Bug 486918 - Create and obey a high-quality downscaling pref, and turn it off on OS X and mobile. r=jlebar

b2g/app/b2g.js

@@ -27,6 +27,7 @@ pref("browser.cache.memory.capacity", 1024); // kilobytes
 
 /* image cache prefs */
 pref("image.cache.size", 1048576); // bytes
+pref("image.high_quality_downscaling.enabled", false);
 
 /* offline cache prefs */
 pref("browser.offline-apps.notify", false);

image/src/RasterImage.cpp

@@ -109,6 +109,9 @@ static PRLogModuleInfo *gCompressedImageAccountingLog = PR_NewLogModule ("Compre
 // makes us slower to start up.
 static uint32_t gDecodeBytesAtATime = 0;
 static uint32_t gMaxMSBeforeYield = 0;
+static bool gHQDownscaling = false;
+// This is interpreted as a floating-point value / 1000
+static uint32_t gHQDownscalingMinFactor = 1000;
 
 static void
 InitPrefCaches()
@@ -117,6 +120,10 @@ InitPrefCaches()
                                "image.mem.decode_bytes_at_a_time", 200000);
   Preferences::AddUintVarCache(&gMaxMSBeforeYield,
                                "image.mem.max_ms_before_yield", 400);
+  Preferences::AddBoolVarCache(&gHQDownscaling,
+                               "image.high_quality_downscaling.enabled", false);
+  Preferences::AddUintVarCache(&gHQDownscalingMinFactor,
+                               "image.high_quality_downscaling.min_factor", 1000);
 }
 
 /* We define our own error checking macros here for 2 reasons:
@@ -189,9 +196,6 @@ namespace mozilla {
 namespace image {
 
 /* static */ StaticRefPtr<RasterImage::DecodeWorker> RasterImage::DecodeWorker::sSingleton;
-
-#define PRE_DOWNSCALE_MIN_FACTOR 0.9
-
 /* static */ nsRefPtr<RasterImage::ScaleWorker> RasterImage::ScaleWorker::sSingleton;
 /* static */ nsRefPtr<RasterImage::DrawWorker> RasterImage::DrawWorker::sSingleton;
 static nsCOMPtr<nsIThread> sScaleWorkerThread = nullptr;
@@ -2793,14 +2797,15 @@ RasterImage::CanScale(gfxPattern::GraphicsFilter aFilter,
 {
 // The high-quality scaler requires Skia.
 #ifdef MOZ_ENABLE_SKIA
-  return (aFilter == gfxPattern::FILTER_GOOD) &&
-          !mAnim && mDecoded &&
-          (aScale.width <= 1.0 && aScale.height <= 1.0) &&
-          (aScale.width < PRE_DOWNSCALE_MIN_FACTOR ||
-           aScale.height < PRE_DOWNSCALE_MIN_FACTOR);
-#else
-  return false;
+  if (gHQDownscaling && aFilter == gfxPattern::FILTER_GOOD &&
+      !mAnim && mDecoded &&
+      (aScale.width <= 1.0 && aScale.height <= 1.0)) {
+    gfxFloat factor = gHQDownscalingMinFactor / 1000.0;
+    return (aScale.width < factor || aScale.height < factor);
+  }
 #endif
+
+  return false;
 }
 
 void

layout/tools/reftest/bootstrap.js

@@ -27,6 +27,8 @@ function setDefaultPrefs() {
     // Disable addon updates and prefetching so we don't leak them
     branch.setBoolPref("extensions.update.enabled", false);
     branch.setBoolPref("extensions.getAddons.cache.enabled", false);
+    // Disable high-quality downscaling, since it makes reftests more difficult.
+    branch.setBoolPref("image.high_quality_downscaling.enabled", false);
 }
 
 var windowListener = {

layout/tools/reftest/reftest-cmdline.js

@@ -91,6 +91,8 @@ RefTestCmdLineHandler.prototype =
     // Disable addon updates and prefetching so we don't leak them
     branch.setBoolPref("extensions.update.enabled", false);
     branch.setBoolPref("extensions.getAddons.cache.enabled", false);
+    // Disable high-quality downscaling, since it makes reftests more difficult.
+    branch.setBoolPref("image.high_quality_downscaling.enabled", false);
 
     var wwatch = Components.classes["@mozilla.org/embedcomp/window-watcher;1"]
                            .getService(nsIWindowWatcher);

mobile/android/app/mobile.js

@@ -60,6 +60,7 @@ pref("browser.cache.memory.capacity", 1024); // kilobytes
 
 /* image cache prefs */
 pref("image.cache.size", 1048576); // bytes
+pref("image.high_quality_downscaling.enabled", false);
 
 /* offline cache prefs */
 pref("browser.offline-apps.notify", true);

modules/libpref/src/init/all.js

@@ -3520,7 +3520,7 @@ pref("zoom.minPercent", 30);
 pref("zoom.maxPercent", 300);
 pref("toolkit.zoomManager.zoomValues", ".3,.5,.67,.8,.9,1,1.1,1.2,1.33,1.5,1.7,2,2.4,3");
 
-// Image cache prefs
+// Image-related prefs
 // The maximum size, in bytes, of the decoded images we cache
 pref("image.cache.size", 5242880);
 // A weight, from 0-1000, to place on time when comparing to size.
@@ -3530,6 +3530,18 @@ pref("image.cache.timeweight", 500);
 // The default Accept header sent for images loaded over HTTP(S)
 pref("image.http.accept", "image/png,image/*;q=0.8,*/*;q=0.5");
 
+// Whether we do high-quality image downscaling. OS X natively supports
+// high-quality image scaling.
+#ifdef XP_MACOSX
+pref("image.high_quality_downscaling.enabled", false);
+#else
+pref("image.high_quality_downscaling.enabled", true);
+#endif
+
+// The minimum percent downscaling we'll use high-quality downscaling on,
+// interpreted as a floating-point number / 1000.
+pref("image.high_quality_downscaling.min_factor", 1000);
+
 //
 // Image memory management prefs
 //