Initial draft - modify ViewportAnchor to know about both inner and outer viewports.

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 1671 matching lines @@
 
     bool shouldAnchorAndRescaleViewport = settings()->mainFrameResizesAreOrientationChanges()
         && m_size.width && contentsSize().width() && newSize.width != m_size.width && !m_fullscreenController->isFullscreen();
     float oldPageScaleFactor = pageScaleFactor();
     float oldMinimumPageScaleFactor = minimumPageScaleFactor();
 
     m_size = newSize;
 
     ViewportAnchor viewportAnchor(&localFrameRootTemporary()->frame()->eventHandler());
     if (shouldAnchorAndRescaleViewport) {
-        viewportAnchor.setAnchor(view->visibleContentRect(),
-                                 FloatSize(viewportAnchorXCoord, viewportAnchorYCoord));
+        viewportAnchor.setAnchor(
+            view->visibleContentRect(),
+            visibleRectInDocument(),
+            FloatSize(viewportAnchorXCoord, viewportAnchorYCoord));
     }
 
     // FIXME: TextAutosizer does not yet support out-of-process frames.
     if (mainFrameImpl() && mainFrameImpl()->frame()->isLocalFrame())
     {
         // Avoids unnecessary invalidations while various bits of state in TextAutosizer are updated.
         TextAutosizer::DeferUpdatePageInfo deferUpdatePageInfo(page());
         performResize();
     } else {
         performResize();
     }
 
     if (settings()->viewportEnabled() && !m_fixedLayoutSizeLock) {
         // Relayout immediately to recalculate the minimum scale limit.
         if (view->needsLayout())
             view->layout();
 
         if (shouldAnchorAndRescaleViewport) {
             float newPageScaleFactor = oldPageScaleFactor / oldMinimumPageScaleFactor * minimumPageScaleFactor();
-            IntSize scaledViewportSize = newSize;
-            scaledViewportSize.scale(1 / newPageScaleFactor);
-            setPageScaleFactor(newPageScaleFactor, viewportAnchor.computeOrigin(scaledViewportSize));
+            newPageScaleFactor = clampPageScaleFactorToLimits(newPageScaleFactor);
+
+            FloatSize pinchViewportSize = FloatSize(newSize);

[aelias_OOO_until_Jul13, 2014/09/17 05:16:36]

nit: second FloatSize() shouldn't be necessary, please delete it. 
initialization "=" is shorthand for constructor invocation, if I recall my C++
correctly.

[timav, 2014/09/17 17:54:45]

The cast is required to convert WebSize -> IntSize -> FloatSize, I guess C++
does implicit conversions only if there is a direct path from A to B.
IntSize() works here too, but compiler complains if there is no cast at all.

+            pinchViewportSize.scale(1 / newPageScaleFactor);
+
+            IntPoint mainFrameOrigin;
+            FloatPoint pinchViewportOrigin;
+            viewportAnchor.computeOrigins(*view, pinchViewportSize,
+                &mainFrameOrigin, &pinchViewportOrigin);
+            scrollAndRescaleViewports(newPageScaleFactor, mainFrameOrigin, pinchViewportOrigin);
         }
     }
 
     sendResizeEventAndRepaint();
 }
 
+IntRect WebViewImpl::visibleRectInDocument() const
+{
+    if (pinchVirtualViewportEnabled()) {
+        // Inner viewport in the document coordinates
+        return enclosedIntRect(page()->frameHost().pinchViewport().visibleRectInDocument());
+    }
+
+    // Outer viewport in the document coordinates
+    return localFrameRootTemporary()->frameView()->visibleContentRect();
+}
+
 void WebViewImpl::willEndLiveResize()
 {
     if (mainFrameImpl() && mainFrameImpl()->frameView())
         mainFrameImpl()->frameView()->willEndLiveResize();
 
     LocalFrame* frame = mainFrameImpl()->frame();
     WebPluginContainerImpl* pluginContainer = WebLocalFrameImpl::pluginContainerFromFrame(frame);
     if (pluginContainer)
         pluginContainer->willEndLiveResize();
 }
@@ skipping 1179 matching lines @@
 WebFloatPoint WebViewImpl::pinchViewportOffset() const
 {
     ASSERT(page());
 
     if (!pinchVirtualViewportEnabled())
         return WebFloatPoint();
 
     return page()->frameHost().pinchViewport().visibleRect().location();
 }
 
+void WebViewImpl::scrollAndRescaleViewports(float scaleFactor,
+    const IntPoint & mainFrameOrigin,

[aelias_OOO_until_Jul13, 2014/09/17 05:16:36]

nit: "IntPoint& mainFrameOrigin" (no space before)

[timav, 2014/09/17 17:54:45]

Done.

+    const FloatPoint & pinchViewportOrigin)
+{
+    // Old way
+    if (!pinchVirtualViewportEnabled()) {
+        setPageScaleFactor(scaleFactor, mainFrameOrigin);
+        return;
+    }
+
+    if (!page())
+        return;
+
+    if (!mainFrameImpl())
+        return;
+
+    FrameView * view = mainFrameImpl()->frameView();
+    if (!view)
+        return;
+
+    // Order is important: pinch viewport location is clamped based on
+    // main frame scroll position and pinch viewport scale.
+
+    // Set outer viewport position.

[aelias_OOO_until_Jul13, 2014/09/17 05:16:36]

Please delete the three comments starting here.  But it's fine to keep the
"Order is important" comment.

[timav, 2014/09/17 17:54:45]

Done.

+    view->setScrollOffset(mainFrameOrigin);
+
+    // Set the scale.
+    setPageScaleFactor(scaleFactor);
+
+    // Set inner viewport position.
+    page()->frameHost().pinchViewport().setLocation(pinchViewportOrigin);
+}
+
 void WebViewImpl::setPageScaleFactor(float scaleFactor)
 {
     ASSERT(page());
 
     scaleFactor = clampPageScaleFactorToLimits(scaleFactor);
     if (scaleFactor == pageScaleFactor())
         return;
 
     // TODO(bokan): Old-style pinch path. Remove when we're migrated to
     // virtual viewport pinch.
@@ skipping 22 matching lines @@
     newScrollOffset = clampOffsetAtScale(newScrollOffset, scaleFactor);
 
     if (pinchVirtualViewportEnabled())
         setPageScaleFactor(scaleFactor);
         // Note, we don't set the offset in the new path. This method is going
         // away for the new pinch model so that's ok.
     else
         page()->setPageScaleFactor(scaleFactor, newScrollOffset);
 }
 
-

[aelias_OOO_until_Jul13, 2014/09/17 05:16:36]

nit: unnecessary newline

[timav, 2014/09/17 17:54:45]

Newline removed in the new version.

 float WebViewImpl::deviceScaleFactor() const
 {
     if (!page())
         return 1;
 
     return page()->deviceScaleFactor();
 }
 
 void WebViewImpl::setDeviceScaleFactor(float scaleFactor)
 {
@@ skipping 1345 matching lines @@
     const PageScaleConstraints& constraints = m_pageScaleConstraintsSet.pageDefinedConstraints();
 
     if (!mainFrameImpl() || !mainFrameImpl()->frameView())
         return false;
 
     return mainFrameImpl()->frameView()->layoutSize().width() == m_size.width
         || (constraints.minimumScale == constraints.maximumScale && constraints.minimumScale != -1);
 }
 
 } // namespace blink