Bug 1294351 - Move restoring the canvas clip stack to its own method and early return form EnsureTarget. r=Bas

dom/canvas/CanvasRenderingContext2D.cpp

@@ -1505,6 +1505,33 @@ CanvasRenderingContext2D::OnStableState()
   mHasPendingStableStateCallback = false;
 }
 
+void
+CanvasRenderingContext2D::RestoreClipsAndTransformToTarget()
+{
+  // Restore clips and transform.
+  mTarget->SetTransform(Matrix());
+
+  if (mTarget->GetBackendType() == gfx::BackendType::CAIRO) {
+    // Cairo doesn't play well with huge clips. When given a very big clip it
+    // will try to allocate big mask surface without taking the target
+    // size into account which can cause OOM. See bug 1034593.
+    // This limits the clip extents to the size of the canvas.
+    // A fix in Cairo would probably be preferable, but requires somewhat
+    // invasive changes.
+    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);
+      } else {
+        mTarget->SetTransform(clipOrTransform.transform);
+      }
+    }
+  }
+}
+
 CanvasRenderingContext2D::RenderingMode
 CanvasRenderingContext2D::EnsureTarget(const gfx::Rect* aCoveredRect,
                                        RenderingMode aRenderingMode)
@@ -1556,7 +1583,13 @@ CanvasRenderingContext2D::EnsureTarget(const gfx::Rect* aCoveredRect,
                                            : IntRect(0, 0, mWidth, mHeight);
     mTarget = mBufferProvider->BorrowDrawTarget(persistedRect);
 
-    mode = mRenderingMode;
+    if (mTarget && !mBufferProvider->PreservesDrawingState()) {
+      RestoreClipsAndTransformToTarget();
+    }
+
+    if (mTarget) {
+      return mode;
+    }
   }
 
   mIsSkiaGL = false;
@@ -1649,28 +1682,7 @@ CanvasRenderingContext2D::EnsureTarget(const gfx::Rect* aCoveredRect,
 
     if (mBufferProvider != oldBufferProvider || !mBufferProvider ||
         !mBufferProvider->PreservesDrawingState()) {
-      // Restore clips and transform.
-      mTarget->SetTransform(Matrix());
-
-      if (mTarget->GetBackendType() == gfx::BackendType::CAIRO) {
-        // Cairo doesn't play well with huge clips. When given a very big clip it
-        // will try to allocate big mask surface without taking the target
-        // size into account which can cause OOM. See bug 1034593.
-        // This limits the clip extents to the size of the canvas.
-        // A fix in Cairo would probably be preferable, but requires somewhat
-        // invasive changes.
-        mTarget->PushClipRect(canvasRect);
-      }
-
-      for (const auto& style : mStyleStack) {
-        for (const auto& clipOrTransform : style.clipsAndTransforms) {
-          if (clipOrTransform.IsClip()) {
-            mTarget->PushClip(clipOrTransform.clip);
-          } else {
-            mTarget->SetTransform(clipOrTransform.transform);
-          }
-        }
-      }
+      RestoreClipsAndTransformToTarget();
     }
   } else {
     EnsureErrorTarget();
@@ -1792,7 +1804,7 @@ CanvasRenderingContext2D::ReturnTarget(bool aForceReset)
 
       if (mTarget->GetBackendType() == gfx::BackendType::CAIRO) {
         // With the cairo backend we pushed an extra clip rect which we have to
-        // balance out here. See the comment in EnsureDrawTarget.
+        // balance out here. See the comment in RestoreClipsAndTransformToTarget.
         mTarget->PopClip();
       }
     }

dom/canvas/CanvasRenderingContext2D.h

@@ -643,6 +643,8 @@ protected:
   RenderingMode EnsureTarget(const gfx::Rect* aCoveredRect = nullptr,
                              RenderingMode aRenderMode = RenderingMode::DefaultBackendMode);
 
+  void RestoreClipsAndTransformToTarget();
+
   /**
    * This method is run at the end of the event-loop spin where
    * ScheduleStableStateCallback was called.