Bug 747274 - Add a pref (default to true on Android) to forcibly use nearest pixel filtering for background drawing. r=jrmuizel,ajuma a=blassey

layout/base/nsLayoutUtils.cpp

@@ -168,6 +168,20 @@ nsLayoutUtils::Are3DTransformsEnabled()
   return s3DTransformsEnabled;
 }
 
+bool
+nsLayoutUtils::UseBackgroundNearestFiltering()
+{
+  static bool sUseBackgroundNearestFilteringEnabled;
+  static bool sUseBackgroundNearestFilteringPrefInitialised = false;
+
+  if (!sUseBackgroundNearestFilteringPrefInitialised) {
+    sUseBackgroundNearestFilteringPrefInitialised = true;
+    sUseBackgroundNearestFilteringEnabled = mozilla::Preferences::GetBool("gfx.filter.nearest.force-enabled", false);
+  }
+
+  return sUseBackgroundNearestFilteringEnabled;
+}
+
 void
 nsLayoutUtils::UnionChildOverflow(nsIFrame* aFrame,
                                   nsOverflowAreas& aOverflowAreas)
@@ -3734,6 +3748,11 @@ nsLayoutUtils::DrawBackgroundImage(nsRenderingContext* aRenderingContext,
                                    PRUint32            aImageFlags)
 {
   SAMPLE_LABEL("layout", "nsLayoutUtils::DrawBackgroundImage");
+
+  if (UseBackgroundNearestFiltering()) {
+    aGraphicsFilter = gfxPattern::FILTER_NEAREST;
+  }
+
   return DrawImageInternal(aRenderingContext, aImage, aGraphicsFilter,
                            aDest, aFill, aAnchor, aDirty,
                            aImageSize, aImageFlags);

layout/base/nsLayoutUtils.h

@@ -1496,6 +1496,12 @@ public:
    */
   static bool Are3DTransformsEnabled();
 
+  /**
+   * Checks if we should forcibly use nearest pixel filtering for the
+   * background.
+   */
+  static bool UseBackgroundNearestFiltering();
+
   /**
    * Unions the overflow areas of all non-popup children of aFrame with
    * aOverflowAreas.

modules/libpref/src/init/all.js

@@ -212,6 +212,12 @@ pref("gfx.downloadable_fonts.enabled", true);
 pref("gfx.downloadable_fonts.fallback_delay", 3000);
 pref("gfx.downloadable_fonts.sanitize", true);
 
+#ifdef ANDROID
+pref("gfx.filter.nearest.force-enabled", true);
+#else
+pref("gfx.filter.nearest.force-enabled", false);
+#endif
+
 // whether to always search all font cmaps during system font fallback
 pref("gfx.font_rendering.fallback.always_use_cmaps", false);