Refactor CRC2D::reset() to avoid non-additive SkCanvas state operations

third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2D.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc.
  * All rights reserved.
  * Copyright (C) 2008, 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  * Copyright (C) 2012, 2013 Intel Corporation. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
@@ skipping 140 matching lines @@
 }
 
 CanvasRenderingContext2D::~CanvasRenderingContext2D() {}
 
 void CanvasRenderingContext2D::dispose() {
   if (m_pruneLocalFontCacheScheduled)
     Platform::current()->currentThread()->removeTaskObserver(this);
 }
 
 void CanvasRenderingContext2D::validateStateStack() const {
-#if ENABLE(ASSERT)
-  SkCanvas* skCanvas = canvas()->existingDrawingCanvas();
-  if (skCanvas && m_contextLostMode == NotLostContext) {
-    ASSERT(static_cast<size_t>(skCanvas->getSaveCount()) ==
-           m_stateStack.size());
+#if DCHECK_IS_ON()
+  if (SkCanvas* skCanvas = canvas()->existingDrawingCanvas()) {
+    // The canvas should always have an initial save frame, to support
+    // resetting the top level matrix and clip.
+    DCHECK_GT(skCanvas->getSaveCount(), 1);
+
+    if (m_contextLostMode == NotLostContext) {
+      DCHECK_EQ(static_cast<size_t>(skCanvas->getSaveCount()),
+                m_stateStack.size() + 1);
+    }
   }
 #endif
   CHECK(m_stateStack.first()
             .get());  // Temporary for investigating crbug.com/648510
 }
 
 bool CanvasRenderingContext2D::isAccelerated() const {
   if (!canvas()->hasImageBuffer())
     return false;
   return canvas()->buffer()->isAccelerated();
@@ skipping 96 matching lines @@
     canvas()->dispatchEvent(event);
   }
 }
 
 void CanvasRenderingContext2D::reset() {
   validateStateStack();
   unwindStateStack();
   m_stateStack.resize(1);
   m_stateStack.first() = CanvasRenderingContext2DState::create();
   m_path.clear();
-  SkCanvas* c = canvas()->existingDrawingCanvas();
-  if (c) {
-    c->resetMatrix();
-    c->clipRect(SkRect::MakeWH(canvas()->width(), canvas()->height()),
-                SkRegion::kReplace_Op);
+  if (SkCanvas* c = canvas()->existingDrawingCanvas()) {
+    // The canvas should always have an initial/unbalanced save frame, which
+    // we use to reset the top level matrix and clip here.
+    DCHECK_EQ(c->getSaveCount(), 2);
+    c->restore();
+    c->save();
+    DCHECK(c->getTotalMatrix().isIdentity());
+#if DCHECK_IS_ON()
+    SkIRect clipBounds;
+    DCHECK(c->getClipDeviceBounds(&clipBounds));
+    DCHECK(clipBounds == c->imageInfo().bounds());
+#endif
   }
   validateStateStack();
 }
 
 void CanvasRenderingContext2D::restoreCanvasMatrixClipStack(SkCanvas* c) const {
   restoreMatrixClipStack(c);
 }
 
 bool CanvasRenderingContext2D::shouldAntialias() const {
   return state().shouldAntialias();
@@ skipping 831 matching lines @@
   }
   return true;
 }
 
 void CanvasRenderingContext2D::resetUsageTracking() {
   UsageCounters newCounters;
   m_usageCounters = newCounters;
 }
 
 }  // namespace blink