1 files changed, 130 insertions, 0 deletions
diff --git a/gfx/layers/apz/src/SmoothMsdScrollAnimation.cpp b/gfx/layers/apz/src/SmoothMsdScrollAnimation.cpp
new file mode 100644
index 0000000000..ab57f345da
--- /dev/null
+++ b/gfx/layers/apz/src/SmoothMsdScrollAnimation.cpp
@@ -0,0 +1,130 @@
+/* -*- 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 "SmoothMsdScrollAnimation.h"
+#include "AsyncPanZoomController.h"
+
+namespace mozilla {
+namespace layers {
+
+SmoothMsdScrollAnimation::SmoothMsdScrollAnimation(
+    AsyncPanZoomController& aApzc, const CSSPoint& aInitialPosition,
+    const CSSPoint& aInitialVelocity, const CSSPoint& aDestination,
+    double aSpringConstant, double aDampingRatio)
+    : mApzc(aApzc),
+      mXAxisModel(aInitialPosition.x, aDestination.x, aInitialVelocity.x,
+                  aSpringConstant, aDampingRatio),
+      mYAxisModel(aInitialPosition.y, aDestination.y, aInitialVelocity.y,
+                  aSpringConstant, aDampingRatio) {}
+
+bool SmoothMsdScrollAnimation::DoSample(FrameMetrics& aFrameMetrics,
+                                        const TimeDuration& aDelta) {
+  CSSToParentLayerScale2D zoom = aFrameMetrics.GetZoom();
+  if (zoom == CSSToParentLayerScale2D(0, 0)) {
+    return false;
+  }
+  CSSPoint oneParentLayerPixel =
+      ParentLayerPoint(1, 1) / aFrameMetrics.GetZoom();
+  if (mXAxisModel.IsFinished(oneParentLayerPixel.x) &&
+      mYAxisModel.IsFinished(oneParentLayerPixel.y)) {
+    // Set the scroll offset to the exact destination. If we allow the scroll
+    // offset to end up being a bit off from the destination, we can get
+    // artefacts like "scroll to the next snap point in this direction"
+    // scrolling to the snap point we're already supposed to be at.
+    mApzc.ClampAndSetVisualScrollOffset(
+        CSSPoint(mXAxisModel.GetDestination(), mYAxisModel.GetDestination()));
+    return false;
+  }
+
+  mXAxisModel.Simulate(aDelta);
+  mYAxisModel.Simulate(aDelta);
+
+  CSSPoint position =
+      CSSPoint(mXAxisModel.GetPosition(), mYAxisModel.GetPosition());
+  CSSPoint css_velocity =
+      CSSPoint(mXAxisModel.GetVelocity(), mYAxisModel.GetVelocity());
+
+  // Convert from pixels/second to pixels/ms
+  ParentLayerPoint velocity =
+      ParentLayerPoint(css_velocity.x, css_velocity.y) / 1000.0f;
+
+  // Keep the velocity updated for the Axis class so that any animations
+  // chained off of the smooth scroll will inherit it.
+  if (mXAxisModel.IsFinished(oneParentLayerPixel.x)) {
+    mApzc.mX.SetVelocity(0);
+  } else {
+    mApzc.mX.SetVelocity(velocity.x);
+  }
+  if (mYAxisModel.IsFinished(oneParentLayerPixel.y)) {
+    mApzc.mY.SetVelocity(0);
+  } else {
+    mApzc.mY.SetVelocity(velocity.y);
+  }
+  // If we overscroll, hand off to a fling animation that will complete the
+  // spring back.
+  ParentLayerPoint displacement =
+      (position - aFrameMetrics.GetVisualScrollOffset()) * zoom;
+
+  ParentLayerPoint overscroll;
+  ParentLayerPoint adjustedOffset;
+  mApzc.mX.AdjustDisplacement(displacement.x, adjustedOffset.x, overscroll.x);
+  mApzc.mY.AdjustDisplacement(displacement.y, adjustedOffset.y, overscroll.y);
+  mApzc.ScrollBy(adjustedOffset / zoom);
+  // The smooth scroll may have caused us to reach the end of our scroll
+  // range. This can happen if either the
+  // layout.css.scroll-behavior.damping-ratio preference is set to less than 1
+  // (underdamped) or if a smooth scroll inherits velocity from a fling
+  // gesture.
+  if (!IsZero(overscroll)) {
+    // Hand off a fling with the remaining momentum to the next APZC in the
+    // overscroll handoff chain.
+
+    // We may have reached the end of the scroll range along one axis but
+    // not the other. In such a case we only want to hand off the relevant
+    // component of the fling.
+    if (FuzzyEqualsAdditive(overscroll.x, 0.0f, COORDINATE_EPSILON)) {
+      velocity.x = 0;
+    } else if (FuzzyEqualsAdditive(overscroll.y, 0.0f, COORDINATE_EPSILON)) {
+      velocity.y = 0;
+    }
+
+    // To hand off the fling, we attempt to find a target APZC and start a new
+    // fling with the same velocity on that APZC. For simplicity, the actual
+    // overscroll of the current sample is discarded rather than being handed
+    // off. The compositor should sample animations sufficiently frequently
+    // that this is not noticeable. The target APZC is chosen by seeing if
+    // there is an APZC further in the handoff chain which is pannable; if
+    // there isn't, we take the new fling ourselves, entering an overscrolled
+    // state.
+    // Note: APZC is holding mRecursiveMutex, so directly calling
+    // HandleSmoothScrollOverscroll() (which acquires the tree lock) would
+    // violate the lock ordering. Instead we schedule
+    // HandleSmoothScrollOverscroll() to be called after mRecursiveMutex is
+    // released.
+    mDeferredTasks.AppendElement(NewRunnableMethod<ParentLayerPoint>(
+        "layers::AsyncPanZoomController::HandleSmoothScrollOverscroll", &mApzc,
+        &AsyncPanZoomController::HandleSmoothScrollOverscroll, velocity));
+    return false;
+  }
+
+  return true;
+}
+
+void SmoothMsdScrollAnimation::SetDestination(const CSSPoint& aNewDestination) {
+  mXAxisModel.SetDestination(aNewDestination.x);
+  mYAxisModel.SetDestination(aNewDestination.y);
+}
+
+CSSPoint SmoothMsdScrollAnimation::GetDestination() const {
+  return CSSPoint(mXAxisModel.GetDestination(), mYAxisModel.GetDestination());
+}
+
+SmoothMsdScrollAnimation*
+SmoothMsdScrollAnimation::AsSmoothMsdScrollAnimation() {
+  return this;
+}
+
+}  // namespace layers
+}  // namespace mozilla