[Blink] Don't center images in Android WebViews

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

Index: third_party/WebKit/Source/core/html/ImageDocument.cpp
diff --git a/third_party/WebKit/Source/core/html/ImageDocument.cpp b/third_party/WebKit/Source/core/html/ImageDocument.cpp
index 5a716aa9331096f846fcd571083c1446490fd60f..8db35fecc367c43837c7df7c7a33a20a8ce5ff5e 100644
--- a/third_party/WebKit/Source/core/html/ImageDocument.cpp
+++ b/third_party/WebKit/Source/core/html/ImageDocument.cpp
@@ -48,6 +48,7 @@
 #include "core/loader/FrameLoader.h"
 #include "core/loader/FrameLoaderClient.h"
 #include "core/loader/resource/ImageResource.h"
+#include "core/page/Page.h"
 #include "platform/HostWindow.h"
 #include "wtf/text/StringBuilder.h"
 #include <limits>
@@ -235,7 +236,7 @@ void ImageDocument::createDocumentStructure() {
 
   HTMLBodyElement* body = HTMLBodyElement::create(*this);
 
-  if (shouldShrinkToFit()) {
+  if (shouldCenterImage()) {
     // Display the image prominently centered in the frame.
     body->setAttribute(styleAttr, "margin: 0px; background: #0e0e0e;");
 
@@ -292,6 +293,12 @@ void ImageDocument::createDocumentStructure() {
   rootElement->appendChild(body);
 }
 
+bool ImageDocument::shouldCenterImage() const {
+  bool isAndroidWebView =
+      page() ? page()->settings().getWideViewportQuirkEnabled() : false;
+  return shouldShrinkToFit() && !isAndroidWebView;
+}
+
 float ImageDocument::scale() const {
   DCHECK_EQ(m_shrinkToFitMode, Desktop);
   if (!m_imageElement || m_imageElement->document() != this)
@@ -379,31 +386,36 @@ void ImageDocument::updateImageStyle() {
   imageStyle.append("-webkit-user-select: none;");
 
   if (shouldShrinkToFit()) {
-    if (m_shrinkToFitMode == Viewport)
+    if (shouldCenterImage() && m_shrinkToFitMode == Viewport) {
+      // The image occupies the full width of its parent <div>.
       imageStyle.append("max-width: 100%;");
+    }
 
-    // Once the image has fully loaded, it is displayed atop a checkerboard to
-    // show transparency more faithfully.  The pattern is generated via CSS.
     if (m_imageIsLoaded) {
       int newCheckerSize = kBaseCheckerSize;
       MouseCursorMode newCursorMode = Default;
 
+      // Images are displayed atop a checkerboard to show transparency more
+      // faithfully.  The pattern is generated via CSS.
       if (m_shrinkToFitMode == Viewport) {
-        double scale;
-
-        if (hasFinishedParsing()) {
-          // To ensure the checker pattern is visible for large images, the
-          // checker size is dynamically adjusted to account for how much the
-          // page is currently being scaled.
-          scale = frame()->host()->visualViewport().scale();
-        } else {
-          // The checker pattern is initialized based on how large the image is
-          // relative to the viewport.
-          int viewportWidth = frame()->host()->visualViewport().size().width();
-          scale = viewportWidth / static_cast<double>(calculateDivWidth());
+        if (shouldCenterImage()) {
+          double scale;
+
+          if (hasFinishedParsing()) {
+            // To ensure the checker pattern is visible for large images, the
+            // checker size is dynamically adjusted to account for how much the
+            // page is currently being scaled.
+            scale = frame()->host()->visualViewport().scale();
+          } else {
+            // The checker pattern is initialized based on how large the image
+            // is relative to the viewport.
+            int viewportWidth =
+                frame()->host()->visualViewport().size().width();
+            scale = viewportWidth / static_cast<double>(calculateDivWidth());
+          }
+
+          newCheckerSize = std::round(std::max(1.0, newCheckerSize / scale));
         }
-
-        newCheckerSize = std::round(std::max(1.0, newCheckerSize / scale));
       } else {
         // In desktop mode, the user can click on the image to zoom in or out.
         DCHECK_EQ(m_shrinkToFitMode, Desktop);
@@ -423,29 +435,33 @@ void ImageDocument::updateImageStyle() {
       m_styleCheckerSize = newCheckerSize;
       m_styleMouseCursorMode = newCursorMode;
 
-      imageStyle.append("background-position: 0px 0px, ");
-      imageStyle.append(AtomicString::number(m_styleCheckerSize));
-      imageStyle.append("px ");
-      imageStyle.append(AtomicString::number(m_styleCheckerSize));
-      imageStyle.append("px;");
-
-      int tileSize = m_styleCheckerSize * 2;
-      imageStyle.append("background-size: ");
-      imageStyle.append(AtomicString::number(tileSize));
-      imageStyle.append("px ");
-      imageStyle.append(AtomicString::number(tileSize));
-      imageStyle.append("px;");
-
-      // Generating the checkerboard pattern this way is not exactly cheap.
-      // If rasterization performance becomes an issue, we could look at using
-      // a cheaper shader (e.g. pre-generate a scaled tile + base64-encode +
-      // inline dataURI => single bitmap shader).
-      imageStyle.append(
-          "background-image:"
-          "linear-gradient(45deg, #eee 25%, transparent 25%, transparent 75%, "
-          "#eee 75%, #eee 100%),"
-          "linear-gradient(45deg, #eee 25%, white 25%, white 75%, "
-          "#eee 75%, #eee 100%);");
+      // Generate the new image style string.
+      if (shouldCenterImage()) {
+        imageStyle.append("background-position: 0px 0px, ");
+        imageStyle.append(AtomicString::number(m_styleCheckerSize));
+        imageStyle.append("px ");
+        imageStyle.append(AtomicString::number(m_styleCheckerSize));
+        imageStyle.append("px;");
+
+        int tileSize = m_styleCheckerSize * 2;
+        imageStyle.append("background-size: ");
+        imageStyle.append(AtomicString::number(tileSize));
+        imageStyle.append("px ");
+        imageStyle.append(AtomicString::number(tileSize));
+        imageStyle.append("px;");
+
+        // Generating the checkerboard pattern this way is not exactly cheap.
+        // If rasterization performance becomes an issue, we could look at using
+        // a cheaper shader (e.g. pre-generate a scaled tile + base64-encode +
+        // inline dataURI => single bitmap shader).
+        imageStyle.append(
+            "background-image:"
+            "linear-gradient(45deg, #eee 25%, transparent 25%, transparent "
+            "75%, "
+            "#eee 75%, #eee 100%),"
+            "linear-gradient(45deg, #eee 25%, white 25%, white 75%, "
+            "#eee 75%, #eee 100%);");
+      }
 
       if (m_shrinkToFitMode == Desktop) {
         if (m_styleMouseCursorMode == ZoomIn)
@@ -527,20 +543,32 @@ void ImageDocument::windowSizeChanged() {
     return;
 
   if (m_shrinkToFitMode == Viewport) {
-    LayoutSize imageSize = cachedImageSize(m_imageElement);
-    int divWidth = calculateDivWidth();
-    m_divElement->setInlineStyleProperty(CSSPropertyWidth, divWidth,
-                                         CSSPrimitiveValue::UnitType::Pixels);
-
-    // Explicitly set the height of the <div> containing the <img> so that it
-    // can display the full image without shrinking it, allowing a full-width
-    // reading mode for normal-width-huge-height images.
-    float viewportAspectRatio =
-        frame()->host()->visualViewport().size().aspectRatio();
-    int divHeight = std::max(imageSize.height().toInt(),
-                             static_cast<int>(divWidth / viewportAspectRatio));
-    m_divElement->setInlineStyleProperty(CSSPropertyHeight, divHeight,
-                                         CSSPrimitiveValue::UnitType::Pixels);
+    if (shouldCenterImage()) {
+      // Set the size of the <div> containing the <img>.  The latter is set
+      // to occupy 100% of the <div>'s width in updateImageStyle().
+      LayoutSize imageSize = cachedImageSize(m_imageElement);
+      int divWidth = calculateDivWidth();
+      m_divElement->setInlineStyleProperty(CSSPropertyWidth, divWidth,
+                                           CSSPrimitiveValue::UnitType::Pixels);
+
+      // Explicitly set the height of the <div> containing the <img> so that it
+      // can display the full image without shrinking it, allowing a full-width
+      // reading mode for normal-width-huge-height images.
+      float viewportAspectRatio =
+          frame()->host()->visualViewport().size().aspectRatio();
+      int divHeight =
+          std::max(imageSize.height().toInt(),
+                   static_cast<int>(divWidth / viewportAspectRatio));
+      m_divElement->setInlineStyleProperty(CSSPropertyHeight, divHeight,
+                                           CSSPrimitiveValue::UnitType::Pixels);
+    } else {
+      // Set the max width of the <img> to prevent it from becoming too large.
+      // See calculateDivWidth() for details.
+      int viewportWidth = frame()->host()->visualViewport().size().width();
+      m_imageElement->setInlineStyleProperty(

[aelias_OOO_until_Jul13, 2017/01/19 00:23:49]

Could you try instead returning false from ImageDocument::shouldShrinkToFit() if
page()->settings().getForceZeroLayoutHeight() is true?  I believe that should
avoid the problem in the WRAP_CONTENT WebView case while still allowing a
scale-down behavior in the MATCH_PARENT WebView case, without needing to
introduce a WebView-specific scaling path like this one.

+          CSSPropertyMaxWidth, viewportWidth * 10,
+          CSSPrimitiveValue::UnitType::Pixels);
+    }
     return;
   }