Translate viewport related meta tags into @viewport descriptors as suggested by the CSS Device Adap…

Source/core/page/PageScaleConstraintsSet.cpp

 /*
  * Copyright (C) 2013 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 31 matching lines @@
     , m_constraintsDirty(false)
 {
     m_finalConstraints = defaultConstraints();
 }
 
 PageScaleConstraints PageScaleConstraintsSet::defaultConstraints() const
 {
     return PageScaleConstraints(-1, defaultMinimumScale, defaultMaximumScale);
 }
 
-void PageScaleConstraintsSet::updatePageDefinedConstraints(const ViewportArguments& arguments, IntSize viewSize, int layoutFallbackWidth)
+void PageScaleConstraintsSet::updatePageDefinedConstraints(const ViewportArguments& arguments, IntSize viewSize)
 {
-    m_pageDefinedConstraints = arguments.resolve(viewSize, layoutFallbackWidth);
+    m_pageDefinedConstraints = arguments.resolve(viewSize);
 
     m_constraintsDirty = true;
 }
 
 void PageScaleConstraintsSet::setUserAgentConstraints(const PageScaleConstraints& userAgentConstraints)
 {
     m_userAgentConstraints = userAgentConstraints;
     m_constraintsDirty = true;
 }
 
@@ skipping 49 matching lines @@
     return targetDPI > 0 ? 160.0f / targetDPI : 1.0f;
 }
 
 static float getLayoutWidthForNonWideViewport(const FloatSize& deviceSize, float initialScale)
 {
     return initialScale == -1 ? deviceSize.width() : deviceSize.width() / initialScale;
 }
 
 void PageScaleConstraintsSet::adjustPageDefinedConstraintsForAndroidWebView(const ViewportArguments& arguments, IntSize viewSize, int layoutFallbackWidth, float deviceScaleFactor, bool useWideViewport, bool loadWithOverviewMode)
 {
-    float initialScale = m_pageDefinedConstraints.initialScale;
-    if (arguments.zoom == -1 && !loadWithOverviewMode) {
-        if (arguments.width == -1 || (useWideViewport && arguments.width != ViewportArguments::ValueDeviceWidth))
+    float zoom = m_pageDefinedConstraints.initialScale;
+    if (zoom < 0 && !loadWithOverviewMode) {
+        if (arguments.minWidth < 0 || useWideViewport)
             m_pageDefinedConstraints.initialScale = 1.0f;
     }
 
     float targetDensityDPIFactor = computeDeprecatedTargetDensityDPIFactor(arguments, deviceScaleFactor);
     if (m_pageDefinedConstraints.initialScale != -1)
         m_pageDefinedConstraints.initialScale *= targetDensityDPIFactor;
     m_pageDefinedConstraints.minimumScale *= targetDensityDPIFactor;
     m_pageDefinedConstraints.maximumScale *= targetDensityDPIFactor;
 
     float adjustedLayoutSizeWidth = m_pageDefinedConstraints.layoutSize.width();
-    if (useWideViewport && arguments.width == -1 && arguments.zoom != 1.0f)
+
+    if (!useWideViewport)
+        adjustedLayoutSizeWidth = getLayoutWidthForNonWideViewport(viewSize, zoom);
+
+    adjustedLayoutSizeWidth /= targetDensityDPIFactor;
+
+    // FIXME: Why this particular Android behavior?
+    //
+    // <meta name="viewport" content="initial-scale=2.0"> translates into:
+    // @viewport { zoom: 2.0; width: extend-to-zoom; } according to the spec.

[aelias_OOO_until_Jul13, 2013/08/27 16:58:09]

We've observed that classic Android WebView does not behave this way;
initial-scale didn't affect the layout width in that implementation (and some
apps have come to depend on this).  mnaganov@ recently prepared a patch to apply
this quirk more generally behind a setting:
https://codereview.chromium.org/23038013/ .

+    //
+    // But Android seems to convert the width into 'auto';
+    if (useWideViewport && arguments.maxWidth < 0 && arguments.zoom != 1.0f)
         adjustedLayoutSizeWidth = layoutFallbackWidth;
-    else {
-        if (!useWideViewport)
-            adjustedLayoutSizeWidth = getLayoutWidthForNonWideViewport(viewSize, initialScale);
-        if (!useWideViewport || arguments.width == -1 || arguments.width == ViewportArguments::ValueDeviceWidth)
-            adjustedLayoutSizeWidth /= targetDensityDPIFactor;
-    }
 
     ASSERT(m_pageDefinedConstraints.layoutSize.width() > 0);
     float adjustedLayoutSizeHeight = (adjustedLayoutSizeWidth * m_pageDefinedConstraints.layoutSize.height()) / m_pageDefinedConstraints.layoutSize.width();
+
     m_pageDefinedConstraints.layoutSize.setWidth(adjustedLayoutSizeWidth);
     m_pageDefinedConstraints.layoutSize.setHeight(adjustedLayoutSizeHeight);
 }
 
 } // namespace WebCore