Bug 1531417 - enable shared buffer provider for software canvas on all platforms. r=nical

dom/canvas/CanvasRenderingContext2D.cpp

@@ -1355,6 +1355,13 @@ bool CanvasRenderingContext2D::TrySharedTarget(
     return false;
   }
 
+#ifdef XP_WIN
+  // Bug 1285271 - Disable shared buffer provider on Windows with D2D due to instability
+  if (gfxPlatform::GetPlatform()->GetPreferredCanvasBackend() == BackendType::DIRECT2D1_1) {
+    return false;
+  }
+#endif
+
   RefPtr<LayerManager> layerManager =
       LayerManagerFromCanvasElement(mCanvasElement);
 
@@ -4557,7 +4564,10 @@ void CanvasRenderingContext2D::DrawWindow(nsGlobalWindowInner& aWindow,
   CompositionOp op = UsedOperation();
   bool discardContent =
       GlobalAlpha() == 1.0f &&
-      (op == CompositionOp::OP_OVER || op == CompositionOp::OP_SOURCE);
+      (op == CompositionOp::OP_OVER || op == CompositionOp::OP_SOURCE) &&
+      (!mBufferProvider ||
+        (mBufferProvider->GetType() != LayersBackend::LAYERS_CLIENT &&
+         mBufferProvider->GetType() != LayersBackend::LAYERS_WR));
   const gfx::Rect drawRect(aX, aY, aW, aH);
   EnsureTarget(discardContent ? &drawRect : nullptr);
   if (!IsTargetValid()) {

modules/libpref/init/all.js

@@ -5082,15 +5082,6 @@ pref("layers.prefer-opengl", false);
 // Copy-on-write canvas
 pref("layers.shared-buffer-provider.enabled", true);
 
-#ifdef XP_WIN
-pref("layers.shared-buffer-provider.enabled", false);
-#endif
-
-#ifdef XP_MACOSX
-// cf. Bug 1324908
-pref("layers.shared-buffer-provider.enabled", false);
-#endif
-
 // Force all possible layers to be always active layers
 pref("layers.force-active", false);