Bug 1438551 - Add a pref for enabling tiles when we are using skia with parallel painting. r=nical

MozReview-Commit-ID: JVIFr2wUWHD

--HG--
extra : rebase_source : 67cf74011993a971d66d9a7350171f0190ec08cd

gfx/thebes/gfxPlatform.cpp

@@ -2730,7 +2730,14 @@ gfxPlatform::UsesOffMainThreadCompositing()
 bool
 gfxPlatform::UsesTiling() const
 {
-  return gfxPrefs::LayersTilesEnabled();
+  bool isSkiaPOMTP = XRE_IsContentProcess() &&
+      GetDefaultContentBackend() == BackendType::SKIA &&
+      gfxVars::UseOMTP() &&
+      (gfxPrefs::LayersOMTPPaintWorkers() == -1 ||
+      gfxPrefs::LayersOMTPPaintWorkers() > 1);
+
+  return gfxPrefs::LayersTilesEnabled() ||
+    (gfxPrefs::LayersTilesEnabledIfSkiaPOMTP() && isSkiaPOMTP);
 }
 
 /***

gfx/thebes/gfxPlatform.h

@@ -300,7 +300,7 @@ public:
     // Get the default content backend that will be used with the default
     // compositor. If the compositor is known when calling this function,
     // GetContentBackendFor() should be called instead.
-    mozilla::gfx::BackendType GetDefaultContentBackend() {
+    mozilla::gfx::BackendType GetDefaultContentBackend() const {
       return mContentBackend;
     }
 

gfx/thebes/gfxPrefs.h

@@ -589,6 +589,7 @@ private:
   DECL_GFX_PREF(Live, "layers.effect.grayscale",               LayersEffectGrayscale, bool, false);
   DECL_GFX_PREF(Live, "layers.effect.invert",                  LayersEffectInvert, bool, false);
   DECL_GFX_PREF(Once, "layers.enable-tiles",                   LayersTilesEnabled, bool, false);
+  DECL_GFX_PREF(Once, "layers.enable-tiles-if-skia-pomtp",     LayersTilesEnabledIfSkiaPOMTP, bool, false);
   DECL_GFX_PREF(Live, "layers.flash-borders",                  FlashLayerBorders, bool, false);
   DECL_GFX_PREF(Once, "layers.force-shmem-tiles",              ForceShmemTiles, bool, false);
   DECL_GFX_PREF(Once, "layers.gpu-process.allow-software",     GPUProcessAllowSoftware, bool, false);

modules/libpref/init/all.js

@@ -5861,6 +5861,7 @@ pref("layers.omtp.paint-workers", -1);
 #else
 pref("layers.omtp.paint-workers", 1);
 #endif
+pref("layers.enable-tiles-if-skia-pomtp", false);
 pref("layers.omtp.release-capture-on-main-thread", false);
 pref("layers.omtp.dump-capture", false);