commit 8da867557a9ed03fbc89182983645be0e06af2af
Author: Allan Sandfeld Jensen <allan.jensen@digia.com>
Date:   Tue Sep 3 17:32:55 2013 +0200

    [Qt] Images scaled poorly on composited canvas
    
    https://bugs.webkit.org/show_bug.cgi?id=120632
    
    Reviewed by Jocelyn Turcotte.
    
    Explicitly set a imageInterpolationQuality on the TextureMapper, because
    InterpolationDefault may be interpreted differently by nested GraphicsContexts.
    
    * WebCoreSupport/TextureMapperLayerClientQt.cpp:
    (TextureMapperLayerClientQt::renderCompositedLayers):
    
    git-svn-id: http://svn.webkit.org/repository/webkit/trunk@154985 268f45cc-cd09-0410-ab3c-d52691b4dbfc
    
    Task-number: QTBUG-33081
    Change-Id: Iec90f53da38c4520cef2aac0519e36af74dd5a50

diff --git a/Source/WebKit/qt/WebCoreSupport/TextureMapperLayerClientQt.cpp b/Source/WebKit/qt/WebCoreSupport/TextureMapperLayerClientQt.cpp
index 4442baf..8b4748b 100644
--- a/Source/WebKit/qt/WebCoreSupport/TextureMapperLayerClientQt.cpp
+++ b/Source/WebKit/qt/WebCoreSupport/TextureMapperLayerClientQt.cpp
@@ -103,7 +103,14 @@ void TextureMapperLayerClientQt::renderCompositedLayers(GraphicsContext* context
         return;
 
     m_textureMapper->setGraphicsContext(context);
-    m_textureMapper->setImageInterpolationQuality(context->imageInterpolationQuality());
+    // GraphicsContext::imageInterpolationQuality is always InterpolationDefault here,
+    // but 'default' may be interpreted differently due to a different backend QPainter,
+    // so we need to set an explicit imageInterpolationQuality.
+    if (context->platformContext()->renderHints() & QPainter::SmoothPixmapTransform)
+        m_textureMapper->setImageInterpolationQuality(WebCore::InterpolationMedium);
+    else
+        m_textureMapper->setImageInterpolationQuality(WebCore::InterpolationNone);
+
     m_textureMapper->setTextDrawingMode(context->textDrawingMode());
     QPainter* painter = context->platformContext();
     const QTransform transform = painter->worldTransform();