Canvas2d: Implement rerouting event by hit region's control.

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

Index: third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
index 6fa3c4bcab02e1a7227a1e76db7dd89befcd5435..740ceffcd90f20cdb1ae5831561ac22ea4570a5d 100644
--- a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
@@ -33,6 +33,8 @@
 #include "core/HTMLNames.h"
 #include "core/dom/Document.h"
 #include "core/dom/ExceptionCode.h"
+#include "core/events/Event.h"
+#include "core/events/EventDispatcher.h"
 #include "core/fileapi/File.h"
 #include "core/frame/ImageBitmap.h"
 #include "core/frame/LocalFrame.h"
@@ -1018,4 +1020,14 @@ bool HTMLCanvasElement::isOpaque() const
     return m_context && !m_context->hasAlpha();
 }
 
+bool HTMLCanvasElement::dispatchEventInternal(PassRefPtrWillBeRawPtr<Event> event)

[philipj_slow, 2016/02/01 04:05:19]

Will this happen for both UA-created and script-created events? I'm trying to
understand how this will be expressed in the spec, and if this will really
correspond to patching hit testing, or if we're now inside DOM's
dispatchEvent().

[zino, 2016/02/05 06:59:48]

In the new patch set, I filtered script-created events out.
I think we avoid hit-testing in case of script-created events. (It can be
initialized from MouseEventInit dictionary).

+{
+    Node* target = nullptr;
+    if (m_context && m_context->is2d() && m_context->hitRegionsCount() > 0)
+        target = m_context->getControlAndUpdateEvent(*event);

[philipj_slow, 2016/02/01 04:05:19]

Might it be more clear to just return the target here and modify the event
outside of getControlAndUpdateEvent? I think so :)

[zino, 2016/02/05 06:59:48]

I agree with you but performance is also important.
So, I thought it is better to avoid to get hit-region if possible.
If we split the function into two parts(getControl and updateEvent), we will
have to get hit-region twice.
So, Instead, I introduced getControlAndIDIfHitRegionExists() in the new patch
set.

[philipj_slow, 2016/02/05 07:30:06]

Ack, std::pair looks like a nice fit.

+    if (!target)
+        target = this;

[philipj_slow, 2016/02/01 04:05:19]

Shouldn't this fall back to the parent class's dispatchEventInternal? Seems like
the easiest way to guarantee no change in behavior if there is no region.

[zino, 2016/02/05 06:59:48]

Sure!

Thank you.

Done.

+    return EventDispatcher::dispatchEvent(*target, event->createMediator());
+}
+
 } // namespace blink