Bug 771219 - Added a pref for progressive painting. r=ajuma

gfx/layers/basic/BasicTiledThebesLayer.cpp

@@ -227,9 +227,7 @@ BasicTiledThebesLayer::PaintThebes(gfxContext* aContext,
   if (regionToPaint.IsEmpty())
     return;
 
-  bool useProgressivePaint = true;
-
-  if (useProgressivePaint) {
+  if (gfxPlatform::UseProgressiveTilePainting()) {
     nsIntRegionRectIterator it(regionToPaint);
     const nsIntRect* rect = it.Next();
     if (!rect)

gfx/thebes/gfxPlatform.cpp

@@ -1080,6 +1080,22 @@ gfxPlatform::AppendPrefLang(eFontPrefLang aPrefLangs[], PRUint32& aLen, eFontPre
     }
 }
 
+bool
+gfxPlatform::UseProgressiveTilePainting()
+{
+  static bool sUseProgressiveTilePainting;
+  static bool sUseProgressiveTilePaintingPrefCached = false;
+
+  if (!sUseProgressiveTilePaintingPrefCached) {
+    sUseProgressiveTilePaintingPrefCached = true;
+    mozilla::Preferences::AddBoolVarCache(&sUseProgressiveTilePainting,
+                                          "layers.progressive-paint",
+                                          true);
+  }
+
+  return sUseProgressiveTilePainting;
+}
+
 bool
 gfxPlatform::UseAzureContentDrawing()
 {
@@ -1088,7 +1104,7 @@ gfxPlatform::UseAzureContentDrawing()
 
   if (!sAzureContentDrawingPrefCached) {
     sAzureContentDrawingPrefCached = true;
-    mozilla::Preferences::AddBoolVarCache(&sAzureContentDrawingEnabled, 
+    mozilla::Preferences::AddBoolVarCache(&sAzureContentDrawingEnabled,
                                           "gfx.content.azure.enabled");
   }
 

gfx/thebes/gfxPlatform.h

@@ -368,6 +368,9 @@ public:
         // platform-specific override, by default do nothing
     }
 
+    // Break large OMTC tiled thebes layer painting into small paints.
+    static bool UseProgressiveTilePainting();
+
     // helper method to indicate if we want to use Azure content drawing
     static bool UseAzureContentDrawing();