From 86af4e1c9946cf816bc33efadf6492a99bec410c Mon Sep 17 00:00:00 2001
From: Chris Lord <chrislord.net@gmail.com>
Date: Wed, 21 Nov 2012 19:16:53 +0000
Subject: [PATCH] Bug 783368 - Add a pref to control low precision tile
 rendering. r=bgirard

Add pref 'layers.low-precision-buffer', enabled on mobile/android.
---
 gfx/layers/basic/BasicTiledThebesLayer.cpp |  3 ++-
 gfx/thebes/gfxPlatform.cpp                 | 16 ++++++++++++++++
 gfx/thebes/gfxPlatform.h                   |  4 ++++
 mobile/android/app/mobile.js               |  1 +
 4 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/gfx/layers/basic/BasicTiledThebesLayer.cpp b/gfx/layers/basic/BasicTiledThebesLayer.cpp
index f172f7bbeedf..06177540bb2b 100644
--- a/gfx/layers/basic/BasicTiledThebesLayer.cpp
+++ b/gfx/layers/basic/BasicTiledThebesLayer.cpp
@@ -591,7 +591,8 @@ BasicTiledThebesLayer::PaintThebes(gfxContext* aContext,
   // If we have a critical display-port defined, render the full display-port
   // progressively in the low-precision tiled buffer.
   bool updatedLowPrecision = false;
-  if (!criticalDisplayPort.IsEmpty() &&
+  if (gfxPlatform::UseLowPrecisionBuffer() &&
+      !criticalDisplayPort.IsEmpty() &&
       !nsIntRegion(layerDisplayPort).Contains(mVisibleRegion)) {
     nsIntRegion oldValidRegion = mLowPrecisionTiledBuffer.GetValidRegion();
     oldValidRegion.And(oldValidRegion, mVisibleRegion);
diff --git a/gfx/thebes/gfxPlatform.cpp b/gfx/thebes/gfxPlatform.cpp
index bb4a89b51189..c9c14235b665 100644
--- a/gfx/thebes/gfxPlatform.cpp
+++ b/gfx/thebes/gfxPlatform.cpp
@@ -1246,6 +1246,22 @@ gfxPlatform::UseProgressiveTilePainting()
     return sUseProgressiveTilePainting;
 }
 
+bool
+gfxPlatform::UseLowPrecisionBuffer()
+{
+    static bool sUseLowPrecisionBuffer;
+    static bool sUseLowPrecisionBufferPrefCached = false;
+
+    if (!sUseLowPrecisionBufferPrefCached) {
+        sUseLowPrecisionBufferPrefCached = true;
+        mozilla::Preferences::AddBoolVarCache(&sUseLowPrecisionBuffer,
+                                              "layers.low-precision-buffer",
+                                              false);
+    }
+
+    return sUseLowPrecisionBuffer;
+}
+
 bool
 gfxPlatform::UseReusableTileStore()
 {
diff --git a/gfx/thebes/gfxPlatform.h b/gfx/thebes/gfxPlatform.h
index f35748b84772..a5ac4350f2a3 100644
--- a/gfx/thebes/gfxPlatform.h
+++ b/gfx/thebes/gfxPlatform.h
@@ -405,6 +405,10 @@ public:
     // Break large OMTC tiled thebes layer painting into small paints.
     static bool UseProgressiveTilePainting();
 
+    // When a critical display-port is set, render the visible area outside of
+    // it into a buffer at a lower precision. Requires tiled buffers.
+    static bool UseLowPrecisionBuffer();
+
     // Retain some invalid tiles when the valid region of a layer changes and
     // excludes previously valid tiles.
     static bool UseReusableTileStore();
diff --git a/mobile/android/app/mobile.js b/mobile/android/app/mobile.js
index 9dc64260b96c..33af782c1eea 100644
--- a/mobile/android/app/mobile.js
+++ b/mobile/android/app/mobile.js
@@ -523,6 +523,7 @@ pref("layers.acceleration.disabled", false);
 pref("layers.offmainthreadcomposition.enabled", true);
 pref("layers.async-video.enabled", true);
 pref("layers.progressive-paint", true);
+pref("layers.low-precision-buffer", true);
 
 pref("notification.feature.enabled", true);