Canvas2d: The control in hit region should be a canvas fallback element.

third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp

 /*
  * Copyright (C) 2004, 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 13 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "core/html/HTMLCanvasElement.h"
 
 #include "bindings/core/v8/ExceptionMessages.h"
 #include "bindings/core/v8/ExceptionState.h"
 #include "bindings/core/v8/ScriptController.h"
 #include "core/HTMLNames.h"
+#include "core/InputTypeNames.h"
 #include "core/dom/Document.h"
+#include "core/dom/Element.h"
+#include "core/dom/ElementTraversal.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/fileapi/File.h"
 #include "core/frame/ImageBitmap.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
+#include "core/html/HTMLImageElement.h"
+#include "core/html/HTMLInputElement.h"
+#include "core/html/HTMLSelectElement.h"
 #include "core/html/ImageData.h"
 #include "core/html/canvas/CanvasAsyncBlobCreator.h"
 #include "core/html/canvas/CanvasContextCreationAttributes.h"
 #include "core/html/canvas/CanvasFontCache.h"
 #include "core/html/canvas/CanvasRenderingContext.h"
 #include "core/html/canvas/CanvasRenderingContextFactory.h"
 #include "core/imagebitmap/ImageBitmapOptions.h"
 #include "core/layout/LayoutHTMLCanvas.h"
 #include "core/paint/PaintLayer.h"
 #include "platform/Histogram.h"
@@ skipping 974 matching lines @@
         return ScriptPromise();
     }
     return ImageBitmapSource::fulfillImageBitmap(scriptState, isPaintable() ? ImageBitmap::create(this, IntRect(sx, sy, sw, sh), options) : nullptr);
 }
 
 bool HTMLCanvasElement::isOpaque() const
 {
     return m_context && !m_context->hasAlpha();
 }
 
+bool HTMLCanvasElement::isSupportedInteractiveCanvasFallback(const Element& element)
+{
+    if (!element.isDescendantOf(this))
+        return false;
+
+    if (element.hasTagName(HTMLNames::aTag))

[Justin Novosad, 2016/02/12 15:10:45]

You should use the helpers (isHTMLAnchorElement) instead of calling hasTagName
directly. Same for other instances below.

[zino, 2016/02/12 16:40:34]

Done.

+        return !Traversal<HTMLImageElement>::firstWithin(element);

[Justin Novosad, 2016/02/12 15:10:45]

Please add a comment to explain this.

[zino, 2016/02/12 16:40:34]

Done.

+
+    if (element.hasTagName(HTMLNames::buttonTag))

[Justin Novosad, 2016/02/12 15:10:45]

Could be "else if". Same thing for "if" statements below.

[zino, 2016/02/12 16:40:34]

As far as I know, we don't use "else if" in Blink.
I'm not sure but the blink coding style[1] is still saying like that.

[1] Line breaking-"3":
https://www.chromium.org/blink/coding-style#TOC-Line-breaking

+        return true;
+
+    if (element.hasTagName(HTMLNames::inputTag)) {
+        const HTMLInputElement& inputElement = toHTMLInputElement(element);
+        if (inputElement.type() == InputTypeNames::checkbox || inputElement.type() == InputTypeNames::radio
+            || (inputElement.isTextButton() && !inputElement.isImage()))

[Justin Novosad, 2016/02/12 15:10:45]

Why do you need to check !inputElement.isImage()? Can an inputElement be a text
button and an image at the same time? It does not look that way from reading the
code of the various InputType classes.

[zino, 2016/02/12 16:40:34]

Done.

+            return true;
+    }
+
+    if (element.hasTagName(HTMLNames::selectTag)) {
+        const HTMLSelectElement& selectElement = toHTMLSelectElement(element);
+        if (selectElement.multiple() || selectElement.size() > 1)
+            return true;
+    }
+
+    if (isHTMLOptionElement(element) && element.parentNode() && isHTMLSelectElement(*element.parentNode())) {
+        const HTMLSelectElement& selectElement = toHTMLSelectElement(*element.parentNode());
+        if (selectElement.multiple() || selectElement.size() > 1)

[Justin Novosad, 2016/02/12 15:10:45]

Add a comment to explain this condition.

[zino, 2016/02/12 16:40:34]

Done.

+            return true;
+    }
+
+    if (element.fastHasAttribute(HTMLNames::tabindexAttr))
+        return true;
+
+    if (element.hasTagName(HTMLNames::tableTag)
+        || element.hasTagName(HTMLNames::captionTag)
+        || element.hasTagName(HTMLNames::theadTag)
+        || element.hasTagName(HTMLNames::tbodyTag)
+        || element.hasTagName(HTMLNames::tfootTag)
+        || element.hasTagName(HTMLNames::trTag)
+        || element.hasTagName(HTMLNames::tdTag)
+        || element.hasTagName(HTMLNames::thTag))
+        return true;
+
+    return false;
+}
+
 } // namespace blink