1 files changed, 90 insertions, 0 deletions
diff --git a/layout/generic/ReflowOutput.cpp b/layout/generic/ReflowOutput.cpp
new file mode 100644
index 0000000000..a0312dffda
--- /dev/null
+++ b/layout/generic/ReflowOutput.cpp
@@ -0,0 +1,90 @@
+/* -*- 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/. */
+
+/* struct containing the output from nsIFrame::Reflow */
+
+#include "mozilla/ReflowOutput.h"
+#include "mozilla/ReflowInput.h"
+
+namespace mozilla {
+
+static bool IsValidOverflowRect(const nsRect& aRect) {
+  // `IsEmpty` in the context of `nsRect` means "width OR height is zero."
+  // However, in the context of overflow, the rect having one axis as zero is
+  // NOT considered empty.
+  if (MOZ_LIKELY(!aRect.IsEmpty())) {
+    return true;
+  }
+
+  // Be defensive and consider rects with any negative size as invalid.
+  return !aRect.IsEqualEdges(nsRect()) && aRect.Width() >= 0 &&
+         aRect.Height() >= 0;
+}
+
+/* static */
+nsRect OverflowAreas::GetOverflowClipRect(const nsRect& aRectToClip,
+                                          const nsRect& aBounds,
+                                          PhysicalAxes aClipAxes,
+                                          const nsSize& aOverflowMargin) {
+  auto inflatedBounds = aBounds;
+  inflatedBounds.Inflate(aOverflowMargin);
+  auto clip = aRectToClip;
+  if (aClipAxes & PhysicalAxes::Vertical) {
+    clip.y = inflatedBounds.y;
+    clip.height = inflatedBounds.height;
+  }
+  if (aClipAxes & PhysicalAxes::Horizontal) {
+    clip.x = inflatedBounds.x;
+    clip.width = inflatedBounds.width;
+  }
+  return clip;
+}
+
+/* static */
+void OverflowAreas::ApplyOverflowClippingOnRect(nsRect& aOverflowRect,
+                                                const nsRect& aBounds,
+                                                PhysicalAxes aClipAxes,
+                                                const nsSize& aOverflowMargin) {
+  aOverflowRect = aOverflowRect.Intersect(
+      GetOverflowClipRect(aOverflowRect, aBounds, aClipAxes, aOverflowMargin));
+}
+
+void OverflowAreas::UnionWith(const OverflowAreas& aOther) {
+  if (IsValidOverflowRect(aOther.InkOverflow())) {
+    InkOverflow().UnionRect(InkOverflow(), aOther.InkOverflow());
+  }
+  if (IsValidOverflowRect(aOther.ScrollableOverflow())) {
+    ScrollableOverflow().UnionRect(ScrollableOverflow(),
+                                   aOther.ScrollableOverflow());
+  }
+}
+
+void OverflowAreas::UnionAllWith(const nsRect& aRect) {
+  if (!IsValidOverflowRect(aRect)) {
+    // Same as `UnionWith()` - avoid losing information.
+    return;
+  }
+  InkOverflow().UnionRect(InkOverflow(), aRect);
+  ScrollableOverflow().UnionRect(ScrollableOverflow(), aRect);
+}
+
+void OverflowAreas::SetAllTo(const nsRect& aRect) {
+  InkOverflow() = aRect;
+  ScrollableOverflow() = aRect;
+}
+
+ReflowOutput::ReflowOutput(const ReflowInput& aReflowInput)
+    : ReflowOutput(aReflowInput.GetWritingMode()) {}
+
+void ReflowOutput::SetOverflowAreasToDesiredBounds() {
+  mOverflowAreas.SetAllTo(nsRect(0, 0, Width(), Height()));
+}
+
+void ReflowOutput::UnionOverflowAreasWithDesiredBounds() {
+  mOverflowAreas.UnionAllWith(nsRect(0, 0, Width(), Height()));
+}
+
+}  // namespace mozilla