Bug 980207 - When the refresh driver is under test control, make compositor thread only update when a composite is scheduled; r=dzbarsky

In order to make test behavior better match real-world sampling behavior, this
patch updates the test code in CompositorParent so that it only updates the
layer when a composite is scheduled. This enables creating mochitests that
reproduce bugs observed in regular usage.

gfx/layers/ipc/CompositorParent.cpp

@@ -330,8 +330,7 @@ CompositorParent::RecvFlushRendering()
   // If we're waiting to do a composite, then cancel it
   // and do it immediately instead.
   if (mCurrentCompositeTask) {
-    mCurrentCompositeTask->Cancel();
-    mCurrentCompositeTask = nullptr;
+    CancelCurrentCompositeTask();
     ForceComposeToTarget(nullptr);
   }
   return true;
@@ -376,9 +375,15 @@ CompositorParent::RecvSetTestSampleTime(const TimeStamp& aTime)
 
   mIsTesting = true;
   mTestTime = aTime;
-  if (mCompositionManager) {
-    mCompositionManager->TransformShadowTree(aTime);
+
+  // Update but only if we were already scheduled to animate
+  if (mCompositionManager && mCurrentCompositeTask) {
+    bool requestNextFrame = mCompositionManager->TransformShadowTree(aTime);
+    if (!requestNextFrame) {
+      CancelCurrentCompositeTask();
+    }
   }
+
   return true;
 }
 
@@ -464,6 +469,15 @@ CompositorParent::ForceComposition()
   ScheduleRenderOnCompositorThread();
 }
 
+void
+CompositorParent::CancelCurrentCompositeTask()
+{
+  if (mCurrentCompositeTask) {
+    mCurrentCompositeTask->Cancel();
+    mCurrentCompositeTask = nullptr;
+  }
+}
+
 void
 CompositorParent::SetEGLSurfaceSize(int width, int height)
 {
@@ -757,12 +771,22 @@ CompositorParent::ShadowLayersUpdated(LayerTransactionParent* aLayerTree,
 
   if (root) {
     SetShadowProperties(root);
-    if (mIsTesting) {
-      mCompositionManager->TransformShadowTree(mTestTime);
-    }
   }
   if (aScheduleComposite) {
     ScheduleComposition();
+    // When testing we synchronously update the shadow tree with the animated
+    // values to avoid race conditions when calling GetAnimationTransform etc.
+    // (since the above SetShadowProperties will remove animation effects).
+    // However, we only do this update when a composite operation is already
+    // scheduled in order to better match the behavior under regular sampling
+    // conditions.
+    if (mIsTesting && root && mCurrentCompositeTask) {
+      bool requestNextFrame =
+        mCompositionManager->TransformShadowTree(mTestTime);
+      if (!requestNextFrame) {
+        CancelCurrentCompositeTask();
+      }
+    }
   }
   mLayerManager->NotifyShadowTreeTransaction();
 }

gfx/layers/ipc/CompositorParent.h

@@ -249,6 +249,7 @@ private:
   void ResumeComposition();
   void ResumeCompositionAndResize(int width, int height);
   void ForceComposition();
+  void CancelCurrentCompositeTask();
 
   inline static PlatformThreadId CompositorThreadID();