1 files changed, 95 insertions, 0 deletions
diff --git a/gfx/layers/apz/src/SampledAPZCState.cpp b/gfx/layers/apz/src/SampledAPZCState.cpp
new file mode 100644
index 0000000000..b90f60d4e0
--- /dev/null
+++ b/gfx/layers/apz/src/SampledAPZCState.cpp
@@ -0,0 +1,95 @@
+/* -*- 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 "SampledAPZCState.h"
+#include "APZUtils.h"
+
+namespace mozilla {
+namespace layers {
+
+SampledAPZCState::SampledAPZCState() {}
+
+SampledAPZCState::SampledAPZCState(const FrameMetrics& aMetrics)
+    : mLayoutViewport(aMetrics.GetLayoutViewport()),
+      mVisualScrollOffset(aMetrics.GetVisualScrollOffset()),
+      mZoom(aMetrics.GetZoom()) {
+  RemoveFractionalAsyncDelta();
+}
+
+SampledAPZCState::SampledAPZCState(const FrameMetrics& aMetrics,
+                                   Maybe<CompositionPayload>&& aPayload)
+    : mLayoutViewport(aMetrics.GetLayoutViewport()),
+      mVisualScrollOffset(aMetrics.GetVisualScrollOffset()),
+      mZoom(aMetrics.GetZoom()),
+      mScrollPayload(std::move(aPayload)) {
+  RemoveFractionalAsyncDelta();
+}
+
+bool SampledAPZCState::operator==(const SampledAPZCState& aOther) const {
+  // The payload doesn't factor into equality, that just comes along for
+  // the ride.
+  return mLayoutViewport.IsEqualEdges(aOther.mLayoutViewport) &&
+         mVisualScrollOffset == aOther.mVisualScrollOffset &&
+         mZoom == aOther.mZoom;
+}
+
+bool SampledAPZCState::operator!=(const SampledAPZCState& aOther) const {
+  return !(*this == aOther);
+}
+
+Maybe<CompositionPayload> SampledAPZCState::TakeScrollPayload() {
+  return std::move(mScrollPayload);
+}
+
+void SampledAPZCState::UpdateScrollProperties(const FrameMetrics& aMetrics) {
+  mLayoutViewport = aMetrics.GetLayoutViewport();
+  mVisualScrollOffset = aMetrics.GetVisualScrollOffset();
+}
+
+void SampledAPZCState::UpdateZoomProperties(const FrameMetrics& aMetrics) {
+  mZoom = aMetrics.GetZoom();
+}
+
+void SampledAPZCState::ClampVisualScrollOffset(const FrameMetrics& aMetrics) {
+  mVisualScrollOffset =
+      aMetrics.CalculateScrollRange().ClampPoint(mVisualScrollOffset);
+  FrameMetrics::KeepLayoutViewportEnclosingVisualViewport(
+      CSSRect(mVisualScrollOffset,
+              aMetrics.CalculateCompositedSizeInCssPixels()),
+      aMetrics.GetScrollableRect(), mLayoutViewport);
+}
+
+void SampledAPZCState::ZoomBy(const gfxSize& aScale) {
+  mZoom.xScale *= aScale.width;
+  mZoom.yScale *= aScale.height;
+}
+
+void SampledAPZCState::RemoveFractionalAsyncDelta() {
+  // This function is a performance hack. With non-WebRender, having small
+  // fractional deltas between the layout offset and scroll offset on
+  // container layers can trigger the creation of a temporary surface during
+  // composition, because it produces a non-integer translation that doesn't
+  // play well with layer clips. So we detect the case where the delta is
+  // uselessly small (0.01 parentlayer pixels or less) and tweak the sampled
+  // scroll offset to eliminate it. By doing this here at sample time rather
+  // than elsewhere in the pipeline we are least likely to break assumptions
+  // and invariants elsewhere in the code, since sampling effectively takes
+  // a snapshot of APZ state (decoupling it from APZ assumptions) and provides
+  // it as an input to the compositor (so all compositor state should be
+  // internally consistent based on this input).
+  if (mLayoutViewport.TopLeft() == mVisualScrollOffset) {
+    return;
+  }
+  ParentLayerPoint paintedOffset = mLayoutViewport.TopLeft() * mZoom;
+  ParentLayerPoint asyncOffset = mVisualScrollOffset * mZoom;
+  if (FuzzyEqualsAdditive(paintedOffset.x, asyncOffset.x, COORDINATE_EPSILON) &&
+      FuzzyEqualsAdditive(paintedOffset.y, asyncOffset.y, COORDINATE_EPSILON)) {
+    mVisualScrollOffset = mLayoutViewport.TopLeft();
+  }
+}
+
+}  // namespace layers
+}  // namespace mozilla