1 files changed, 376 insertions, 0 deletions
diff --git a/gfx/layers/apz/util/DoubleTapToZoom.cpp b/gfx/layers/apz/util/DoubleTapToZoom.cpp
new file mode 100644
index 0000000000..c40d79ced3
--- /dev/null
+++ b/gfx/layers/apz/util/DoubleTapToZoom.cpp
@@ -0,0 +1,376 @@
+/* -*- 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/. */
+
+#include "DoubleTapToZoom.h"
+
+#include <algorithm>  // for std::min, std::max
+
+#include "mozilla/PresShell.h"
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/dom/Element.h"
+#include "nsCOMPtr.h"
+#include "nsIContent.h"
+#include "mozilla/dom/Document.h"
+#include "nsIFrame.h"
+#include "nsIFrameInlines.h"
+#include "nsIScrollableFrame.h"
+#include "nsTableCellFrame.h"
+#include "nsLayoutUtils.h"
+#include "nsStyleConsts.h"
+#include "mozilla/ViewportUtils.h"
+#include "mozilla/EventListenerManager.h"
+
+namespace mozilla {
+namespace layers {
+
+namespace {
+
+using FrameForPointOption = nsLayoutUtils::FrameForPointOption;
+
+static bool IsGeneratedContent(nsIContent* aContent) {
+  // We exclude marks because making them double tap targets does not seem
+  // desirable.
+  return aContent->IsGeneratedContentContainerForBefore() ||
+         aContent->IsGeneratedContentContainerForAfter();
+}
+
+// Returns the DOM element found at |aPoint|, interpreted as being relative to
+// the root frame of |aPresShell| in visual coordinates. If the point is inside
+// a subdocument, returns an element inside the subdocument, rather than the
+// subdocument element (and does so recursively). The implementation was adapted
+// from DocumentOrShadowRoot::ElementFromPoint(), with the notable exception
+// that we don't pass nsLayoutUtils::IGNORE_CROSS_DOC to GetFrameForPoint(), so
+// as to get the behaviour described above in the presence of subdocuments.
+static already_AddRefed<dom::Element> ElementFromPoint(
+    const RefPtr<PresShell>& aPresShell, const CSSPoint& aPoint) {
+  nsIFrame* rootFrame = aPresShell->GetRootFrame();
+  if (!rootFrame) {
+    return nullptr;
+  }
+  nsIFrame* frame = nsLayoutUtils::GetFrameForPoint(
+      RelativeTo{rootFrame, ViewportType::Visual}, CSSPoint::ToAppUnits(aPoint),
+      {{FrameForPointOption::IgnorePaintSuppression}});
+  while (frame && (!frame->GetContent() ||
+                   (frame->GetContent()->IsInNativeAnonymousSubtree() &&
+                    !IsGeneratedContent(frame->GetContent())))) {
+    frame = nsLayoutUtils::GetParentOrPlaceholderFor(frame);
+  }
+  if (!frame) {
+    return nullptr;
+  }
+  // FIXME(emilio): This should probably use the flattened tree, GetParent() is
+  // not guaranteed to be an element in presence of shadow DOM.
+  nsIContent* content = frame->GetContent();
+  if (!content) {
+    return nullptr;
+  }
+  if (dom::Element* element = content->GetAsElementOrParentElement()) {
+    return do_AddRef(element);
+  }
+  return nullptr;
+}
+
+// Get table cell from element, parent or grand parent.
+static dom::Element* GetNearbyTableCell(
+    const nsCOMPtr<dom::Element>& aElement) {
+  nsTableCellFrame* tableCell = do_QueryFrame(aElement->GetPrimaryFrame());
+  if (tableCell) {
+    return aElement.get();
+  }
+  if (dom::Element* parent = aElement->GetFlattenedTreeParentElement()) {
+    nsTableCellFrame* tableCell = do_QueryFrame(parent->GetPrimaryFrame());
+    if (tableCell) {
+      return parent;
+    }
+    if (dom::Element* grandParent = parent->GetFlattenedTreeParentElement()) {
+      tableCell = do_QueryFrame(grandParent->GetPrimaryFrame());
+      if (tableCell) {
+        return grandParent;
+      }
+    }
+  }
+  return nullptr;
+}
+
+static bool ShouldZoomToElement(
+    const nsCOMPtr<dom::Element>& aElement,
+    const RefPtr<dom::Document>& aRootContentDocument,
+    nsIScrollableFrame* aRootScrollFrame, const FrameMetrics& aMetrics) {
+  if (nsIFrame* frame = aElement->GetPrimaryFrame()) {
+    if (frame->StyleDisplay()->IsInlineFlow() &&
+        // Replaced elements are suitable zoom targets because they act like
+        // inline-blocks instead of inline. (textarea's are the specific reason
+        // we do this)
+        !frame->IsFrameOfType(nsIFrame::eReplaced)) {
+      return false;
+    }
+  }
+  // Trying to zoom to the html element will just end up scrolling to the start
+  // of the document, return false and we'll run out of elements and just
+  // zoomout (without scrolling to the start).
+  if (aElement->OwnerDoc() == aRootContentDocument &&
+      aElement->IsHTMLElement(nsGkAtoms::html)) {
+    return false;
+  }
+  if (aElement->IsAnyOfHTMLElements(nsGkAtoms::li, nsGkAtoms::q)) {
+    return false;
+  }
+
+  // Ignore elements who are table cells or their parents are table cells, and
+  // they take up less than 30% of page rect width because they are likely cells
+  // in data tables (as opposed to tables used for layout purposes), and we
+  // don't want to zoom to them. This heuristic is quite naive and leaves a lot
+  // to be desired.
+  if (dom::Element* tableCell = GetNearbyTableCell(aElement)) {
+    CSSRect rect =
+        nsLayoutUtils::GetBoundingContentRect(tableCell, aRootScrollFrame);
+    if (rect.width < 0.3 * aMetrics.GetScrollableRect().width) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+// Calculates if zooming to aRect would have almost the same zoom level as
+// aCompositedArea currently has. If so we would want to zoom out instead.
+static bool RectHasAlmostSameZoomLevel(const CSSRect& aRect,
+                                       const CSSRect& aCompositedArea) {
+  // This functions checks to see if the area of the rect visible in the
+  // composition bounds (i.e. the overlapArea variable below) is approximately
+  // the max area of the rect we can show.
+
+  // AsyncPanZoomController::ZoomToRect will adjust the zoom and scroll offset
+  // so that the zoom to rect fills the composited area. If after adjusting the
+  // scroll offset _only_ the rect would fill the composited area we want to
+  // zoom out (we don't want to _just_ scroll, we want to do some amount of
+  // zooming, either in or out it doesn't matter which). So translate both rects
+  // to the same origin and then compute their overlap, which is what the
+  // following calculation does.
+
+  float overlapArea = std::min(aRect.width, aCompositedArea.width) *
+                      std::min(aRect.height, aCompositedArea.height);
+  float availHeight = std::min(
+      aRect.Width() * aCompositedArea.Height() / aCompositedArea.Width(),
+      aRect.Height());
+  float showing = overlapArea / (aRect.Width() * availHeight);
+  float ratioW = aRect.Width() / aCompositedArea.Width();
+  float ratioH = aRect.Height() / aCompositedArea.Height();
+
+  return showing > 0.9 && (ratioW > 0.9 || ratioH > 0.9);
+}
+
+}  // namespace
+
+static CSSRect AddHMargin(const CSSRect& aRect, const CSSCoord& aMargin,
+                          const FrameMetrics& aMetrics) {
+  CSSRect rect =
+      CSSRect(std::max(aMetrics.GetScrollableRect().X(), aRect.X() - aMargin),
+              aRect.Y(), aRect.Width() + 2 * aMargin, aRect.Height());
+  // Constrict the rect to the screen's right edge
+  rect.SetWidth(
+      std::min(rect.Width(), aMetrics.GetScrollableRect().XMost() - rect.X()));
+  return rect;
+}
+
+static CSSRect AddVMargin(const CSSRect& aRect, const CSSCoord& aMargin,
+                          const FrameMetrics& aMetrics) {
+  CSSRect rect =
+      CSSRect(aRect.X(),
+              std::max(aMetrics.GetScrollableRect().Y(), aRect.Y() - aMargin),
+              aRect.Width(), aRect.Height() + 2 * aMargin);
+  // Constrict the rect to the screen's bottom edge
+  rect.SetHeight(
+      std::min(rect.Height(), aMetrics.GetScrollableRect().YMost() - rect.Y()));
+  return rect;
+}
+
+static bool IsReplacedElement(const nsCOMPtr<dom::Element>& aElement) {
+  if (nsIFrame* frame = aElement->GetPrimaryFrame()) {
+    if (frame->IsFrameOfType(nsIFrame::eReplaced)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool HasNonPassiveWheelListenerOnAncestor(nsIContent* aContent) {
+  for (nsIContent* content = aContent; content;
+       content = content->GetFlattenedTreeParent()) {
+    EventListenerManager* elm = content->GetExistingListenerManager();
+    if (elm && elm->HasNonPassiveWheelListener()) {
+      return true;
+    }
+  }
+  return false;
+}
+
+ZoomTarget CalculateRectToZoomTo(
+    const RefPtr<dom::Document>& aRootContentDocument, const CSSPoint& aPoint) {
+  // Ensure the layout information we get is up-to-date.
+  aRootContentDocument->FlushPendingNotifications(FlushType::Layout);
+
+  // An empty rect as return value is interpreted as "zoom out".
+  const CSSRect zoomOut;
+
+  RefPtr<PresShell> presShell = aRootContentDocument->GetPresShell();
+  if (!presShell) {
+    return ZoomTarget{zoomOut, CantZoomOutBehavior::ZoomIn};
+  }
+
+  nsIScrollableFrame* rootScrollFrame =
+      presShell->GetRootScrollFrameAsScrollable();
+  if (!rootScrollFrame) {
+    return ZoomTarget{zoomOut, CantZoomOutBehavior::ZoomIn};
+  }
+
+  CSSPoint documentRelativePoint =
+      CSSPoint::FromAppUnits(ViewportUtils::VisualToLayout(
+          CSSPoint::ToAppUnits(aPoint), presShell)) +
+      CSSPoint::FromAppUnits(rootScrollFrame->GetScrollPosition());
+
+  nsCOMPtr<dom::Element> element = ElementFromPoint(presShell, aPoint);
+  if (!element) {
+    return ZoomTarget{zoomOut, CantZoomOutBehavior::ZoomIn, Nothing(),
+                      Some(documentRelativePoint)};
+  }
+
+  CantZoomOutBehavior cantZoomOutBehavior =
+      HasNonPassiveWheelListenerOnAncestor(element)
+          ? CantZoomOutBehavior::Nothing
+          : CantZoomOutBehavior::ZoomIn;
+
+  FrameMetrics metrics =
+      nsLayoutUtils::CalculateBasicFrameMetrics(rootScrollFrame);
+
+  while (element && !ShouldZoomToElement(element, aRootContentDocument,
+                                         rootScrollFrame, metrics)) {
+    element = element->GetFlattenedTreeParentElement();
+  }
+
+  if (!element) {
+    return ZoomTarget{zoomOut, cantZoomOutBehavior, Nothing(),
+                      Some(documentRelativePoint)};
+  }
+
+  CSSPoint visualScrollOffset = metrics.GetVisualScrollOffset();
+  CSSRect compositedArea(visualScrollOffset,
+                         metrics.CalculateCompositedSizeInCssPixels());
+  Maybe<CSSRect> nearestScrollClip;
+  CSSRect rect = nsLayoutUtils::GetBoundingContentRect(element, rootScrollFrame,
+                                                       &nearestScrollClip);
+
+  // In some cases, like overflow: visible and overflowing content, the bounding
+  // client rect of the targeted element won't contain the point the user double
+  // tapped on. In that case we use the scrollable overflow rect if it contains
+  // the user point.
+  if (!rect.Contains(documentRelativePoint)) {
+    if (nsIFrame* scrolledFrame = rootScrollFrame->GetScrolledFrame()) {
+      if (nsIFrame* f = element->GetPrimaryFrame()) {
+        nsRect overflowRect = f->ScrollableOverflowRect();
+        nsLayoutUtils::TransformResult res =
+            nsLayoutUtils::TransformRect(f, scrolledFrame, overflowRect);
+        MOZ_ASSERT(res == nsLayoutUtils::TRANSFORM_SUCCEEDED ||
+                   res == nsLayoutUtils::NONINVERTIBLE_TRANSFORM);
+        if (res == nsLayoutUtils::TRANSFORM_SUCCEEDED) {
+          CSSRect overflowRectCSS = CSSRect::FromAppUnits(overflowRect);
+          if (nearestScrollClip.isSome()) {
+            overflowRectCSS = nearestScrollClip->Intersect(overflowRectCSS);
+          }
+          if (overflowRectCSS.Contains(documentRelativePoint)) {
+            rect = overflowRectCSS;
+          }
+        }
+      }
+    }
+  }
+
+  CSSRect elementBoundingRect = rect;
+
+  // Generally we zoom to the width of some element, but sometimes we zoom to
+  // the height. We set this to true when that happens so that we can add a
+  // vertical margin to the rect, otherwise it looks weird.
+  bool heightConstrained = false;
+
+  // If the element is taller than the visible area of the page scale
+  // the height of the |rect| so that it has the same aspect ratio as
+  // the root frame.  The clipped |rect| is centered on the y value of
+  // the touch point. This allows tall narrow elements to be zoomed.
+  if (!rect.IsEmpty() && compositedArea.Width() > 0.0f &&
+      compositedArea.Height() > 0.0f) {
+    // Calculate the height of the rect if it had the same aspect ratio as
+    // compositedArea.
+    const float widthRatio = rect.Width() / compositedArea.Width();
+    float targetHeight = compositedArea.Height() * widthRatio;
+
+    // We don't want to cut off the top or bottoms of replaced elements that are
+    // square or wider in aspect ratio.
+
+    // If it's a replaced element and we would otherwise trim it's height below
+    if (IsReplacedElement(element) && targetHeight < rect.Height() &&
+        // If the target rect is at most 1.1x away from being square or wider
+        // aspect ratio
+        rect.Height() < 1.1 * rect.Width() &&
+        // and our compositedArea is wider than it is tall
+        compositedArea.Width() >= compositedArea.Height()) {
+      heightConstrained = true;
+      // Expand the width of the rect so that it fills compositedArea so that if
+      // we are already zoomed to this element then the IsRectZoomedIn call
+      // below returns true so that we zoom out. This won't change what we
+      // actually zoom to as we are just making the rect the same aspect ratio
+      // as compositedArea.
+      float targetWidth =
+          rect.Height() * compositedArea.Width() / compositedArea.Height();
+      MOZ_ASSERT(targetWidth > rect.Width());
+      if (targetWidth > rect.Width()) {
+        rect.x -= (targetWidth - rect.Width()) / 2;
+        rect.SetWidth(targetWidth);
+        // keep elementBoundingRect containing rect
+        elementBoundingRect = rect;
+      }
+
+    } else if (targetHeight < rect.Height()) {
+      // Trim the height so that the target rect has the same aspect ratio as
+      // compositedArea, centering it around the user tap point.
+      float newY = documentRelativePoint.y - (targetHeight * 0.5f);
+      if ((newY + targetHeight) > rect.YMost()) {
+        rect.MoveByY(rect.Height() - targetHeight);
+      } else if (newY > rect.Y()) {
+        rect.MoveToY(newY);
+      }
+      rect.SetHeight(targetHeight);
+    }
+  }
+
+  const CSSCoord margin = 15;
+  rect = AddHMargin(rect, margin, metrics);
+
+  if (heightConstrained) {
+    rect = AddVMargin(rect, margin, metrics);
+  }
+
+  // If the rect is already taking up most of the visible area and is
+  // stretching the width of the page, then we want to zoom out instead.
+  if (RectHasAlmostSameZoomLevel(rect, compositedArea)) {
+    return ZoomTarget{zoomOut, cantZoomOutBehavior, Nothing(),
+                      Some(documentRelativePoint)};
+  }
+
+  elementBoundingRect = AddHMargin(elementBoundingRect, margin, metrics);
+
+  // Unlike rect, elementBoundingRect is the full height of the element we are
+  // zooming to. If we zoom to it without a margin it can look a weird, so give
+  // it a vertical margin.
+  elementBoundingRect = AddVMargin(elementBoundingRect, margin, metrics);
+
+  rect.Round();
+  elementBoundingRect.Round();
+  return ZoomTarget{rect, cantZoomOutBehavior, Some(elementBoundingRect),
+                    Some(documentRelativePoint)};
+}
+
+}  // namespace layers
+}  // namespace mozilla