Add touchpad pinch zoom support to Blink

Source/web/WebViewImpl.cpp

 /*
  * Copyright (C) 2011, 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 2126 matching lines @@
             eventType, static_cast<const WebMouseEvent&>(inputEvent).clickCount);
         return true;
     }
 
     // FIXME: This should take in the intended frame, not the local frame root.
     if (PageWidgetDelegate::handleInputEvent(*this, inputEvent, localFrameRootTemporary()->frame()))
         return true;
 
     // Unhandled touchpad gesture pinch events synthesize mouse wheel events.
     if (inputEvent.type == WebInputEvent::GesturePinchUpdate) {
-        if (handleSyntheticWheelFromTouchpadPinchEvent(static_cast<const WebGestureEvent&>(inputEvent)))
+        const WebGestureEvent& pinchEvent = static_cast<const WebGestureEvent&>(inputEvent);
+        // First, synthesize a Windows-like wheel event to send to any handlers that may exist.
+        if (handleSyntheticWheelFromTouchpadPinchEvent(pinchEvent))
             return true;
+
+        // If the event remains unhandled, use it pinch the viewport.
+        const float magnifyDelta = pinchEvent.data.pinchUpdate.scale;
+        const float oldPageScale = pageScaleFactor();
+        setPageScaleFactor(oldPageScale * magnifyDelta);

[aelias_OOO_until_Jul13, 2015/01/30 21:21:40]

Please avoid this call to setPageScaleFactor, since setting scale and scroll in
separate calls can sometimes cause subtle clamping bugs.  Instead, you can do
"float newPageScale = clampPageScaleFactorToLimits(oldPageScale *
magnifyDelta())", then call pinchViewport.setScaleAndLocation() instead of
move().

[ccameron, 2015/02/02 23:59:07]

Done.

+        const float newPageScale = pageScaleFactor();
+
+        // Keep the center-of-pinch anchor specified by (x, y) in a stable
+        // position over the course of the magnify.
+        const FloatPoint anchor(pinchEvent.x, pinchEvent.y);
+        FloatPoint anchorAtOldScale = anchor.scaledBy(1.f / oldPageScale);
+        FloatPoint anchorAtNewScale = anchor.scaledBy(1.f / newPageScale);
+        FloatSize anchorDelta = anchorAtOldScale - anchorAtNewScale;
+        page()->frameHost().pinchViewport().move(FloatPoint(anchorDelta.width(), anchorDelta.height()));
+
+        // TODO(ccameron): Always return that the event was handled. Once the pinch-zoom content scale
+        // handlers have been remove from content, this function may return false if the page scale does
+        // not change.
+        return true;
     }
 
     return false;
 }
 
 void WebViewImpl::setCursorVisibilityState(bool isVisible)
 {
     if (m_page)
         m_page->setIsCursorVisible(isVisible);
 }
@@ skipping 2451 matching lines @@
     return mainFrameImpl()->frameView()->layoutSize().width() == m_size.width
         || (constraints.minimumScale == constraints.maximumScale && constraints.minimumScale != -1);
 }
 
 void WebViewImpl::forceNextWebGLContextCreationToFail()
 {
     WebGLRenderingContext::forceNextWebGLContextCreationToFail();
 }
 
 } // namespace blink