord aBStart,
+                                                   const nscoord aBEnd,
+                                                   bool aIsLineLeft) const {
+  // If no mShapeMargin, just compute the edge using math.
+  if (mShapeMargin == 0) {
+    nscoord lineDiff = ComputeEllipseLineInterceptDiff(
+        BStart(), BEnd(), mRadii.width, mRadii.height, mRadii.width,
+        mRadii.height, aBStart, aBEnd);
+    return mCenter.x + (aIsLineLeft ? (-mRadii.width + lineDiff)
+                                    : (mRadii.width - lineDiff));
+  }
+
+  // We are checking against our intervals. Make sure we have some.
+  if (mIntervals.IsEmpty()) {
+    NS_WARNING("With mShapeMargin > 0, we can't proceed without intervals.");
+    return aIsLineLeft ? nscoord_MAX : nscoord_MIN;
+  }
+
+  // Map aBStart and aBEnd into our intervals. Our intervals are calculated
+  // for the lower-right quadrant (in terms of horizontal-tb writing mode).
+  // If aBStart and aBEnd span the center of the ellipse, then we know we
+  // are at the maximum displacement from the center.
+  bool bStartIsAboveCenter = (aBStart < mCenter.y);
+  bool bEndIsBelowOrAtCenter = (aBEnd >= mCenter.y);
+  if (bStartIsAboveCenter && bEndIsBelowOrAtCenter) {
+    return mCenter.x + (aIsLineLeft ? (-mRadii.width - mShapeMargin)
+                                    : (mRadii.width + mShapeMargin));
+  }
+
+  // aBStart and aBEnd don't span the center. Since the intervals are
+  // strictly wider approaching the center (the start of the mIntervals
+  // array), we only need to find the interval at the block value closest to
+  // the center. We find the min of aBStart, aBEnd, and their reflections --
+  // whichever two of them are within the lower-right quadrant. When we
+  // reflect from the upper-right quadrant to the lower-right, we have to
+  // subtract 1 from the reflection, to account that block values are always
+  // addressed from the leading block edge.
+
+  // The key example is when we check with aBStart == aBEnd at the top of the
+  // intervals. That block line would be considered contained in the
+  // intervals (though it has no height), but its reflection would not be
+  // within the intervals unless we subtract 1.
+  nscoord bSmallestWithinIntervals = std::min(
+      bStartIsAboveCenter ? aBStart + (mCenter.y - aBStart) * 2 - 1 : aBStart,
+      bEndIsBelowOrAtCenter ? aBEnd : aBEnd + (mCenter.y - aBEnd) * 2 - 1);
+
+  MOZ_ASSERT(bSmallestWithinIntervals >= mCenter.y &&
+                 bSmallestWithinIntervals < BEnd(),
+             "We should have a block value within the float area.");
+
+  size_t index =
+      MinIntervalIndexContainingY(mIntervals, bSmallestWithinIntervals);
+  if (index >= mIntervals.Length()) {
+    // This indicates that our intervals don't cover the block value
+    // bSmallestWithinIntervals. This can happen when rounding error in the
+    // distance field calculation resulted in the last block pixel row not
+    // contributing to the float area. As long as we're within one block pixel
+    // past the last interval, this is an expected outcome.
+#ifdef DEBUG
+    nscoord onePixelPastLastInterval =
+        mIntervals[mIntervals.Length() - 1].YMost() +
+        mIntervals[mIntervals.Length() - 1].Height();
+    NS_WARNING_ASSERTION(bSmallestWithinIntervals < onePixelPastLastInterval,
+                         "We should have found a matching interval for this "
+                         "block value.");
+#endif
+    return aIsLineLeft ? nscoord_MAX : nscoord_MIN;
+  }
+
+  // The interval is storing the line right value. If aIsLineLeft is true,
+  // return the line right value reflected about the center. Since this is
+  // an inline measurement, it's just checking the distance to an edge, and
+  // not a collision with a specific pixel. For that reason, we don't need
+  // to subtract 1 from the reflection, as we did with the block reflection.
+  nscoord iLineRight = mIntervals[index].XMost();
+  return aIsLineLeft ? iLineRight - (iLineRight - mCenter.x) * 2 : iLineRight;
+}
+
+nscoord nsFloatManager::EllipseShapeInfo::LineLeft(const nscoord aBStart,
+                                                   const nscoord aBEnd) const {
+  return LineEdge(aBStart, aBEnd, true);
+}
+
+nscoord nsFloatManager::EllipseShapeInfo::LineRight(const nscoord aBStart,
+                                                    const nscoord aBEnd) const {
+  return LineEdge(aBStart, aBEnd, false);
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// RoundedBoxShapeInfo
+//
+// Implements shape-outside: <shape-box> and shape-outside: inset().
+//
+class nsFloatManager::RoundedBoxShapeInfo final
+    : public nsFloatManager::ShapeInfo {
+ public:
+  RoundedBoxShapeInfo(const nsRect& aRect, UniquePtr<nscoord[]> aRadii)
+      : mRect(aRect), mRadii(std::move(aRadii)), mShapeMargin(0) {}
+
+  RoundedBoxShapeInfo(const nsRect& aRect, UniquePtr<nscoord[]> aRadii,
+                      nscoord aShapeMargin, int32_t aAppUnitsPerDevPixel);
+
+  nscoord LineLeft(const nscoord aBStart, const nscoord aBEnd) const override;
+  nscoord LineRight(const nscoord aBStart, const nscoord aBEnd) const override;
+  nscoord BStart() const override { return mRect.y; }
+  nscoord BEnd() const override { return mRect.YMost(); }
+  bool IsEmpty() const override {
+    // A RoundedBoxShapeInfo is never empty, because if it is collapsed to
+    // zero area, it acts like a point. If it is collapsed further, to become
+    // inside-out, it acts like a rect in the same shape as the inside-out
+    // rect.
+    return false;
+  }
+  bool MayNarrowInBlockDirection() const override {
+    // Only possible to narrow if there are non-null mRadii.
+    return !!mRadii;
+  }
+
+  void Translate(nscoord aLineLeft, nscoord aBlockStart) override {
+    mRect.MoveBy(aLineLeft, aBlockStart);
+
+    if (mShapeMargin > 0) {
+      MOZ_ASSERT(mLogicalTopLeftCorner && mLogicalTopRightCorner &&
+                     mLogicalBottomLeftCorner && mLogicalBottomRightCorner,
+                 "If we have positive shape-margin, we should have corners.");
+      mLogicalTopLeftCorner->Translate(aLineLeft, aBlockStart);
+      mLogicalTopRightCorner->Translate(aLineLeft, aBlockStart);
+      mLogicalBottomLeftCorner->Translate(aLineLeft, aBlockStart);
+      mLogicalBottomRightCorner->Translate(aLineLeft, aBlockStart);
+    }
+  }
+
+  static bool EachCornerHasBalancedRadii(const nscoord* aRadii) {
+    return (aRadii[eCornerTopLeftX] == aRadii[eCornerTopLeftY] &&
+            aRadii[eCornerTopRightX] == aRadii[eCornerTopRightY] &&
+            aRadii[eCornerBottomLeftX] == aRadii[eCornerBottomLeftY] &&
+            aRadii[eCornerBottomRightX] == aRadii[eCornerBottomRightY]);
+  }
+
+ private:
+  // The rect of the rounded box shape in the float manager's coordinate
+  // space.
+  nsRect mRect;
+  // The half corner radii of the reference box. It's an nscoord[8] array
+  // in the float manager's coordinate space. If there are no radii, it's
+  // nullptr.
+  const UniquePtr<nscoord[]> mRadii;
+
+  // A shape-margin value extends the boundaries of the float area. When our
+  // first constructor is used, it is for the creation of rounded boxes that
+  // can ignore shape-margin -- either because it was specified as zero or
+  // because the box shape and radii can be inflated to account for it. When
+  // our second constructor is used, we store the shape-margin value here.
+  const nscoord mShapeMargin;
+
+  // If our second constructor is called (which implies mShapeMargin > 0),
+  // we will construct EllipseShapeInfo objects for each corner. We use the
+  // float logical naming here, where LogicalTopLeftCorner means the BStart
+  // LineLeft corner, and similarly for the other corners.
+  UniquePtr<EllipseShapeInfo> mLogicalTopLeftCorner;
+  UniquePtr<EllipseShapeInfo> mLogicalTopRightCorner;
+  UniquePtr<EllipseShapeInfo> mLogicalBottomLeftCorner;
+  UniquePtr<EllipseShapeInfo> mLogicalBottomRightCorner;
+};
+
+nsFloatManager::RoundedBoxShapeInfo::RoundedBoxShapeInfo(
+    const nsRect& aRect, UniquePtr<nscoord[]> aRadii, nscoord aShapeMargin,
+    int32_t aAppUnitsPerDevPixel)
+    : mRect(aRect), mRadii(std::move(aRadii)), mShapeMargin(aShapeMargin) {
+  MOZ_ASSERT(mShapeMargin > 0 && !EachCornerHasBalancedRadii(mRadii.get()),
+             "Slow constructor should only be used for for shape-margin > 0 "
+             "and radii with elliptical corners.");
+
+  // Before we inflate mRect by mShapeMargin, construct each of our corners.
+  // If we do it in this order, it's a bit simpler to calculate the center
+  // of each of the corners.
+  mLogicalTopLeftCorner = MakeUnique<EllipseShapeInfo>(
+      nsPoint(mRect.X() + mRadii[eCornerTopLeftX],
+              mRect.Y() + mRadii[eCornerTopLeftY]),
+      nsSize(mRadii[eCornerTopLeftX], mRadii[eCornerTopLeftY]), mShapeMargin,
+      aAppUnitsPerDevPixel);
+
+  mLogicalTopRightCorner = MakeUnique<EllipseShapeInfo>(
+      nsPoint(mRect.XMost() - mRadii[eCornerTopRightX],
+              mRect.Y() + mRadii[eCornerTopRightY]),
+      nsSize(mRadii[eCornerTopRightX], mRadii[eCornerTopRightY]), mShapeMargin,
+      aAppUnitsPerDevPixel);
+
+  mLogicalBottomLeftCorner = MakeUnique<EllipseShapeInfo>(
+      nsPoint(mRect.X() + mRadii[eCornerBottomLeftX],
+              mRect.YMost() - mRadii[eCornerBottomLeftY]),
+      nsSize(mRadii[eCornerBottomLeftX], mRadii[eCornerBottomLeftY]),
+      mShapeMargin, aAppUnitsPerDevPixel);
+
+  mLogicalBottomRightCorner = MakeUnique<EllipseShapeInfo>(
+      nsPoint(mRect.XMost() - mRadii[eCornerBottomRightX],
+              mRect.YMost() - mRadii[eCornerBottomRightY]),
+      nsSize(mRadii[eCornerBottomRightX], mRadii[eCornerBottomRightY]),
+      mShapeMargin, aAppUnitsPerDevPixel);
+
+  // Now we inflate our mRect by mShapeMargin.
+  mRect.Inflate(mShapeMargin);
+}
+
+nscoord nsFloatManager::RoundedBoxShapeInfo::LineLeft(
+    const nscoord aBStart, const nscoord aBEnd) const {
+  if (mShapeMargin == 0) {
+    if (!mRadii) {
+      return mRect.x;
+    }
+
+    nscoord lineLeftDiff = ComputeEllipseLineInterceptDiff(
+        mRect.y, mRect.YMost(), mRadii[eCornerTopLeftX],
+        mRadii[eCornerTopLeftY], mRadii[eCornerBottomLeftX],
+        mRadii[eCornerBottomLeftY], aBStart, aBEnd);
+    return mRect.x + lineLeftDiff;
+  }
+
+  MOZ_ASSERT(mLogicalTopLeftCorner && mLogicalBottomLeftCorner,
+             "If we have positive shape-margin, we should have corners.");
+
+  // Determine if aBEnd is within our top corner.
+  if (aBEnd < mLogicalTopLeftCorner->BEnd()) {
+    return mLogicalTopLeftCorner->LineLeft(aBStart, aBEnd);
+  }
+
+  // Determine if aBStart is within our bottom corner.
+  if (aBStart >= mLogicalBottomLeftCorner->BStart()) {
+    return mLogicalBottomLeftCorner->LineLeft(aBStart, aBEnd);
+  }
+
+  // Either aBStart or aBEnd or both are within the flat part of our left
+  // edge. Because we've already inflated our mRect to encompass our
+  // mShapeMargin, we can just return the edge.
+  return mRect.X();
+}
+
+nscoord nsFloatManager::RoundedBoxShapeInfo::LineRight(
+    const nscoord aBStart, const nscoord aBEnd) const {
+  if (mShapeMargin == 0) {
+    if (!mRadii) {
+      return mRect.XMost();
+    }
+
+    nscoord lineRightDiff = ComputeEllipseLineInterceptDiff(
+        mRect.y, mRect.YMost(), mRadii[eCornerTopRightX],
+        mRadii[eCornerTopRightY], mRadii[eCornerBottomRightX],
+        mRadii[eCornerBottomRightY], aBStart, aBEnd);
+    return mRect.XMost() - lineRightDiff;
+  }
+
+  MOZ_ASSERT(mLogicalTopRightCorner && mLogicalBottomRightCorner,
+             "If we have positive shape-margin, we should have corners.");
+
+  // Determine if aBEnd is within our top corner.
+  if (aBEnd < mLogicalTopRightCorner->BEnd()) {
+    return mLogicalTopRightCorner->LineRight(aBStart, aBEnd);
+  }
+
+  // Determine if aBStart is within our bottom corner.
+  if (aBStart >= mLogicalBottomRightCorner->BStart()) {
+    return mLogicalBottomRightCorner->LineRight(aBStart, aBEnd);
+  }
+
+  // Either aBStart or aBEnd or both are within the flat part of our right
+  // edge. Because we've already inflated our mRect to encompass our
+  // mShapeMargin, we can just return the edge.
+  return mRect.XMost();
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// PolygonShapeInfo
+//
+// Implements shape-outside: polygon().
+//
+class nsFloatManager::PolygonShapeInfo final
+    : public nsFloatManager::ShapeInfo {
+ public:
+  explicit PolygonShapeInfo(nsTArray<nsPoint>&& aVertices);
+  PolygonShapeInfo(nsTArray<nsPoint>&& aVertices, nscoord aShapeMargin,
+                   int32_t aAppUnitsPerDevPixel, const nsRect& aMarginRect);
+
+  nscoord LineLeft(const nscoord aBStart, const nscoord aBEnd) const override;
+  nscoord LineRight(const nscoord aBStart, const nscoord aBEnd) const override;
+  nscoord BStart() const override { return mBStart; }
+  nscoord BEnd() const override { return mBEnd; }
+  bool IsEmpty() const override {
+    // A PolygonShapeInfo is never empty, because the parser prevents us from
+    // creating a shape with no vertices. If we only have 1 vertex, the
+    // shape acts like a point. With 2 non-coincident vertices, the shape
+    // acts like a line.
+    return false;
+  }
+  bool MayNarrowInBlockDirection() const override { return true; }
+
+  void Translate(nscoord aLineLeft, nscoord aBlockStart) override;
+
+ private:
+  // Helper method for determining the mBStart and mBEnd based on the
+  // vertices' y extent.
+  void ComputeExtent();
+
+  // Helper method for implementing LineLeft() and LineRight().
+  nscoord ComputeLineIntercept(
+      const nscoord aBStart, const nscoord aBEnd,
+      nscoord (*aCompareOp)(std::initializer_list<nscoord>),
+      const nscoord aLineInterceptInitialValue) const;
+
+  // Given a horizontal line y, and two points p1 and p2 forming a line
+  // segment L. Solve x for the intersection of y and L. This method
+  // assumes y and L do intersect, and L is *not* horizontal.
+  static nscoord XInterceptAtY(const nscoord aY, const nsPoint& aP1,
+                               const nsPoint& aP2);
+
+  // The vertices of the polygon in the float manager's coordinate space.
+  nsTArray<nsPoint> mVertices;
+
+  // An interval is slice of the float area defined by this PolygonShapeInfo.
+  // These are only generated and used in float area calculations for
+  // shape-margin > 0. Each interval is a rectangle that is one device pixel
+  // deep in the block axis. The values are stored as block edges in the y
+  // coordinates, and inline edges as the x coordinates.
+
+  // The intervals are stored in ascending order on y.
+  nsTArray<nsRect> mIntervals;
+
+  // Computed block start and block end value of the polygon shape. These
+  // initial values are set to correct values in ComputeExtent(), which is
+  // called from all constructors. Afterwards, mBStart is guaranteed to be
+  // less than or equal to mBEnd.
+  nscoord mBStart = nscoord_MAX;
+  nscoord mBEnd = nscoord_MIN;
+};
+
+nsFloatManager::PolygonShapeInfo::PolygonShapeInfo(
+    nsTArray<nsPoint>&& aVertices)
+    : mVertices(std::move(aVertices)) {
+  ComputeExtent();
+}
+
+nsFloatManager::PolygonShapeInfo::PolygonShapeInfo(
+    nsTArray<nsPoint>&& aVertices, nscoord aShapeMargin,
+    int32_t aAppUnitsPerDevPixel, const nsRect& aMarginRect)
+    : mVertices(std::move(aVertices)) {
+  MOZ_ASSERT(aShapeMargin > 0,
+             "This constructor should only be used for a "
+             "polygon with a positive shape-margin.");
+
+  ComputeExtent();
+
+  // With a positive aShapeMargin, we have to calculate a distance
+  // field from the opaque pixels, then build intervals based on
+  // them being within aShapeMargin distance to an opaque pixel.
+
+  // Roughly: for each pixel in the margin box, we need to determine the
+  // distance to the nearest opaque image-pixel.  If that distance is less
+  // than aShapeMargin, we consider this margin-box pixel as being part of
+  // the float area.
+
+  // Computing the distance field is a two-pass O(n) operation.
+  // We use a chamfer 5-7-11 5x5 matrix to compute minimum distance
+  // to an opaque pixel. This integer math computation is reasonably
+  // close to the true Euclidean distance. The distances will be
+  // approximately 5x the true distance, quantized in integer units.
+  // The 5x is factored away in the comparison used in the final
+  // pass which builds the intervals.
+  dfType usedMargin5X =
+      CalcUsedShapeMargin5X(aShapeMargin, aAppUnitsPerDevPixel);
+
+  // Allocate our distance field.  The distance field has to cover
+  // the entire aMarginRect, since aShapeMargin could bleed into it.
+  // Conveniently, our vertices have been converted into this same space,
+  // so if we cover the aMarginRect, we cover all the vertices.
+  const LayoutDeviceIntSize marginRectDevPixels =
+      LayoutDevicePixel::FromAppUnitsRounded(aMarginRect.Size(),
+                                             aAppUnitsPerDevPixel);
+
+  // Since our distance field is computed with a 5x5 neighborhood,
+  // we need to expand our distance field by a further 4 pixels in
+  // both axes, 2 on the leading edge and 2 on the trailing edge.
+  // We call this edge area the "expanded region".
+  static const uint32_t kiExpansionPerSide = 2;
+  static const uint32_t kbExpansionPerSide = 2;
+
+  // Clamp the size of our distance field sizes to prevent multiplication
+  // overflow.
+  static const uint32_t DF_SIDE_MAX =
+      floor(sqrt((double)(std::numeric_limits<int32_t>::max())));
+
+  // Clamp the margin plus 2X the expansion values between expansion + 1 and
+  // DF_SIDE_MAX. This ensures that the distance field allocation doesn't
+  // overflow during multiplication, and the reverse iteration doesn't
+  // underflow.
+  const uint32_t iSize =
+      std::max(std::min(marginRectDevPixels.width + (kiExpansionPerSide * 2),
+                        DF_SIDE_MAX),
+               kiExpansionPerSide + 1);
+  const uint32_t bSize =
+      std::max(std::min(marginRectDevPixels.height + (kbExpansionPerSide * 2),
+                        DF_SIDE_MAX),
+               kbExpansionPerSide + 1);
+
+  // Since the margin-box size is CSS controlled, and large values will
+  // generate large iSize and bSize values, we do a fallible allocation for
+  // the distance field. If allocation fails, we early exit and layout will
+  // be wrong, but we'll avoid aborting from OOM.
+  auto df = MakeUniqueFallible<dfType[]>(iSize * bSize);
+  if (!df) {
+    // Without a distance field, we can't reason about the float area.
+    return;
+  }
+
+  // First pass setting distance field, starting at top-left, three cases:
+  // 1) Expanded region pixel: set to MAX_MARGIN_5X.
+  // 2) Pixel within the polygon: set to 0.
+  // 3) Other pixel: set to minimum backward-looking neighborhood
+  //                 distance value, computed with 5-7-11 chamfer.
+
+  for (uint32_t b = 0; b < bSize; ++b) {
+    // Find the left and right i intercepts of the polygon edge for this
+    // block row, and adjust them to compensate for the expansion of the
+    // inline dimension. If we're in the expanded region, or if we're using
+    // a b that's less than the bStart of the polygon, the intercepts are
+    // the nscoord min and max limits.
+    nscoord bInAppUnits = (b - kbExpansionPerSide) * aAppUnitsPerDevPixel;
+    bool bIsInExpandedRegion(b < kbExpansionPerSide ||
+                             b >= bSize - kbExpansionPerSide);
+
+    // We now figure out the i values that correspond to the left edge and
+    // the right edge of the polygon at one-dev-pixel-thick strip of b. We
+    // have a ComputeLineIntercept function that takes and returns app unit
+    // coordinates in the space of aMarginRect. So to pass in b values, we
+    // first have to add the aMarginRect.y value. And for the values that we
+    // get out, we have to subtract away the aMarginRect.x value before
+    // converting the app units to dev pixels.
+    nscoord bInAppUnitsMarginRect = bInAppUnits + aMarginRect.y;
+    bool bIsLessThanPolygonBStart(bInAppUnitsMarginRect < mBStart);
+    bool bIsMoreThanPolygonBEnd(bInAppUnitsMarginRect > mBEnd);
+
+    const int32_t iLeftEdge =
+        (bIsInExpandedRegion || bIsLessThanPolygonBStart ||
+         bIsMoreThanPolygonBEnd)
+            ? nscoord_MAX
+            : kiExpansionPerSide +
+                  NSAppUnitsToIntPixels(
+                      ComputeLineIntercept(
+                          bInAppUnitsMarginRect,
+                          bInAppUnitsMarginRect + aAppUnitsPerDevPixel,
+                          std::min<nscoord>, nscoord_MAX) -
+                          aMarginRect.x,
+                      aAppUnitsPerDevPixel);
+
+    const int32_t iRightEdge =
+        (bIsInExpandedRegion || bIsLessThanPolygonBStart ||
+         bIsMoreThanPolygonBEnd)
+            ? nscoord_MIN
+            : kiExpansionPerSide +
+                  NSAppUnitsToIntPixels(
+                      ComputeLineIntercept(
+                          bInAppUnitsMarginRect,
+                          bInAppUnitsMarginRect + aAppUnitsPerDevPixel,
+                          std::max<nscoord>, nscoord_MIN) -
+                          aMarginRect.x,
+                      aAppUnitsPerDevPixel);
+
+    for (uint32_t i = 0; i < iSize; ++i) {
+      const uint32_t index = i + b * iSize;
+      MOZ_ASSERT(index < (iSize * bSize),
+                 "Our distance field index should be in-bounds.");
+
+      // Handle our three cases, in order.
+      if (i < kiExpansionPerSide || i >= iSize - kiExpansionPerSide ||
+          bIsInExpandedRegion) {
+        // Case 1: Expanded pixel.
+        df[index] = MAX_MARGIN_5X;
+      } else if ((int32_t)i >= iLeftEdge && (int32_t)i <= iRightEdge) {
+        // Case 2: Polygon pixel, either inside or just adjacent to the right
+        // edge. We need this special distinction to detect a space between
+        // edges that is less than one dev pixel.
+        df[index] = (int32_t)i < iRightEdge ? 0 : 5;
+      } else {
+        // Case 3: Other pixel.
+
+        // Backward-looking neighborhood distance from target pixel X
+        // with chamfer 5-7-11 looks like:
+        //
+        // +--+--+--+--+--+
+        // |  |11|  |11|  |
+        // +--+--+--+--+--+
+        // |11| 7| 5| 7|11|
+        // +--+--+--+--+--+
+        // |  | 5| X|  |  |
+        // +--+--+--+--+--+
+        //
+        // X should be set to the minimum of MAX_MARGIN_5X and the
+        // values of all of the numbered neighbors summed with the
+        // value in that chamfer cell.
+        MOZ_ASSERT(index - (iSize * 2) - 1 < (iSize * bSize) &&
+                       index - iSize - 2 < (iSize * bSize),
+                   "Our distance field most extreme indices should be "
+                   "in-bounds.");
+
+        // clang-format off
+        df[index] = std::min<dfType>(MAX_MARGIN_5X,
+                    std::min<dfType>(df[index - (iSize * 2) - 1] + 11,
+                    std::min<dfType>(df[index - (iSize * 2) + 1] + 11,
+                    std::min<dfType>(df[index - iSize - 2] + 11,
+                    std::min<dfType>(df[index - iSize - 1] + 7,
+                    std::min<dfType>(df[index - iSize] + 5,
+                    std::min<dfType>(df[index - iSize + 1] + 7,
+                    std::min<dfType>(df[index - iSize + 2] + 11,
+                                     df[index - 1] + 5))))))));
+        // clang-format on
+      }
+    }
+  }
+
+  // Okay, time for the second pass. This pass is in reverse order from
+  // the first pass. All of our opaque pixels have been set to 0, and all
+  // of our expanded region pixels have been set to MAX_MARGIN_5X. Other
+  // pixels have been set to some value between those two (inclusive) but
+  // this hasn't yet taken into account the neighbors that were processed
+  // after them in the first pass. This time we reverse iterate so we can
+  // apply the forward-looking chamfer.
+
+  // This time, we constrain our outer and inner loop to ignore the
+  // expanded region pixels. For each pixel we iterate, we set the df value
+  // to the minimum forward-looking neighborhood distance value, computed
+  // with a 5-7-11 chamfer. We also check each df value against the
+  // usedMargin5X threshold, and use that to set the iMin and iMax values
+  // for the interval we'll create for that block axis value (b).
+
+  // At the end of each row, if any of the other pixels had a value less
+  // than usedMargin5X, we create an interval.
+  for (uint32_t b = bSize - kbExpansionPerSide - 1; b >= kbExpansionPerSide;
+       --b) {
+    // iMin tracks the first df pixel and iMax the last df pixel whose
+    // df[] value is less than usedMargin5X. Set iMin and iMax in
+    // preparation for this row or column.
+    int32_t iMin = iSize;
+    int32_t iMax = -1;
+
+    for (uint32_t i = iSize - kiExpansionPerSide - 1; i >= kiExpansionPerSide;
+         --i) {
+      const uint32_t index = i + b * iSize;
+      MOZ_ASSERT(index < (iSize * bSize),
+                 "Our distance field index should be in-bounds.");
+
+      // Only apply the chamfer calculation if the df value is not
+      // already 0, since the chamfer can only reduce the value.
+      if (df[index]) {
+        // Forward-looking neighborhood distance from target pixel X
+        // with chamfer 5-7-11 looks like:
+        //
+        // +--+--+--+--+--+
+        // |  |  | X| 5|  |
+        // +--+--+--+--+--+
+        // |11| 7| 5| 7|11|
+        // +--+--+--+--+--+
+        // |  |11|  |11|  |
+        // +--+--+--+--+--+
+        //
+        // X should be set to the minimum of its current value and
+        // the values of all of the numbered neighbors summed with
+        // the value in that chamfer cell.
+        MOZ_ASSERT(index + (iSize * 2) + 1 < (iSize * bSize) &&
+                       index + iSize + 2 < (iSize * bSize),
+                   "Our distance field most extreme indices should be "
+                   "in-bounds.");
+
+        // clang-format off
+        df[index] = std::min<dfType>(df[index],
+                    std::min<dfType>(df[index + (iSize * 2) + 1] + 11,
+                    std::min<dfType>(df[index + (iSize * 2) - 1] + 11,
+                    std::min<dfType>(df[index + iSize + 2] + 11,
+                    std::min<dfType>(df[index + iSize + 1] + 7,
+                    std::min<dfType>(df[index + iSize] + 5,
+                    std::min<dfType>(df[index + iSize - 1] + 7,
+                    std::min<dfType>(df[index + iSize - 2] + 11,
+                                     df[index + 1] + 5))))))));
+        // clang-format on
+      }
+
+      // Finally, we can check the df value and see if it's less than
+      // or equal to the usedMargin5X value.
+      if (df[index] <= usedMargin5X) {
+        if (iMax == -1) {
+          iMax = i;
+        }
+        MOZ_ASSERT(iMin > (int32_t)i);
+        iMin = i;
+      }
+    }
+
+    if (iMax != -1) {
+      // Our interval values, iMin, iMax, and b are all calculated from
+      // the expanded region, which is based on the margin rect. To create
+      // our interval, we have to subtract kiExpansionPerSide from iMin and
+      // iMax, and subtract kbExpansionPerSide from b to account for the
+      // expanded region edges.  This produces coords that are relative to
+      // our margin-rect.
+
+      // Origin for this interval is at the aMarginRect origin, adjusted in
+      // the block direction by b in app units, and in the inline direction
+      // by iMin in app units.
+      nsPoint origin(
+          aMarginRect.x + (iMin - kiExpansionPerSide) * aAppUnitsPerDevPixel,
+          aMarginRect.y + (b - kbExpansionPerSide) * aAppUnitsPerDevPixel);
+
+      // Size is the difference in iMax and iMin, plus 1 (to account for the
+      // whole pixel) dev pixels, by 1 block dev pixel. We don't bother
+      // subtracting kiExpansionPerSide from iMin and iMax in this case
+      // because we only care about the distance between them. We convert
+      // everything to app units.
+      nsSize size((iMax - iMin + 1) * aAppUnitsPerDevPixel,
+                  aAppUnitsPerDevPixel);
+
+      mIntervals.AppendElement(nsRect(origin, size));
+    }
+  }
+
+  // Reverse the intervals keep the array sorted on the block direction.
+  mIntervals.Reverse();
+
+  // Adjust our extents by aShapeMargin. This may cause overflow of some
+  // kind if aShapeMargin is large, so we do some clamping to maintain the
+  // invariant mBStart <= mBEnd.
+  mBStart = std::min(mBStart, mBStart - aShapeMargin);
+  mBEnd = std::max(mBEnd, mBEnd + aShapeMargin);
+}
+
+nscoord nsFloatManager::PolygonShapeInfo::LineLeft(const nscoord aBStart,
+                                                   const nscoord aBEnd) const {
+  // Use intervals if we have them.
+  if (!mIntervals.IsEmpty()) {
+    return LineEdge(mIntervals, aBStart, aBEnd, true);
+  }
+
+  // We want the line-left-most inline-axis coordinate where the
+  // (block-axis) aBStart/aBEnd band crosses a line segment of the polygon.
+  // To get that, we start as line-right as possible (at nscoord_MAX). Then
+  // we iterate each line segment to compute its intersection point with the
+  // band (if any) and using std::min() successively to get the smallest
+  // inline-coordinates among those intersection points.
+  //
+  // Note: std::min<nscoord> means the function std::min() with template
+  // parameter nscoord, not the minimum value of nscoord.
+  return ComputeLineIntercept(aBStart, aBEnd, std::min<nscoord>, nscoord_MAX);
+}
+
+nscoord nsFloatManager::PolygonShapeInfo::LineRight(const nscoord aBStart,
+                                                    const nscoord aBEnd) const {
+  // Use intervals if we have them.
+  if (!mIntervals.IsEmpty()) {
+    return LineEdge(mIntervals, aBStart, aBEnd, false);
+  }
+
+  // Similar to LineLeft(). Though here, we want the line-right-most
+  // inline-axis coordinate, so we instead start at nscoord_MIN and use
+  // std::max() to get the biggest inline-coordinate among those
+  // intersection points.
+  return ComputeLineIntercept(aBStart, aBEnd, std::max<nscoord>, nscoord_MIN);
+}
+
+void nsFloatManager::PolygonShapeInfo::ComputeExtent() {
+  // mBStart and mBEnd are the lower and the upper bounds of all the
+  // vertex.y, respectively. The vertex.y is actually on the block-axis of
+  // the float manager's writing mode.
+  for (const nsPoint& vertex : mVertices) {
+    mBStart = std::min(mBStart, vertex.y);
+    mBEnd = std::max(mBEnd, vertex.y);
+  }
+
+  MOZ_ASSERT(mBStart <= mBEnd,
+             "Start of float area should be less than "
+             "or equal to the end.");
+}
+
+nscoord nsFloatManager::PolygonShapeInfo::ComputeLineIntercept(
+    const nscoord aBStart, const nscoord aBEnd,
+    nscoord (*aCompareOp)(std::initializer_list<nscoord>),
+    const nscoord aLineInterceptInitialValue) const {
+  MOZ_ASSERT(aBStart <= aBEnd,
+             "The band's block start is greater than its block end?");
+
+  const size_t len = mVertices.Length();
+  nscoord lineIntercept = aLineInterceptInitialValue;
+
+  // We have some special treatment of horizontal lines between vertices.
+  // Generally, we can ignore the impact of the horizontal lines since their
+  // endpoints will be included in the lines preceeding or following them.
+  // However, it's possible the polygon is entirely a horizontal line,
+  // possibly built from more than one horizontal segment. In such a case,
+  // we need to have the horizontal line(s) contribute to the line intercepts.
+  // We do this by accepting horizontal lines until we find a non-horizontal
+  // line, after which all further horizontal lines are ignored.
+  bool canIgnoreHorizontalLines = false;
+
+  // Iterate each line segment {p0, p1}, {p1, p2}, ..., {pn, p0}.
+  for (size_t i = 0; i < len; ++i) {
+    const nsPoint* smallYVertex = &mVertices[i];
+    const nsPoint* bigYVertex = &mVertices[(i + 1) % len];
+
+    // Swap the two points to satisfy the requirement for calling
+    // XInterceptAtY.
+    if (smallYVertex->y > bigYVertex->y) {
+      std::swap(smallYVertex, bigYVertex);
+    }
+
+    // Generally, we need to ignore line segments that either don't intersect
+    // the band, or merely touch it. However, if the polygon has no block extent
+    // (it is a point, or a horizontal line), and the band touches the line
+    // segment, we let that line segment through.
+    if ((aBStart >= bigYVertex->y || aBEnd <= smallYVertex->y) &&
+        !(mBStart == mBEnd && aBStart == bigYVertex->y)) {
+      // Skip computing the intercept if the band doesn't intersect the
+      // line segment.
+      continue;
+    }
+
+    nscoord bStartLineIntercept;
+    nscoord bEndLineIntercept;
+
+    if (smallYVertex->y == bigYVertex->y) {
+      // The line is horizontal; see if we can ignore it.
+      if (canIgnoreHorizontalLines) {
+        continue;
+      }
+
+      // For a horizontal line that we can't ignore, we treat the two x value
+      // ends as the bStartLineIntercept and bEndLineIntercept. It doesn't
+      // matter which is applied to which, because they'll both be applied
+      // to aCompareOp.
+      bStartLineIntercept = smallYVertex->x;
+      bEndLineIntercept = bigYVertex->x;
+    } else {
+      // This is not a horizontal line. We can now ignore all future
+      // horizontal lines.
+      canIgnoreHorizontalLines = true;
+
+      bStartLineIntercept =
+          aBStart <= smallYVertex->y
+              ? smallYVertex->x
+              : XInterceptAtY(aBStart, *smallYVertex, *bigYVertex);
+      bEndLineIntercept =
+          aBEnd >= bigYVertex->y
+              ? bigYVertex->x
+              : XInterceptAtY(aBEnd, *smallYVertex, *bigYVertex);
+    }
+
+    // If either new intercept is more extreme than lineIntercept (per
+    // aCompareOp), then update lineIntercept to that value.
+    lineIntercept =
+        aCompareOp({lineIntercept, bStartLineIntercept, bEndLineIntercept});
+  }
+
+  return lineIntercept;
+}
+
+void nsFloatManager::PolygonShapeInfo::Translate(nscoord aLineLeft,
+                                                 nscoord aBlockStart) {
+  for (nsPoint& vertex : mVertices) {
+    vertex.MoveBy(aLineLeft, aBlockStart);
+  }
+  for (nsRect& interval : mIntervals) {
+    interval.MoveBy(aLineLeft, aBlockStart);
+  }
+  mBStart += aBlockStart;
+  mBEnd += aBlockStart;
+}
+
+/* static */
+nscoord nsFloatManager::PolygonShapeInfo::XInterceptAtY(const nscoord aY,
+                                                        const nsPoint& aP1,
+                                                        const nsPoint& aP2) {
+  // Solve for x in the linear equation: x = x1 + (y-y1) * (x2-x1) / (y2-y1),
+  // where aP1 = (x1, y1) and aP2 = (x2, y2).
+
+  MOZ_ASSERT(aP1.y <= aY && aY <= aP2.y,
+             "This function won't work if the horizontal line at aY and "
+             "the line segment (aP1, aP2) do not intersect!");
+
+  MOZ_ASSERT(aP1.y != aP2.y,
+             "A horizontal line segment results in dividing by zero error!");
+
+  return aP1.x + (aY - aP1.y) * (aP2.x - aP1.x) / (aP2.y - aP1.y);
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// ImageShapeInfo
+//
+// Implements shape-outside: <image>
+//
+class nsFloatManager::ImageShapeInfo final : public nsFloatManager::ShapeInfo {
+ public:
+  ImageShapeInfo(uint8_t* aAlphaPixels, int32_t aStride,
+                 const LayoutDeviceIntSize& aImageSize,
+                 int32_t aAppUnitsPerDevPixel, float aShapeImageThreshold,
+                 nscoord aShapeMargin, const nsRect& aContentRect,
+                 const nsRect& aMarginRect, WritingMode aWM,
+                 const nsSize& aContainerSize);
+
+  nscoord LineLeft(const nscoord aBStart, const nscoord aBEnd) const override;
+  nscoord LineRight(const nscoord aBStart, const nscoord aBEnd) const override;
+  nscoord BStart() const override { return mBStart; }
+  nscoord BEnd() const override { return mBEnd; }
+  bool IsEmpty() const override { return mIntervals.IsEmpty(); }
+  bool MayNarrowInBlockDirection() const override { return true; }
+
+  void Translate(nscoord aLineLeft, nscoord aBlockStart) override;
+
+ private:
+  // An interval is slice of the float area defined by this ImageShapeInfo.
+  // Each interval is a rectangle that is one pixel deep in the block
+  // axis. The values are stored as block edges in the y coordinates,
+  // and inline edges as the x coordinates.
+
+  // The intervals are stored in ascending order on y.
+  nsTArray<nsRect> mIntervals;
+
+  nscoord mBStart = nscoord_MAX;
+  nscoord mBEnd = nscoord_MIN;
+
+  // CreateInterval transforms the supplied aIMin and aIMax and aB
+  // values into an interval that respects the writing mode. An
+  // aOffsetFromContainer can be provided if the aIMin, aIMax, aB
+  // values were generated relative to something other than the container
+  // rect (such as the content rect or margin rect).
+  void CreateInterval(int32_t aIMin, int32_t aIMax, int32_t aB,
+                      int32_t aAppUnitsPerDevPixel,
+                      const nsPoint& aOffsetFromContainer, WritingMode aWM,
+                      const nsSize& aContainerSize);
+};
+
+nsFloatManager::ImageShapeInfo::ImageShapeInfo(
+    uint8_t* aAlphaPixels, int32_t aStride,
+    const LayoutDeviceIntSize& aImageSize, int32_t aAppUnitsPerDevPixel,
+    float aShapeImageThreshold, nscoord aShapeMargin,
+    const nsRect& aContentRect, const nsRect& aMarginRect, WritingMode aWM,
+    const nsSize& aContainerSize) {
+  MOZ_ASSERT(aShapeImageThreshold >= 0.0 && aShapeImageThreshold <= 1.0,
+             "The computed value of shape-image-threshold is wrong!");
+
+  const uint8_t threshold = NSToIntFloor(aShapeImageThreshold * 255);
+
+  MOZ_ASSERT(aImageSize.width >= 0 && aImageSize.height >= 0,
+             "Image size must be non-negative for our math to work.");
+  const uint32_t w = aImageSize.width;
+  const uint32_t h = aImageSize.height;
+
+  if (aShapeMargin <= 0) {
+    // Without a positive aShapeMargin, all we have to do is a
+    // direct threshold comparison of the alpha pixels.
+    // https://drafts.csswg.org/css-shapes-1/#valdef-shape-image-threshold-number
+
+    // Scan the pixels in a double loop. For horizontal writing modes, we do
+    // this row by row, from top to bottom. For vertical writing modes, we do
+    // column by column, from left to right. We define the two loops
+    // generically, then figure out the rows and cols within the inner loop.
+    const uint32_t bSize = aWM.IsVertical() ? w : h;
+    const uint32_t iSize = aWM.IsVertical() ? h : w;
+    for (uint32_t b = 0; b < bSize; ++b) {
+      // iMin and max store the start and end of the float area for the row
+      // or column represented by this iteration of the outer loop.
+      int32_t iMin = -1;
+      int32_t iMax = -1;
+
+      for (uint32_t i = 0; i < iSize; ++i) {
+        const uint32_t col = aWM.IsVertical() ? b : i;
+        const uint32_t row = aWM.IsVertical() ? i : b;
+        const uint32_t index = col + row * aStride;
+
+        // Determine if the alpha pixel at this row and column has a value
+        // greater than the threshold. If it does, update our iMin and iMax
+        // values to track the edges of the float area for this row or column.
+        // https://drafts.csswg.org/css-shapes-1/#valdef-shape-image-threshold-number
+        const uint8_t alpha = aAlphaPixels[index];
+        if (alpha > threshold) {
+          if (iMin == -1) {
+            iMin = i;
+          }
+          MOZ_ASSERT(iMax < (int32_t)i);
+          iMax = i;
+        }
+      }
+
+      // At the end of a row or column; did we find something?
+      if (iMin != -1) {
+        // We need to supply an offset of the content rect top left, since
+        // our col and row have been calculated from the content rect,
+        // instead of the margin rect (against which floats are applied).
+        CreateInterval(iMin, iMax, b, aAppUnitsPerDevPixel,
+                       aContentRect.TopLeft(), aWM, aContainerSize);
+      }
+    }
+
+    if (aWM.IsVerticalRL()) {
+      // vertical-rl or sideways-rl.
+      // Because we scan the columns from left to right, we need to reverse
+      // the array so that it's sorted (in ascending order) on the block
+      // direction.
+      mIntervals.Reverse();
+    }
+  } else {
+    // With a positive aShapeMargin, we have to calculate a distance
+    // field from the opaque pixels, then build intervals based on
+    // them being within aShapeMargin distance to an opaque pixel.
+
+    // Roughly: for each pixel in the margin box, we need to determine the
+    // distance to the nearest opaque image-pixel.  If that distance is less
+    // than aShapeMargin, we consider this margin-box pixel as being part of
+    // the float area.
+
+    // Computing the distance field is a two-pass O(n) operation.
+    // We use a chamfer 5-7-11 5x5 matrix to compute minimum distance
+    // to an opaque pixel. This integer math computation is reasonably
+    // close to the true Euclidean distance. The distances will be
+    // approximately 5x the true distance, quantized in integer units.
+    // The 5x is factored away in the comparison used in the final
+    // pass which builds the intervals.
+    dfType usedMargin5X =
+        CalcUsedShapeMargin5X(aShapeMargin, aAppUnitsPerDevPixel);
+
+    // Allocate our distance field.  The distance field has to cover
+    // the entire aMarginRect, since aShapeMargin could bleed into it,
+    // beyond the content rect covered by aAlphaPixels. To make this work,
+    // we calculate a dfOffset value which is the top left of the content
+    // rect relative to the margin rect.
+    nsPoint offsetPoint = aContentRect.TopLeft() - aMarginRect.TopLeft();
+    LayoutDeviceIntPoint dfOffset = LayoutDevicePixel::FromAppUnitsRounded(
+        offsetPoint, aAppUnitsPerDevPixel);
+
+    // Since our distance field is computed with a 5x5 neighborhood,
+    // we need to expand our distance field by a further 4 pixels in
+    // both axes, 2 on the leading edge and 2 on the trailing edge.
+    // We call this edge area the "expanded region".
+
+    // Our expansion amounts need to be the same for our math to work.
+    static uint32_t kExpansionPerSide = 2;
+    // Since dfOffset will be used in comparisons against expanded region
+    // pixel values, it's convenient to add expansion amounts to dfOffset in
+    // both axes, to simplify comparison math later.
+    dfOffset.x += kExpansionPerSide;
+    dfOffset.y += kExpansionPerSide;
+
+    // In all these calculations, we purposely ignore aStride, because
+    // we don't have to replicate the packing that we received in
+    // aAlphaPixels. When we need to convert from df coordinates to
+    // alpha coordinates, we do that with math based on row and col.
+    const LayoutDeviceIntSize marginRectDevPixels =
+        LayoutDevicePixel::FromAppUnitsRounded(aMarginRect.Size(),
+                                               aAppUnitsPerDevPixel);
+
+    // Clamp the size of our distance field sizes to prevent multiplication
+    // overflow.
+    static const uint32_t DF_SIDE_MAX =
+        floor(sqrt((double)(std::numeric_limits<int32_t>::max())));
+
+    // Clamp the margin plus 2X the expansion values between expansion + 1
+    // and DF_SIDE_MAX. This ensures that the distance field allocation
+    // doesn't overflow during multiplication, and the reverse iteration
+    // doesn't underflow.
+    const uint32_t wEx =
+        std::max(std::min(marginRectDevPixels.width + (kExpansionPerSide * 2),
+                          DF_SIDE_MAX),
+                 kExpansionPerSide + 1);
+    const uint32_t hEx =
+        std::max(std::min(marginRectDevPixels.height + (kExpansionPerSide * 2),
+                          DF_SIDE_MAX),
+                 kExpansionPerSide + 1);
+
+    // Since the margin-box size is CSS controlled, and large values will
+    // generate large wEx and hEx values, we do a falliable allocation for
+    // the distance field. If allocation fails, we early exit and layout will
+    // be wrong, but we'll avoid aborting from OOM.
+    auto df = MakeUniqueFallible<dfType[]>(wEx * hEx);
+    if (!df) {
+      // Without a distance field, we can't reason about the float area.
+      return;
+    }
+
+    const uint32_t bSize = aWM.IsVertical() ? wEx : hEx;
+    const uint32_t iSize = aWM.IsVertical() ? hEx : wEx;
+
+    // First pass setting distance field, starting at top-left, three cases:
+    // 1) Expanded region pixel: set to MAX_MARGIN_5X.
+    // 2) Image pixel with alpha greater than threshold: set to 0.
+    // 3) Other pixel: set to minimum backward-looking neighborhood
+    //                 distance value, computed with 5-7-11 chamfer.
+
+    // Scan the pixels in a double loop. For horizontal writing modes, we do
+    // this row by row, from top to bottom. For vertical writing modes, we do
+    // column by column, from left to right. We define the two loops
+    // generically, then figure out the rows and cols within the inner loop.
+    for (uint32_t b = 0; b < bSize; ++b) {
+      for (uint32_t i = 0; i < iSize; ++i) {
+        const uint32_t col = aWM.IsVertical() ? b : i;
+        const uint32_t row = aWM.IsVertical() ? i : b;
+        const uint32_t index = col + row * wEx;
+        MOZ_ASSERT(index < (wEx * hEx),
+                   "Our distance field index should be in-bounds.");
+
+        // Handle our three cases, in order.
+        if (col < kExpansionPerSide || col >= wEx - kExpansionPerSide ||
+            row < kExpansionPerSide || row >= hEx - kExpansionPerSide) {
+          // Case 1: Expanded pixel.
+          df[index] = MAX_MARGIN_5X;
+        } else if ((int32_t)col >= dfOffset.x &&
+                   (int32_t)col < (dfOffset.x + aImageSize.width) &&
+                   (int32_t)row >= dfOffset.y &&
+                   (int32_t)row < (dfOffset.y + aImageSize.height) &&
+                   aAlphaPixels[col - dfOffset.x.value +
+                                (row - dfOffset.y.value) * aStride] >
+                       threshold) {
+          // Case 2: Image pixel that is opaque.
+          DebugOnly<uint32_t> alphaIndex =
+              col - dfOffset.x.value + (row - dfOffset.y.value) * aStride;
+          MOZ_ASSERT(alphaIndex < (aStride * h),
+                     "Our aAlphaPixels index should be in-bounds.");
+
+          df[index] = 0;
+        } else {
+          // Case 3: Other pixel.
+          if (aWM.IsVertical()) {
+            // Column-by-column, starting at the left, each column
+            // top-to-bottom.
+            // Backward-looking neighborhood distance from target pixel X
+            // with chamfer 5-7-11 looks like:
+            //
+            // +--+--+--+
+            // |  |11|  |   |    +
+            // +--+--+--+   |   /|
+            // |11| 7| 5|   |  / |
+            // +--+--+--+   | /  V
+            // |  | 5| X|   |/
+            // +--+--+--+   +
+            // |11| 7|  |
+            // +--+--+--+
+            // |  |11|  |
+            // +--+--+--+
+            //
+            // X should be set to the minimum of MAX_MARGIN_5X and the
+            // values of all of the numbered neighbors summed with the
+            // value in that chamfer cell.
+            MOZ_ASSERT(index - wEx - 2 < (iSize * bSize) &&
+                           index + wEx - 2 < (iSize * bSize) &&
+                           index - (wEx * 2) - 1 < (iSize * bSize),
+                       "Our distance field most extreme indices should be "
+                       "in-bounds.");
+
+            // clang-format off
+            df[index] = std::min<dfType>(MAX_MARGIN_5X,
+                        std::min<dfType>(df[index - wEx - 2] + 11,
+                        std::min<dfType>(df[index + wEx - 2] + 11,
+                        std::min<dfType>(df[index - (wEx * 2) - 1] + 11,
+                        std::min<dfType>(df[index - wEx - 1] + 7,
+                        std::min<dfType>(df[index - 1] + 5,
+                        std::min<dfType>(df[index + wEx - 1] + 7,
+                        std::min<dfType>(df[index + (wEx * 2) - 1] + 11,
+                                         df[index - wEx] + 5))))))));
+            // clang-format on
+          } else {
+            // Row-by-row, starting at the top, each row left-to-right.
+            // Backward-looking neighborhood distance from target pixel X
+            // with chamfer 5-7-11 looks like:
+            //
+            // +--+--+--+--+--+
+            // |  |11|  |11|  |   ----+
+            // +--+--+--+--+--+      /
+            // |11| 7| 5| 7|11|     /
+            // +--+--+--+--+--+    /
+            // |  | 5| X|  |  |   +-->
+            // +--+--+--+--+--+
+            //
+            // X should be set to the minimum of MAX_MARGIN_5X and the
+            // values of all of the numbered neighbors summed with the
+            // value in that chamfer cell.
+            MOZ_ASSERT(index - (wEx * 2) - 1 < (iSize * bSize) &&
+                           index - wEx - 2 < (iSize * bSize),
+                       "Our distance field most extreme indices should be "
+                       "in-bounds.");
+
+            // clang-format off
+            df[index] = std::min<dfType>(MAX_MARGIN_5X,
+                        std::min<dfType>(df[index - (wEx * 2) - 1] + 11,
+                        std::min<dfType>(df[index - (wEx * 2) + 1] + 11,
+                        std::min<dfType>(df[index - wEx - 2] + 11,
+                        std::min<dfType>(df[index - wEx - 1] + 7,
+                        std::min<dfType>(df[index - wEx] + 5,
+                        std::min<dfType>(df[index - wEx + 1] + 7,
+                        std::min<dfType>(df[index - wEx + 2] + 11,
+                                         df[index - 1] + 5))))))));
+            // clang-format on
+          }
+        }
+      }
+    }
+
+    // Okay, time for the second pass. This pass is in reverse order from
+    // the first pass. All of our opaque pixels have been set to 0, and all
+    // of our expanded region pixels have been set to MAX_MARGIN_5X. Other
+    // pixels have been set to some value between those two (inclusive) but
+    // this hasn't yet taken into account the neighbors that were processed
+    // after them in the first pass. This time we reverse iterate so we can
+    // apply the forward-looking chamfer.
+
+    // This time, we constrain our outer and inner loop to ignore the
+    // expanded region pixels. For each pixel we iterate, we set the df value
+    // to the minimum forward-looking neighborhood distance value, computed
+    // with a 5-7-11 chamfer. We also check each df value against the
+    // usedMargin5X threshold, and use that to set the iMin and iMax values
+    // for the interval we'll create for that block axis value (b).
+
+    // At the end of each row (or column in vertical writing modes),
+    // if any of the other pixels had a value less than usedMargin5X,
+    // we create an interval. Note: "bSize - kExpansionPerSide - 1" is the
+    // index of the final row of pixels before the trailing expanded region.
+    for (uint32_t b = bSize - kExpansionPerSide - 1; b >= kExpansionPerSide;
+         --b) {
+      // iMin tracks the first df pixel and iMax the last df pixel whose
+      // df[] value is less than usedMargin5X. Set iMin and iMax in
+      // preparation for this row or column.
+      int32_t iMin = iSize;
+      int32_t iMax = -1;
+
+      // Note: "iSize - kExpansionPerSide - 1" is the index of the final row
+      // of pixels before the trailing expanded region.
+      for (uint32_t i = iSize - kExpansionPerSide - 1; i >= kExpansionPerSide;
+           --i) {
+        const uint32_t col = aWM.IsVertical() ? b : i;
+        const uint32_t row = aWM.IsVertical() ? i : b;
+        const uint32_t index = col + row * wEx;
+        MOZ_ASSERT(index < (wEx * hEx),
+                   "Our distance field index should be in-bounds.");
+
+        // Only apply the chamfer calculation if the df value is not
+        // already 0, since the chamfer can only reduce the value.
+        if (df[index]) {
+          if (aWM.IsVertical()) {
+            // Column-by-column, starting at the right, each column
+            // bottom-to-top.
+            // Forward-looking neighborhood distance from target pixel X
+            // with chamfer 5-7-11 looks like:
+            //
+            // +--+--+--+
+            // |  |11|  |        +
+            // +--+--+--+       /|
+            // |  | 7|11|   A  / |
+            // +--+--+--+   | /  |
+            // | X| 5|  |   |/   |
+            // +--+--+--+   +    |
+            // | 5| 7|11|
+            // +--+--+--+
+            // |  |11|  |
+            // +--+--+--+
+            //
+            // X should be set to the minimum of its current value and
+            // the values of all of the numbered neighbors summed with
+            // the value in that chamfer cell.
+            MOZ_ASSERT(index + wEx + 2 < (wEx * hEx) &&
+                           index + (wEx * 2) + 1 < (wEx * hEx) &&
+                           index - (wEx * 2) + 1 < (wEx * hEx),
+                       "Our distance field most extreme indices should be "
+                       "in-bounds.");
+
+            // clang-format off
+            df[index] = std::min<dfType>(df[index],
+                        std::min<dfType>(df[index + wEx + 2] + 11,
+                        std::min<dfType>(df[index - wEx + 2] + 11,
+                        std::min<dfType>(df[index + (wEx * 2) + 1] + 11,
+                        std::min<dfType>(df[index + wEx + 1] + 7,
+                        std::min<dfType>(df[index + 1] + 5,
+                        std::min<dfType>(df[index - wEx + 1] + 7,
+                        std::min<dfType>(df[index - (wEx * 2) + 1] + 11,
+                                         df[index + wEx] + 5))))))));
+            // clang-format on
+          } else {
+            // Row-by-row, starting at the bottom, each row right-to-left.
+            // Forward-looking neighborhood distance from target pixel X
+            // with chamfer 5-7-11 looks like:
+            //
+            // +--+--+--+--+--+
+            // |  |  | X| 5|  |    <--+
+            // +--+--+--+--+--+      /
+            // |11| 7| 5| 7|11|     /
+            // +--+--+--+--+--+    /
+            // |  |11|  |11|  |   +----
+            // +--+--+--+--+--+
+            //
+            // X should be set to the minimum of its current value and
+            // the values of all of the numbered neighbors summed with
+            // the value in that chamfer cell.
+            MOZ_ASSERT(index + (wEx * 2) + 1 < (wEx * hEx) &&
+                           index + wEx + 2 < (wEx * hEx),
+                       "Our distance field most extreme indices should be "
+                       "in-bounds.");
+
+            // clang-format off
+            df[index] = std::min<dfType>(df[index],
+                        std::min<dfType>(df[index + (wEx * 2) + 1] + 11,
+                        std::min<dfType>(df[index + (wEx * 2) - 1] + 11,
+                        std::min<dfType>(df[index + wEx + 2] + 11,
+                        std::min<dfType>(df[index + wEx + 1] + 7,
+                        std::min<dfType>(df[index + wEx] + 5,
+                        std::min<dfType>(df[index + wEx - 1] + 7,
+                        std::min<dfType>(df[index + wEx - 2] + 11,
+                                         df[index + 1] + 5))))))));
+            // clang-format on
+          }
+        }
+
+        // Finally, we can check the df value and see if it's less than
+        // or equal to the usedMargin5X value.
+        if (df[index] <= usedMargin5X) {
+          if (iMax == -1) {
+            iMax = i;
+          }
+          MOZ_ASSERT(iMin > (int32_t)i);
+          iMin = i;
+        }
+      }
+
+      if (iMax != -1) {
+        // Our interval values, iMin, iMax, and b are all calculated from
+        // the expanded region, which is based on the margin rect. To create
+        // our interval, we have to subtract kExpansionPerSide from (iMin,
+        // iMax, and b) to account for the expanded region edges. This
+        // produces coords that are relative to our margin-rect, so we pass
+        // in aMarginRect.TopLeft() to make CreateInterval convert to our
+        // container's coordinate space.
+        CreateInterval(iMin - kExpansionPerSide, iMax - kExpansionPerSide,
+                       b - kExpansionPerSide, aAppUnitsPerDevPixel,
+                       aMarginRect.TopLeft(), aWM, aContainerSize);
+      }
+    }
+
+    if (!aWM.IsVerticalRL()) {
+      // Anything other than vertical-rl or sideways-rl.
+      // Because we assembled our intervals on the bottom-up pass,
+      // they are reversed for most writing modes. Reverse them to
+      // keep the array sorted on the block direction.
+      mIntervals.Reverse();
+    }
+  }
+
+  if (!mIntervals.IsEmpty()) {
+    mBStart = mIntervals[0].Y();
+    mBEnd = mIntervals.LastElement().YMost();
+  }
+}
+
+void nsFloatManager::ImageShapeInfo::CreateInterval(
+    int32_t aIMin, int32_t aIMax, int32_t aB, int32_t aAppUnitsPerDevPixel,
+    const nsPoint& aOffsetFromContainer, WritingMode aWM,
+    const nsSize& aContainerSize) {
+  // Store an interval as an nsRect with our inline axis values stored in x
+  // and our block axis values stored in y. The position is dependent on
+  // the writing mode, but the size is the same for all writing modes.
+
+  // Size is the difference in inline axis edges stored as x, and one
+  // block axis pixel stored as y. For the inline axis, we add 1 to aIMax
+  // because we want to capture the far edge of the last pixel.
+  nsSize size(((aIMax + 1) - aIMin) * aAppUnitsPerDevPixel,
+              aAppUnitsPerDevPixel);
+
+  // Since we started our scanning of the image pixels from the top left,
+  // the interval position starts from the origin of the content rect,
+  // converted to logical coordinates.
+  nsPoint origin =
+      ConvertToFloatLogical(aOffsetFromContainer, aWM, aContainerSize);
+
+  // Depending on the writing mode, we now move the origin.
+  if (aWM.IsVerticalRL()) {
+    // vertical-rl or sideways-rl.
+    // These writing modes proceed from the top right, and each interval
+    // moves in a positive inline direction and negative block direction.
+    // That means that the intervals will be reversed after all have been
+    // constructed. We add 1 to aB to capture the end of the block axis pixel.
+    origin.MoveBy(aIMin * aAppUnitsPerDevPixel,
+                  (aB + 1) * -aAppUnitsPerDevPixel);
+  } else if (aWM.IsSidewaysLR()) {
+    // This writing mode proceeds from the bottom left, and each interval
+    // moves in a negative inline direction and a positive block direction.
+    // We add 1 to aIMax to capture the end of the inline axis pixel.
+    origin.MoveBy((aIMax + 1) * -aAppUnitsPerDevPixel,
+                  aB * aAppUnitsPerDevPixel);
+  } else {
+    // horizontal-tb or vertical-lr.
+    // These writing modes proceed from the top left and each interval
+    // moves in a positive step in both inline and block directions.
+    origin.MoveBy(aIMin * aAppUnitsPerDevPixel, aB * aAppUnitsPerDevPixel);
+  }
+
+  mIntervals.AppendElement(nsRect(origin, size));
+}
+
+nscoord nsFloatManager::ImageShapeInfo::LineLeft(const nscoord aBStart,
+                                                 const nscoord aBEnd) const {
+  return LineEdge(mIntervals, aBStart, aBEnd, true);
+}
+
+nscoord nsFloatManager::ImageShapeInfo::LineRight(const nscoord aBStart,
+                                                  const nscoord aBEnd) const {
+  return LineEdge(mIntervals, aBStart, aBEnd, false);
+}
+
+void nsFloatManager::ImageShapeInfo::Translate(nscoord aLineLeft,
+                                               nscoord aBlockStart) {
+  for (nsRect& interval : mIntervals) {
+    interval.MoveBy(aLineLeft, aBlockStart);
+  }
+
+  mBStart += aBlockStart;
+  mBEnd += aBlockStart;
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// FloatInfo
+
+nsFloatManager::FloatInfo::FloatInfo(nsIFrame* aFrame, nscoord aLineLeft,
+                                     nscoord aBlockStart,
+                                     const LogicalRect& aMarginRect,
+                                     WritingMode aWM,
+                                     const nsSize& aContainerSize)
+    : mFrame(aFrame),
+      mLeftBEnd(nscoord_MIN),
+      mRightBEnd(nscoord_MIN),
+      mRect(ShapeInfo::ConvertToFloatLogical(aMarginRect, aWM, aContainerSize) +
+            nsPoint(aLineLeft, aBlockStart)) {
+  MOZ_COUNT_CTOR(nsFloatManager::FloatInfo);
+  using ShapeOutsideType = StyleShapeOutside::Tag;
+
+  if (IsEmpty()) {
+    // Per spec, a float area defined by a shape is clipped to the float’s
+    // margin box. Therefore, no need to create a shape info if the float's
+    // margin box is empty, since a float area can only be smaller than the
+    // margin box.
+
+    // https://drafts.csswg.org/css-shapes/#relation-to-box-model-and-float-behavior
+    return;
+  }
+
+  const nsStyleDisplay* styleDisplay = mFrame->StyleDisplay();
+  const auto& shapeOutside = styleDisplay->mShapeOutside;
+
+  nscoord shapeMargin = shapeOutside.IsNone()
+                            ? 0
+                            : nsLayoutUtils::ResolveToLength<true>(
+                                  styleDisplay->mShapeMargin,
+                                  LogicalSize(aWM, aContainerSize).ISize(aWM));
+
+  switch (shapeOutside.tag) {
+    case ShapeOutsideType::None:
+      // No need to create shape info.
+      return;
+
+    case ShapeOutsideType::Image: {
+      float shapeImageThreshold = styleDisplay->mShapeImageThreshold;
+      mShapeInfo = ShapeInfo::CreateImageShape(
+          shapeOutside.AsImage(), shapeImageThreshold, shapeMargin, mFrame,
+          aMarginRect, aWM, aContainerSize);
+      if (!mShapeInfo) {
+        // Image is not ready, or fails to load, etc.
+        return;
+      }
+
+      break;
+    }
+
+    case ShapeOutsideType::Box: {
+      // Initialize <shape-box>'s reference rect.
+      LogicalRect shapeBoxRect = ShapeInfo::ComputeShapeBoxRect(
+          shapeOutside.AsBox(), mFrame, aMarginRect, aWM);
+      mShapeInfo = ShapeInfo::CreateShapeBox(mFrame, shapeMargin, shapeBoxRect,
+                                             aWM, aContainerSize);
+      break;
+    }
+
+    case ShapeOutsideType::Shape: {
+      const auto& shape = *shapeOutside.AsShape()._0;
+      // Initialize <shape-box>'s reference rect.
+      LogicalRect shapeBoxRect = ShapeInfo::ComputeShapeBoxRect(
+          shapeOutside.AsShape()._1, mFrame, aMarginRect, aWM);
+      mShapeInfo =
+          ShapeInfo::CreateBasicShape(shape, shapeMargin, mFrame, shapeBoxRect,
+                                      aMarginRect, aWM, aContainerSize);
+      break;
+    }
+  }
+
+  MOZ_ASSERT(mShapeInfo,
+             "All shape-outside values except none should have mShapeInfo!");
+
+  // Translate the shape to the same origin as nsFloatManager.
+  mShapeInfo->Translate(aLineLeft, aBlockStart);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsFloatManager::FloatInfo::FloatInfo(FloatInfo&& aOther)
+    : mFrame(std::move(aOther.mFrame)),
+      mLeftBEnd(std::move(aOther.mLeftBEnd)),
+      mRightBEnd(std::move(aOther.mRightBEnd)),
+      mRect(std::move(aOther.mRect)),
+      mShapeInfo(std::move(aOther.mShapeInfo)) {
+  MOZ_COUNT_CTOR(nsFloatManager::FloatInfo);
+}
+
+nsFloatManager::FloatInfo::~FloatInfo() {
+  MOZ_COUNT_DTOR(nsFloatManager::FloatInfo);
+}
+#endif
+
+nscoord nsFloatManager::FloatInfo::LineLeft(ShapeType aShapeType,
+                                            const nscoord aBStart,
+                                            const nscoord aBEnd) const {
+  if (aShapeType == ShapeType::Margin) {
+    return LineLeft();
+  }
+
+  MOZ_ASSERT(aShapeType == ShapeType::ShapeOutside);
+  if (!mShapeInfo) {
+    return LineLeft();
+  }
+  // Clip the flow area to the margin-box because
+  // https://drafts.csswg.org/css-shapes-1/#relation-to-box-model-and-float-behavior
+  // says "When a shape is used to define a float area, the shape is clipped
+  // to the float’s margin box."
+  return std::max(LineLeft(), mShapeInfo->LineLeft(aBStart, aBEnd));
+}
+
+nscoord nsFloatManager::FloatInfo::LineRight(ShapeType aShapeType,
+                                             const nscoord aBStart,
+                                             const nscoord aBEnd) const {
+  if (aShapeType == ShapeType::Margin) {
+    return LineRight();
+  }
+
+  MOZ_ASSERT(aShapeType == ShapeType::ShapeOutside);
+  if (!mShapeInfo) {
+    return LineRight();
+  }
+  // Clip the flow area to the margin-box. See LineLeft().
+  return std::min(LineRight(), mShapeInfo->LineRight(aBStart, aBEnd));
+}
+
+nscoord nsFloatManager::FloatInfo::BStart(ShapeType aShapeType) const {
+  if (aShapeType == ShapeType::Margin) {
+    return BStart();
+  }
+
+  MOZ_ASSERT(aShapeType == ShapeType::ShapeOutside);
+  if (!mShapeInfo) {
+    return BStart();
+  }
+  // Clip the flow area to the margin-box. See LineLeft().
+  return std::max(BStart(), mShapeInfo->BStart());
+}
+
+nscoord nsFloatManager::FloatInfo::BEnd(ShapeType aShapeType) const {
+  if (aShapeType == ShapeType::Margin) {
+    return BEnd();
+  }
+
+  MOZ_ASSERT(aShapeType == ShapeType::ShapeOutside);
+  if (!mShapeInfo) {
+    return BEnd();
+  }
+  // Clip the flow area to the margin-box. See LineLeft().
+  return std::min(BEnd(), mShapeInfo->BEnd());
+}
+
+bool nsFloatManager::FloatInfo::IsEmpty(ShapeType aShapeType) const {
+  if (aShapeType == ShapeType::Margin) {
+    return IsEmpty();
+  }
+
+  MOZ_ASSERT(aShapeType == ShapeType::ShapeOutside);
+  if (!mShapeInfo) {
+    return IsEmpty();
+  }
+  return mShapeInfo->IsEmpty();
+}
+
+bool nsFloatManager::FloatInfo::MayNarrowInBlockDirection(
+    ShapeType aShapeType) const {
+  // This function mirrors the cases of the three argument versions of
+  // LineLeft() and LineRight(). This function returns true if and only if
+  // either of those functions could possibly return "narrower" values with
+  // increasing aBStart values. "Narrower" means closer to the far end of
+  // the float shape.
+  if (aShapeType == ShapeType::Margin) {
+    return false;
+  }
+
+  MOZ_ASSERT(aShapeType == ShapeType::ShapeOutside);
+  if (!mShapeInfo) {
+    return false;
+  }
+
+  return mShapeInfo->MayNarrowInBlockDirection();
+}
+
+/////////////////////////////////////////////////////////////////////////////
+// ShapeInfo
+
+/* static */
+LogicalRect nsFloatManager::ShapeInfo::ComputeShapeBoxRect(
+    StyleShapeBox aBox, nsIFrame* const aFrame, const LogicalRect& aMarginRect,
+    WritingMode aWM) {
+  LogicalRect rect = aMarginRect;
+
+  switch (aBox) {
+    case StyleShapeBox::ContentBox:
+      rect.Deflate(aWM, aFrame->GetLogicalUsedPadding(aWM));
+      [[fallthrough]];
+    case StyleShapeBox::PaddingBox:
+      rect.Deflate(aWM, aFrame->GetLogicalUsedBorder(aWM));
+      [[fallthrough]];
+    case StyleShapeBox::BorderBox:
+      rect.Deflate(aWM, aFrame->GetLogicalUsedMargin(aWM));
+      break;
+    case StyleShapeBox::MarginBox:
+      // Do nothing. rect is already a margin rect.
+      break;
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unknown shape box");
+      break;
+  }
+
+  return rect;
+}
+
+/* static */ UniquePtr<nsFloatManager::ShapeInfo>
+nsFloatManager::ShapeInfo::CreateShapeBox(nsIFrame* const aFrame,
+                                          nscoord aShapeMargin,
+                                          const LogicalRect& aShapeBoxRect,
+                                          WritingMode aWM,
+                                          const nsSize& aContainerSize) {
+  nsRect logicalShapeBoxRect =
+      ConvertToFloatLogical(aShapeBoxRect, aWM, aContainerSize);
+
+  // Inflate logicalShapeBoxRect by aShapeMargin.
+  logicalShapeBoxRect.Inflate(aShapeMargin);
+
+  nscoord physicalRadii[8];
+  bool hasRadii = aFrame->GetShapeBoxBorderRadii(physicalRadii);
+  if (!hasRadii) {
+    return MakeUnique<RoundedBoxShapeInfo>(logicalShapeBoxRect,
+                                           UniquePtr<nscoord[]>());
+  }
+
+  // Add aShapeMargin to each of the radii.
+  for (nscoord& r : physicalRadii) {
+    r += aShapeMargin;
+  }
+
+  return MakeUnique<RoundedBoxShapeInfo>(
+      logicalShapeBoxRect, ConvertToFloatLogical(physicalRadii, aWM));
+}
+
+/* static */ UniquePtr<nsFloatManager::ShapeInfo>
+nsFloatManager::ShapeInfo::CreateBasicShape(const StyleBasicShape& aBasicShape,
+                                            nscoord aShapeMargin,
+                                            nsIFrame* const aFrame,
+                                            const LogicalRect& aShapeBoxRect,
+                                            const LogicalRect& aMarginRect,
+                                            WritingMode aWM,
+                                            const nsSize& aContainerSize) {
+  switch (aBasicShape.tag) {
+    case StyleBasicShape::Tag::Polygon:
+      return CreatePolygon(aBasicShape, aShapeMargin, aFrame, aShapeBoxRect,
+                           aMarginRect, aWM, aContainerSize);
+    case StyleBasicShape::Tag::Circle:
+    case StyleBasicShape::Tag::Ellipse:
+      return CreateCircleOrEllipse(aBasicShape, aShapeMargin, aFrame,
+                                   aShapeBoxRect, aWM, aContainerSize);
+    case StyleBasicShape::Tag::Inset:
+      return CreateInset(aBasicShape, aShapeMargin, aFrame, aShapeBoxRect, aWM,
+                         aContainerSize);
+  }
+  return nullptr;
+}
+
+/* static */ UniquePtr<nsFloatManager::ShapeInfo>
+nsFloatManager::ShapeInfo::CreateInset(const StyleBasicShape& aBasicShape,
+                                       nscoord aShapeMargin, nsIFrame* aFrame,
+                                       const LogicalRect& aShapeBoxRect,
+                                       WritingMode aWM,
+                                       const nsSize& aContainerSize) {
+  // Use physical coordinates to compute inset() because the top, right,
+  // bottom and left offsets are physical.
+  // https://drafts.csswg.org/css-shapes-1/#funcdef-inset
+  nsRect physicalShapeBoxRect =
+      aShapeBoxRect.GetPhysicalRect(aWM, aContainerSize);
+  const nsRect insetRect =
+      ShapeUtils::ComputeInsetRect(aBasicShape, physicalShapeBoxRect);
+
+  nsRect logicalInsetRect = ConvertToFloatLogical(
+      LogicalRect(aWM, insetRect, aContainerSize), aWM, aContainerSize);
+  nscoord physicalRadii[8];
+  bool hasRadii = ShapeUtils::ComputeInsetRadii(
+      aBasicShape, physicalShapeBoxRect, insetRect, physicalRadii);
+
+  // With a zero shape-margin, we will be able to use the fast constructor.
+  if (aShapeMargin == 0) {
+    if (!hasRadii) {
+      return MakeUnique<RoundedBoxShapeInfo>(logicalInsetRect,
+                                             UniquePtr<nscoord[]>());
+    }
+    return MakeUnique<RoundedBoxShapeInfo>(
+        logicalInsetRect, ConvertToFloatLogical(physicalRadii, aWM));
+  }
+
+  // With a positive shape-margin, we might still be able to use the fast
+  // constructor. With no radii, we can build a rounded box by inflating
+  // logicalInsetRect, and supplying aShapeMargin as the radius for all
+  // corners.
+  if (!hasRadii) {
+    logicalInsetRect.Inflate(aShapeMargin);
+    auto logicalRadii = MakeUnique<nscoord[]>(8);
+    for (int32_t i = 0; i < 8; ++i) {
+      logicalRadii[i] = aShapeMargin;
+    }
+    return MakeUnique<RoundedBoxShapeInfo>(logicalInsetRect,
+                                           std::move(logicalRadii));
+  }
+
+  // If we have radii, and they have balanced/equal corners, we can inflate
+  // both logicalInsetRect and all the radii and use the fast constructor.
+  if (RoundedBoxShapeInfo::EachCornerHasBalancedRadii(physicalRadii)) {
+    logicalInsetRect.Inflate(aShapeMargin);
+    for (nscoord& r : physicalRadii) {
+      r += aShapeMargin;
+    }
+    return MakeUnique<RoundedBoxShapeInfo>(
+        logicalInsetRect, ConvertToFloatLogical(physicalRadii, aWM));
+  }
+
+  // With positive shape-margin and elliptical radii, we have to use the
+  // slow constructor.
+  nsDeviceContext* dc = aFrame->PresContext()->DeviceContext();
+  int32_t appUnitsPerDevPixel = dc->AppUnitsPerDevPixel();
+  return MakeUnique<RoundedBoxShapeInfo>(
+      logicalInsetRect, ConvertToFloatLogical(physicalRadii, aWM), aShapeMargin,
+      appUnitsPerDevPixel);
+}
+
+/* static */ UniquePtr<nsFloatManager::ShapeInfo>
+nsFloatManager::ShapeInfo::CreateCircleOrEllipse(
+    const StyleBasicShape& aBasicShape, nscoord aShapeMargin,
+    nsIFrame* const aFrame, const LogicalRect& aShapeBoxRect, WritingMode aWM,
+    const nsSize& aContainerSize) {
+  // Use physical coordinates to compute the center of circle() or ellipse()
+  // since the <position> keywords such as 'left', 'top', etc. are physical.
+  // https://drafts.csswg.org/css-shapes-1/#funcdef-ellipse
+  nsRect physicalShapeBoxRect =
+      aShapeBoxRect.GetPhysicalRect(aWM, aContainerSize);
+  nsPoint physicalCenter = ShapeUtils::ComputeCircleOrEllipseCenter(
+      aBasicShape, physicalShapeBoxRect);
+  nsPoint logicalCenter =
+      ConvertToFloatLogical(physicalCenter, aWM, aContainerSize);
+
+  // Compute the circle or ellipse radii.
+  nsSize radii;
+  if (aBasicShape.IsCircle()) {
+    nscoord radius = ShapeUtils::ComputeCircleRadius(
+        aBasicShape, physicalCenter, physicalShapeBoxRect);
+    // Circles can use the three argument, math constructor for
+    // EllipseShapeInfo.
+    radii = nsSize(radius, radius);
+    return MakeUnique<EllipseShapeInfo>(logicalCenter, radii, aShapeMargin);
+  }
+
+  MOZ_ASSERT(aBasicShape.IsEllipse());
+  nsSize physicalRadii = ShapeUtils::ComputeEllipseRadii(
+      aBasicShape, physicalCenter, physicalShapeBoxRect);
+  LogicalSize logicalRadii(aWM, physicalRadii);
+  radii = nsSize(logicalRadii.ISize(aWM), logicalRadii.BSize(aWM));
+
+  // If radii are close to the same value, or if aShapeMargin is small
+  // enough (as specified in css pixels), then we can use the three argument
+  // constructor for EllipseShapeInfo, which uses math for a more efficient
+  // method of float area computation.
+  if (EllipseShapeInfo::ShapeMarginIsNegligible(aShapeMargin) ||
+      EllipseShapeInfo::RadiiAreRoughlyEqual(radii)) {
+    return MakeUnique<EllipseShapeInfo>(logicalCenter, radii, aShapeMargin);
+  }
+
+  // We have to use the full constructor for EllipseShapeInfo. This
+  // computes the float area using a rasterization method.
+  nsDeviceContext* dc = aFrame->PresContext()->DeviceContext();
+  int32_t appUnitsPerDevPixel = dc->AppUnitsPerDevPixel();
+  return MakeUnique<EllipseShapeInfo>(logicalCenter, radii, aShapeMargin,
+                                      appUnitsPerDevPixel);
+}
+
+/* static */ UniquePtr<nsFloatManager::ShapeInfo>
+nsFloatManager::ShapeInfo::CreatePolygon(const StyleBasicShape& aBasicShape,
+                                         nscoord aShapeMargin,
+                                         nsIFrame* const aFrame,
+                                         const LogicalRect& aShapeBoxRect,
+                                         const LogicalRect& aMarginRect,
+                                         WritingMode aWM,
+                                         const nsSize& aContainerSize) {
+  // Use physical coordinates to compute each (xi, yi) vertex because CSS
+  // represents them using physical coordinates.
+  // https://drafts.csswg.org/css-shapes-1/#funcdef-polygon
+  nsRect physicalShapeBoxRect =
+      aShapeBoxRect.GetPhysicalRect(aWM, aContainerSize);
+
+  // Get physical vertices.
+  nsTArray<nsPoint> vertices =
+      ShapeUtils::ComputePolygonVertices(aBasicShape, physicalShapeBoxRect);
+
+  // Convert all the physical vertices to logical.
+  for (nsPoint& vertex : vertices) {
+    vertex = ConvertToFloatLogical(vertex, aWM, aContainerSize);
+  }
+
+  if (aShapeMargin == 0) {
+    return MakeUnique<PolygonShapeInfo>(std::move(vertices));
+  }
+
+  nsRect marginRect = ConvertToFloatLogical(aMarginRect, aWM, aContainerSize);
+
+  // We have to use the full constructor for PolygonShapeInfo. This
+  // computes the float area using a rasterization method.
+  int32_t appUnitsPerDevPixel = aFrame->PresContext()->AppUnitsPerDevPixel();
+  return MakeUnique<PolygonShapeInfo>(std::move(vertices), aShapeMargin,
+                                      appUnitsPerDevPixel, marginRect);
+}
+
+/* static */ UniquePtr<nsFloatManager::ShapeInfo>
+nsFloatManager::ShapeInfo::CreateImageShape(const StyleImage& aShapeImage,
+                                            float aShapeImageThreshold,
+                                            nscoord aShapeMargin,
+                                            nsIFrame* const aFrame,
+                                            const LogicalRect& aMarginRect,
+                                            WritingMode aWM,
+                                            const nsSize& aContainerSize) {
+  MOZ_ASSERT(&aShapeImage == &aFrame->StyleDisplay()->mShapeOutside.AsImage(),
+             "aFrame should be the frame that we got aShapeImage from");
+
+  nsImageRenderer imageRenderer(aFrame, &aShapeImage,
+                                nsImageRenderer::FLAG_SYNC_DECODE_IMAGES);
+
+  if (!imageRenderer.PrepareImage()) {
+    // The image is not ready yet.  Boost its loading priority since it will
+    // affect layout.
+    if (imgRequestProxy* req = aShapeImage.GetImageRequest()) {
+      req->BoostPriority(imgIRequest::CATEGORY_SIZE_QUERY);
+    }
+    return nullptr;
+  }
+
+  nsRect contentRect = aFrame->GetContentRect();
+
+  // Create a draw target and draw shape image on it.
+  nsDeviceContext* dc = aFrame->PresContext()->DeviceContext();
+  int32_t appUnitsPerDevPixel = dc->AppUnitsPerDevPixel();
+  LayoutDeviceIntSize contentSizeInDevPixels =
+      LayoutDeviceIntSize::FromAppUnitsRounded(contentRect.Size(),
+                                               appUnitsPerDevPixel);
+
+  // Use empty CSSSizeOrRatio to force set the preferred size as the frame's
+  // content box size.
+  imageRenderer.SetPreferredSize(CSSSizeOrRatio(), contentRect.Size());
+
+  RefPtr<gfx::DrawTarget> drawTarget =
+      gfxPlatform::GetPlatform()->CreateOffscreenCanvasDrawTarget(
+          contentSizeInDevPixels.ToUnknownSize(), gfx::SurfaceFormat::A8);
+  if (!drawTarget) {
+    return nullptr;
+  }
+
+  gfxContext context(drawTarget);
+
+  ImgDrawResult result =
+      imageRenderer.DrawShapeImage(aFrame->PresContext(), context);
+
+  if (result != ImgDrawResult::SUCCESS) {
+    return nullptr;
+  }
+
+  // Retrieve the pixel image buffer to create the image shape info.
+  RefPtr<SourceSurface> sourceSurface = drawTarget->Snapshot();
+  RefPtr<DataSourceSurface> dataSourceSurface = sourceSurface->GetDataSurface();
+  DataSourceSurface::ScopedMap map(dataSourceSurface, DataSourceSurface::READ);
+
+  if (!map.IsMapped()) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(sourceSurface->GetSize() == contentSizeInDevPixels.ToUnknownSize(),
+             "Who changes the size?");
+
+  nsRect marginRect = aMarginRect.GetPhysicalRect(aWM, aContainerSize);
+
+  uint8_t* alphaPixels = map.GetData();
+  int32_t stride = map.GetStride();
+
+  // NOTE: ImageShapeInfo constructor does not keep a persistent copy of
+  // alphaPixels; it's only used during the constructor to compute pixel ranges.
+  return MakeUnique<ImageShapeInfo>(alphaPixels, stride, contentSizeInDevPixels,
+                                    appUnitsPerDevPixel, aShapeImageThreshold,
+                                    aShapeMargin, contentRect, marginRect, aWM,
+                                    aContainerSize);
+}
+
+/* static */
+nscoord nsFloatManager::ShapeInfo::ComputeEllipseLineInterceptDiff(
+    const nscoord aShapeBoxBStart, const nscoord aShapeBoxBEnd,
+    const nscoord aBStartCornerRadiusL, const nscoord aBStartCornerRadiusB,
+    const nscoord aBEndCornerRadiusL, const nscoord aBEndCornerRadiusB,
+    const nscoord aBandBStart, const nscoord aBandBEnd) {
+  // An example for the band intersecting with the top right corner of an
+  // ellipse with writing-mode horizontal-tb.
+  //
+  //                             lineIntercept lineDiff
+  //                                    |       |
+  //  +---------------------------------|-------|-+---- aShapeBoxBStart
+  //  |                ##########^      |       | |
+  //  |            ##############|####  |       | |
+  //  +---------#################|######|-------|-+---- aBandBStart
+  //  |       ###################|######|##     | |
+  //  |     aBStartCornerRadiusB |######|###    | |
+  //  |    ######################|######|#####  | |
+  //  +---#######################|<-----------><->^---- aBandBEnd
+  //  |  ########################|##############  |
+  //  |  ########################|##############  |---- b
+  //  | #########################|############### |
+  //  | ######################## v<-------------->v
+  //  |###################### aBStartCornerRadiusL|
+  //  |###########################################|
+  //  |###########################################|
+  //  |###########################################|
+  //  |###########################################|
+  //  | ######################################### |
+  //  | ######################################### |
+  //  |  #######################################  |
+  //  |  #######################################  |
+  //  |   #####################################   |
+  //  |    ###################################    |
+  //  |      ###############################      |
+  //  |       #############################       |
+  //  |         #########################         |
+  //  |            ###################            |
+  //  |                ###########                |
+  //  +-------------------------------------------+----- aShapeBoxBEnd
+
+  NS_ASSERTION(aShapeBoxBStart <= aShapeBoxBEnd, "Bad shape box coordinates!");
+  NS_ASSERTION(aBandBStart <= aBandBEnd, "Bad band coordinates!");
+
+  nscoord lineDiff = 0;
+
+  // If the band intersects both the block-start and block-end corners, we
+  // don't need to enter either branch because the correct lineDiff is 0.
+  if (aBStartCornerRadiusB > 0 && aBandBEnd >= aShapeBoxBStart &&
+      aBandBEnd <= aShapeBoxBStart + aBStartCornerRadiusB) {
+    // The band intersects only the block-start corner.
+    nscoord b = aBStartCornerRadiusB - (aBandBEnd - aShapeBoxBStart);
+    nscoord lineIntercept =
+        XInterceptAtY(b, aBStartCornerRadiusL, aBStartCornerRadiusB);
+    lineDiff = aBStartCornerRadiusL - lineIntercept;
+  } else if (aBEndCornerRadiusB > 0 &&
+             aBandBStart >= aShapeBoxBEnd - aBEndCornerRadiusB &&
+             aBandBStart <= aShapeBoxBEnd) {
+    // The band intersects only the block-end corner.
+    nscoord b = aBEndCornerRadiusB - (aShapeBoxBEnd - aBandBStart);
+    nscoord lineIntercept =
+        XInterceptAtY(b, aBEndCornerRadiusL, aBEndCornerRadiusB);
+    lineDiff = aBEndCornerRadiusL - lineIntercept;
+  }
+
+  return lineDiff;
+}
+
+/* static */
+nscoord nsFloatManager::ShapeInfo::XInterceptAtY(const nscoord aY,
+                                                 const nscoord aRadiusX,
+                                                 const nscoord aRadiusY) {
+  // Solve for x in the ellipse equation (x/radiusX)^2 + (y/radiusY)^2 = 1.
+  MOZ_ASSERT(aRadiusY > 0);
+  const auto ratioY = aY / static_cast<double>(aRadiusY);
+  MOZ_ASSERT(ratioY <= 1, "Why is position y outside of the radius on y-axis?");
+  return NSToCoordTrunc(aRadiusX * std::sqrt(1 - ratioY * ratioY));
+}
+
+/* static */
+nsPoint nsFloatManager::ShapeInfo::ConvertToFloatLogical(
+    const nsPoint& aPoint, WritingMode aWM, const nsSize& aContainerSize) {
+  LogicalPoint logicalPoint(aWM, aPoint, aContainerSize);
+  return nsPoint(logicalPoint.LineRelative(aWM, aContainerSize),
+                 logicalPoint.B(aWM));
+}
+
+/* static */ UniquePtr<nscoord[]>
+nsFloatManager::ShapeInfo::ConvertToFloatLogical(const nscoord aRadii[8],
+                                                 WritingMode aWM) {
+  UniquePtr<nscoord[]> logicalRadii(new nscoord[8]);
+
+  // Get the physical side for line-left and line-right since border radii
+  // are on the physical axis.
+  Side lineLeftSide =
+      aWM.PhysicalSide(aWM.LogicalSideForLineRelativeDir(eLineRelativeDirLeft));
+  logicalRadii[eCornerTopLeftX] =
+      aRadii[SideToHalfCorner(lineLeftSide, true, false)];
+  logicalRadii[eCornerTopLeftY] =
+      aRadii[SideToHalfCorner(lineLeftSide, true, true)];
+  logicalRadii[eCornerBottomLeftX] =
+      aRadii[SideToHalfCorner(lineLeftSide, false, false)];
+  logicalRadii[eCornerBottomLeftY] =
+      aRadii[SideToHalfCorner(lineLeftSide, false, true)];
+
+  Side lineRightSide = aWM.PhysicalSide(
+      aWM.LogicalSideForLineRelativeDir(eLineRelativeDirRight));
+  logicalRadii[eCornerTopRightX] =
+      aRadii[SideToHalfCorner(lineRightSide, false, false)];
+  logicalRadii[eCornerTopRightY] =
+      aRadii[SideToHalfCorner(lineRightSide, false, true)];
+  logicalRadii[eCornerBottomRightX] =
+      aRadii[SideToHalfCorner(lineRightSide, true, false)];
+  logicalRadii[eCornerBottomRightY] =
+      aRadii[SideToHalfCorner(lineRightSide, true, true)];
+
+  if (aWM.IsLineInverted()) {
+    // When IsLineInverted() is true, i.e. aWM is vertical-lr,
+    // line-over/line-under are inverted from block-start/block-end. So the
+    // relationship reverses between which corner comes first going
+    // clockwise, and which corner is block-start versus block-end. We need
+    // to swap the values stored in top and bottom corners.
+    std::swap(logicalRadii[eCornerTopLeftX], logicalRadii[eCornerBottomLeftX]);
+    std::swap(logicalRadii[eCornerTopLeftY], logicalRadii[eCornerBottomLeftY]);
+    std::swap(logicalRadii[eCornerTopRightX],
+              logicalRadii[eCornerBottomRightX]);
+    std::swap(logicalRadii[eCornerTopRightY],
+              logicalRadii[eCornerBottomRightY]);
+  }
+
+  return logicalRadii;
+}
+
+/* static */
+size_t nsFloatManager::ShapeInfo::MinIntervalIndexContainingY(
+    const nsTArray<nsRect>& aIntervals, const nscoord aTargetY) {
+  // Perform a binary search to find the minimum index of an interval
+  // that contains aTargetY. If no such interval exists, return a value
+  // equal to the number of intervals.
+  size_t startIdx = 0;
+  size_t endIdx = aIntervals.Length();
+  while (startIdx < endIdx) {
+    size_t midIdx = startIdx + (endIdx - startIdx) / 2;
+    if (aIntervals[midIdx].ContainsY(aTargetY)) {
+      return midIdx;
+    }
+    nscoord midY = aIntervals[midIdx].Y();
+    if (midY < aTargetY) {
+      startIdx = midIdx + 1;
+    } else {
+      endIdx = midIdx;
+    }
+  }
+
+  return endIdx;
+}
+
+/* static */
+nscoord nsFloatManager::ShapeInfo::LineEdge(const nsTArray<nsRect>& aIntervals,
+                                            const nscoord aBStart,
+                                            const nscoord aBEnd,
+                                            bool aIsLineLeft) {
+  MOZ_ASSERT(aBStart <= aBEnd,
+             "The band's block start is greater than its block end?");
+
+  // Find all the intervals whose rects overlap the aBStart to
+  // aBEnd range, and find the most constraining inline edge
+  // depending on the value of aLeft.
+
+  // Since the intervals are stored in block-axis order, we need
+  // to find the first interval that overlaps aBStart and check
+  // succeeding intervals until we get past aBEnd.
+
+  nscoord lineEdge = aIsLineLeft ? nscoord_MAX : nscoord_MIN;
+
+  size_t intervalCount = aIntervals.Length();
+  for (size_t i = MinIntervalIndexContainingY(aIntervals, aBStart);
+       i < intervalCount; ++i) {
+    // We can always get the bCoord from the intervals' mLineLeft,
+    // since the y() coordinate is duplicated in both points in the
+    // interval.
+    auto& interval = aIntervals[i];
+    nscoord bCoord = interval.Y();
+    if (bCoord >= aBEnd) {
+      break;
+    }
+    // Get the edge from the interval point indicated by aLeft.
+    if (aIsLineLeft) {
+      lineEdge = std::min(lineEdge, interval.X());
+    } else {
+      lineEdge = std::max(lineEdge, interval.XMost());
+    }
+  }
+
+  return lineEdge;
+}
+
+/* static */ nsFloatManager::ShapeInfo::dfType
+nsFloatManager::ShapeInfo::CalcUsedShapeMargin5X(nscoord aShapeMargin,
+                                                 int32_t aAppUnitsPerDevPixel) {
+  // Our distance field has to be able to hold values equal to the
+  // maximum shape-margin value that we care about faithfully rendering,
+  // times 5. A 16-bit unsigned int can represent up to ~ 65K which means
+  // we can handle a margin up to ~ 13K device pixels. That's good enough
+  // for practical usage. Any supplied shape-margin value higher than this
+  // maximum will be clamped.
+  static const float MAX_MARGIN_5X_FLOAT = (float)MAX_MARGIN_5X;
+
+  // Convert aShapeMargin to dev pixels, convert that into 5x-dev-pixel
+  // space, then clamp to MAX_MARGIN_5X_FLOAT.
+  float shapeMarginDevPixels5X =
+      5.0f * NSAppUnitsToFloatPixels(aShapeMargin, aAppUnitsPerDevPixel);
+  NS_WARNING_ASSERTION(shapeMarginDevPixels5X <= MAX_MARGIN_5X_FLOAT,
+                       "shape-margin is too large and is being clamped.");
+
+  // We calculate a minimum in float space, which takes care of any overflow
+  // or infinity that may have occurred earlier from multiplication of
+  // too-large aShapeMargin values.
+  float usedMargin5XFloat =
+      std::min(shapeMarginDevPixels5X, MAX_MARGIN_5X_FLOAT);
+  return (dfType)NSToIntRound(usedMargin5XFloat);
+}
+
+//----------------------------------------------------------------------
+
+nsAutoFloatManager::~nsAutoFloatManager() {
+  // Restore the old float manager in the reflow input if necessary.
+  if (mNew) {
+#ifdef DEBUG
+    if (nsBlockFrame::gNoisyFloatManager) {
+      printf("restoring old float manager %p\n", mOld);
+    }
+#endif
+
+    mReflowInput.mFloatManager = mOld;
+
+#ifdef DEBUG
+    if (nsBlockFrame::gNoisyFloatManager) {
+      if (mOld) {
+        mReflowInput.mFrame->ListTag(stdout);
+        printf(": float manager %p after reflow\n", mOld);
+        mOld->List(stdout);
+      }
+    }
+#endif
+  }
+}
+
+void nsAutoFloatManager::CreateFloatManager(nsPresContext* aPresContext) {
+  MOZ_ASSERT(!mNew, "Redundant call to CreateFloatManager!");
+
+  // Create a new float manager and install it in the reflow
+  // input. `Remember' the old float manager so we can restore it
+  // later.
+  mNew = MakeUnique<nsFloatManager>(aPresContext->PresShell(),
+                                    mReflowInput.GetWritingMode());
+
+#ifdef DEBUG
+  if (nsBlockFrame::gNoisyFloatManager) {
+    printf("constructed new float manager %p (replacing %p)\n", mNew.get(),
+           mReflowInput.mFloatManager);
+  }
+#endif
+
+  // Set the float manager in the existing reflow input.
+  mOld = mReflowInput.mFloatManager;
+  mReflowInput.mFloatManager = mNew.get();
+}