WebRender preference (gfx.webrender.enable, false by default)

gfx/layers/composite/ColorLayerComposite.cpp

@@ -14,6 +14,7 @@
 #include "mozilla/layers/CompositorTypes.h"  // for DiagnosticFlags::COLOR
 #include "mozilla/layers/Effects.h"     // for Effect, EffectChain, etc
 #include "mozilla/mozalloc.h"           // for operator delete, etc
+#include "gfxPrefs.h"                   // for gfxPrefs::WebRenderEnabled
 
 namespace mozilla {
 namespace layers {
@@ -34,7 +35,7 @@ ColorLayerComposite::RenderLayer(const IntRect& aClipRect)
     // Masked or 3D layers continue through the established effect path until
     // equivalent WebRender primitives are available for those cases.
     CompositorOGL* compositorOGL = mCompositor->AsCompositorOGL();
-    if (compositorOGL &&
+    if (gfxPrefs::WebRenderEnabled() && compositorOGL &&
         !effectChain.mSecondaryEffects[EffectTypes::MASK] &&
         GetEffectiveMixBlendMode() == CompositionOp::OP_OVER &&
         transform.Is2D() && !clipRect.IsEmpty()) {

gfx/thebes/gfxPrefs.h

@@ -409,6 +409,8 @@ private:
 
   DECL_GFX_PREF(Once, "gfx.use-iosurface-textures",            UseIOSurfaceTextures, bool, false);
 
+  DECL_GFX_PREF(Live, "gfx.webrender.enabled",                WebRenderEnabled, bool, false);
+
   // These times should be in milliseconds
   DECL_GFX_PREF(Once, "gfx.touch.resample.delay-threshold",    TouchResampleVsyncDelayThreshold, int32_t, 20);
   DECL_GFX_PREF(Once, "gfx.touch.resample.max-predict",        TouchResampleMaxPredict, int32_t, 8);

modules/libpref/init/all.js

@@ -727,6 +727,9 @@ pref("layout.scroll.root-frame-containers", false);
 pref("gfx.layerscope.enabled", false);
 pref("gfx.layerscope.port", 23456);
 
+// Enable the incremental C WebRender path for supported compositor primitives.
+pref("gfx.webrender.enabled", false);
+
 // Log severe performance warnings to the error console and profiles.
 // This should be use to quickly find which slow paths are used by test cases.
 pref("gfx.perf-warnings.enabled", false);