Make OffscreenCanvas resizeable

third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/offscreencanvas/OffscreenCanvas.h"
 
 #include "core/dom/ExceptionCode.h"
 #include "core/fileapi/Blob.h"
 #include "core/html/ImageData.h"
 #include "core/html/canvas/CanvasAsyncBlobCreator.h"
@@ skipping 11 matching lines @@
 namespace blink {
 
 OffscreenCanvas::OffscreenCanvas(const IntSize& size)
     : m_size(size), m_originClean(true) {}
 
 OffscreenCanvas* OffscreenCanvas::create(unsigned width, unsigned height) {
   return new OffscreenCanvas(
       IntSize(clampTo<int>(width), clampTo<int>(height)));
 }
 
-void OffscreenCanvas::setWidth(unsigned width, ExceptionState& exceptionState) {
-  // If this OffscreenCanvas is transferred control by an html canvas,
-  // its size is determined by html canvas's size and cannot be resized.
-  if (hasPlaceholderCanvas()) {
-    exceptionState.throwDOMException(InvalidStateError,
-                                     "Resizing is not allowed on an "
-                                     "OffscreenCanvas that has been "
-                                     "transferred control from a canvas.");
-    return;
-  }
-  m_size.setWidth(clampTo<int>(width));
+void OffscreenCanvas::setWidth(unsigned width) {
+  IntSize newSize = m_size;
+  newSize.setWidth(clampTo<int>(width));
+  setSize(newSize);
 }
 
-void OffscreenCanvas::setHeight(unsigned height,
-                                ExceptionState& exceptionState) {
-  // Same comment as above.
-  if (hasPlaceholderCanvas()) {
-    exceptionState.throwDOMException(InvalidStateError,
-                                     "Resizing is not allowed on an "
-                                     "OffscreenCanvas that has been "
-                                     "transferred control from a canvas.");
-    return;
+void OffscreenCanvas::setHeight(unsigned height) {
+  IntSize newSize = m_size;
+  newSize.setHeight(clampTo<int>(height));
+  setSize(newSize);
+}
+
+void OffscreenCanvas::setSize(const IntSize& size) {

[xidachen, 2016/11/17 02:12:22]

OK, I am a little confused here. The logic here sounds perfectly correct.
However, when I look at HTMLCanvasElement::setSize(), the function is not
getting called by setWidth() or setHeight(). That means setWidth() and
setHeight() in HTMLCanvasElement doesn't really do anything to its context, is
my understanding correct?

+  if (m_context) {
+    if (m_context->is3d()) {
+      if (size != m_size)
+        m_context->reshape(size.width(), size.height());
+    } else if (m_context->is2d()) {
+      m_context->reset();
+    }
   }
-  m_size.setHeight(clampTo<int>(height));
+  m_size = size;
 }
 
 void OffscreenCanvas::setNeutered() {
   ASSERT(!m_context);
   m_isNeutered = true;
   m_size.setWidth(0);
   m_size.setHeight(0);
 }
 
 ImageBitmap* OffscreenCanvas::transferToImageBitmap(
@@ skipping 171 matching lines @@
   return resolver->promise();
 }
 
 DEFINE_TRACE(OffscreenCanvas) {
   visitor->trace(m_context);
   visitor->trace(m_executionContext);
   EventTarget::trace(visitor);
 }
 
 }  // namespace blink