Bug 1572415: Convert clip paths when potentially changing canvas backend in CanvasRenderingContext2D. r=jrmuizel

The clip Paths in mStyleStack might not be compatible with the new mTarget, so
this converts them to make sure they are.

Differential Revision: https://phabricator.services.mozilla.com/D51668

--HG--
extra : moz-landing-system : lando

dom/canvas/CanvasRenderingContext2D.cpp

@@ -1221,15 +1221,25 @@ void CanvasRenderingContext2D::RestoreClipsAndTransformToTarget() {
     mTarget->PushClipRect(gfx::Rect(0, 0, mWidth, mHeight));
   }
 
-  for (const auto& style : mStyleStack) {
-    for (const auto& clipOrTransform : style.clipsAndTransforms) {
-      if (clipOrTransform.IsClip()) {
-        mTarget->PushClip(clipOrTransform.clip);
+  for (auto& style : mStyleStack) {
+    for (auto clipOrTransform = style.clipsAndTransforms.begin();
+         clipOrTransform != style.clipsAndTransforms.end(); clipOrTransform++) {
+      if (clipOrTransform->IsClip()) {
+        if (mClipsNeedConverting) {
+          // We have possibly changed backends, so we need to convert the clips
+          // in case they are no longer compatible with mTarget.
+          RefPtr<PathBuilder> pathBuilder = mTarget->CreatePathBuilder();
+          clipOrTransform->clip->StreamToSink(pathBuilder);
+          clipOrTransform->clip = pathBuilder->Finish();
+        }
+        mTarget->PushClip(clipOrTransform->clip);
       } else {
-        mTarget->SetTransform(clipOrTransform.transform);
+        mTarget->SetTransform(clipOrTransform->transform);
       }
     }
   }
+
+  mClipsNeedConverting = false;
 }
 
 bool CanvasRenderingContext2D::EnsureTarget(const gfx::Rect* aCoveredRect,
@@ -1419,6 +1429,7 @@ bool CanvasRenderingContext2D::TrySharedTarget(
     // we are already using a shared buffer provider, we are allocating a new
     // one because the current one failed so let's just fall back to the basic
     // provider.
+    mClipsNeedConverting = true;
     return false;
   }
 

dom/canvas/CanvasRenderingContext2D.h

@@ -1041,6 +1041,7 @@ class CanvasRenderingContext2D final : public nsICanvasRenderingContextInternal,
   bool IsWriteOnly() const { return mWriteOnly; }
 
   bool mWriteOnly;
+  bool mClipsNeedConverting = false;
 };
 
 size_t BindingJSObjectMallocBytes(CanvasRenderingContext2D* aContext);