1 files changed, 118 insertions, 0 deletions
diff --git a/gfx/layers/apz/src/APZUtils.cpp b/gfx/layers/apz/src/APZUtils.cpp
new file mode 100644
index 0000000000..843046c34a
--- /dev/null
+++ b/gfx/layers/apz/src/APZUtils.cpp
@@ -0,0 +1,118 @@
+/* -*- 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 "mozilla/layers/APZUtils.h"
+
+#include "mozilla/StaticPrefs_apz.h"
+#include "mozilla/StaticPrefs_layers.h"
+
+namespace mozilla {
+namespace layers {
+
+namespace apz {
+
+bool IsCloseToHorizontal(float aAngle, float aThreshold) {
+  return (aAngle < aThreshold || aAngle > (M_PI - aThreshold));
+}
+
+bool IsCloseToVertical(float aAngle, float aThreshold) {
+  return (fabs(aAngle - (M_PI / 2)) < aThreshold);
+}
+
+bool IsStuckAtBottom(gfxFloat aTranslation,
+                     const LayerRectAbsolute& aInnerRange,
+                     const LayerRectAbsolute& aOuterRange) {
+  // The item will be stuck at the bottom if the async scroll delta is in
+  // the range [aOuterRange.Y(), aInnerRange.Y()]. Since the translation
+  // is negated with repect to the async scroll delta (i.e. scrolling down
+  // produces a positive scroll delta and negative translation), we invert it
+  // and check to see if it falls in the specified range.
+  return aOuterRange.Y() <= -aTranslation && -aTranslation <= aInnerRange.Y();
+}
+
+bool IsStuckAtTop(gfxFloat aTranslation, const LayerRectAbsolute& aInnerRange,
+                  const LayerRectAbsolute& aOuterRange) {
+  // Same as IsStuckAtBottom, except we want to check for the range
+  // [aInnerRange.YMost(), aOuterRange.YMost()].
+  return aInnerRange.YMost() <= -aTranslation &&
+         -aTranslation <= aOuterRange.YMost();
+}
+
+ScreenPoint ComputeFixedMarginsOffset(
+    const ScreenMargin& aCompositorFixedLayerMargins, SideBits aFixedSides,
+    const ScreenMargin& aGeckoFixedLayerMargins) {
+  // Work out the necessary translation, in screen space.
+  ScreenPoint translation;
+
+  ScreenMargin effectiveMargin =
+      aCompositorFixedLayerMargins - aGeckoFixedLayerMargins;
+  if ((aFixedSides & SideBits::eLeftRight) == SideBits::eLeftRight) {
+    translation.x += (effectiveMargin.left - effectiveMargin.right) / 2;
+  } else if (aFixedSides & SideBits::eRight) {
+    translation.x -= effectiveMargin.right;
+  } else if (aFixedSides & SideBits::eLeft) {
+    translation.x += effectiveMargin.left;
+  }
+
+  if ((aFixedSides & SideBits::eTopBottom) == SideBits::eTopBottom) {
+    translation.y += (effectiveMargin.top - effectiveMargin.bottom) / 2;
+  } else if (aFixedSides & SideBits::eBottom) {
+    translation.y -= effectiveMargin.bottom;
+  } else if (aFixedSides & SideBits::eTop) {
+    translation.y += effectiveMargin.top;
+  }
+
+  return translation;
+}
+
+bool AboutToCheckerboard(const FrameMetrics& aPaintedMetrics,
+                         const FrameMetrics& aCompositorMetrics) {
+  // The main-thread code to compute the painted area can introduce some
+  // rounding error due to multiple unit conversions, so we inflate the rect by
+  // one app unit to account for that.
+  CSSRect painted = aPaintedMetrics.GetDisplayPort() +
+                    aPaintedMetrics.GetLayoutScrollOffset();
+  painted.Inflate(CSSMargin::FromAppUnits(nsMargin(1, 1, 1, 1)));
+
+  // Inflate the rect by the danger zone. See the description of the danger zone
+  // prefs in AsyncPanZoomController.cpp for an explanation of this.
+  CSSRect visible =
+      CSSRect(aCompositorMetrics.GetVisualScrollOffset(),
+              aCompositorMetrics.CalculateBoundedCompositedSizeInCssPixels());
+  visible.Inflate(ScreenSize(StaticPrefs::apz_danger_zone_x(),
+                             StaticPrefs::apz_danger_zone_y()) /
+                  aCompositorMetrics.DisplayportPixelsPerCSSPixel());
+
+  // Clamp both rects to the scrollable rect, because having either of those
+  // exceed the scrollable rect doesn't make sense, and could lead to false
+  // positives.
+  painted = painted.Intersect(aPaintedMetrics.GetScrollableRect());
+  visible = visible.Intersect(aPaintedMetrics.GetScrollableRect());
+
+  return !painted.Contains(visible);
+}
+
+SideBits GetOverscrollSideBits(const ParentLayerPoint& aOverscrollAmount) {
+  SideBits sides = SideBits::eNone;
+
+  if (aOverscrollAmount.x < 0) {
+    sides |= SideBits::eLeft;
+  } else if (aOverscrollAmount.x > 0) {
+    sides |= SideBits::eRight;
+  }
+
+  if (aOverscrollAmount.y < 0) {
+    sides |= SideBits::eTop;
+  } else if (aOverscrollAmount.y > 0) {
+    sides |= SideBits::eBottom;
+  }
+
+  return sides;
+}
+
+}  // namespace apz
+}  // namespace layers
+}  // namespace mozilla