Force OMTC on when enabling multi-process tabs (bug 897502, r=ncameron).

gfx/thebes/gfxPlatform.cpp

@@ -362,17 +362,18 @@ gfxPlatform::Init()
     mozilla::gl::GLContext::StaticInit();
 #endif
 
-    bool useOffMainThreadCompositing = GetPrefLayersOffMainThreadCompositionEnabled() ||
-        Preferences::GetBool("browser.tabs.remote", false);
-    useOffMainThreadCompositing &= GetPlatform()->SupportsOffMainThreadCompositing();
+    bool useOffMainThreadCompositing = OffMainThreadCompositionRequired() ||
+                                       GetPrefLayersOffMainThreadCompositionEnabled();
 
-    if (useOffMainThreadCompositing && (XRE_GetProcessType() ==
-                                        GeckoProcessType_Default)) {
+    if (!OffMainThreadCompositionRequired()) {
+      useOffMainThreadCompositing &= GetPlatform()->SupportsOffMainThreadCompositing();
+    }
+
+    if (useOffMainThreadCompositing && (XRE_GetProcessType() == GeckoProcessType_Default)) {
         CompositorParent::StartUp();
-        if (Preferences::GetBool("layers.async-video.enabled",false)) {
+        if (Preferences::GetBool("layers.async-video.enabled", false)) {
             ImageBridgeChild::StartUp();
         }
-
     }
 
     nsresult rv;
@@ -1886,6 +1887,7 @@ static bool sLayersSupportsD3D9 = true;
 static int  sPrefLayoutFrameRate = -1;
 static bool sBufferRotationEnabled = false;
 static bool sComponentAlphaEnabled = true;
+static bool sPrefBrowserTabsRemote = false;
 
 static bool sLayersAccelerationPrefsInitialized = false;
 
@@ -1904,6 +1906,7 @@ InitLayersAccelerationPrefs()
     sPrefLayoutFrameRate = Preferences::GetInt("layout.frame_rate", -1);
     sBufferRotationEnabled = Preferences::GetBool("layers.bufferrotation.enabled", true);
     sComponentAlphaEnabled = Preferences::GetBool("layers.componentalpha.enabled", true);
+    sPrefBrowserTabsRemote = Preferences::GetBool("browser.tabs.remote", false);
 
     nsCOMPtr<nsIGfxInfo> gfxInfo = do_GetService("@mozilla.org/gfx/info;1");
     if (gfxInfo) {
@@ -1942,6 +1945,12 @@ gfxPlatform::GetPrefLayersAccelerationForceEnabled()
   return sPrefLayersAccelerationForceEnabled;
 }
 
+bool gfxPlatform::OffMainThreadCompositionRequired()
+{
+  InitLayersAccelerationPrefs();
+  return sPrefBrowserTabsRemote;
+}
+
 bool
 gfxPlatform::GetPrefLayersAccelerationDisabled()
 {

gfx/thebes/gfxPlatform.h

@@ -487,6 +487,8 @@ public:
     static bool CanUseDirect3D9();
     static int  GetPrefLayoutFrameRate();
 
+    static bool OffMainThreadCompositionRequired();
+
     /**
      * Is it possible to use buffer rotation
      */

gfx/thebes/gfxPlatformGtk.cpp

@@ -502,7 +502,8 @@ gfxPlatformGtk::GetScreenDepth() const
 bool
 gfxPlatformGtk::SupportsOffMainThreadCompositing()
 {
-#ifdef MOZ_X11
+  // Nightly builds have OMTC support by default for Electrolysis testing.
+#if defined(MOZ_X11) && !defined(NIGHTLY_BUILD)
   return (PR_GetEnv("MOZ_USE_OMTC") != nullptr) ||
          (PR_GetEnv("MOZ_OMTC_ENABLED") != nullptr);
 #else

toolkit/xre/nsAppRunner.cpp

@@ -3370,11 +3370,19 @@ XREMain::XRE_mainStartup(bool* aExitFlag)
   // (called inside gdk_display_open). This is a requirement for off main tread compositing.
   // This is done only on X11 platforms if the environment variable MOZ_USE_OMTC is set so 
   // as to avoid overhead when omtc is not used. 
+  //
+  // On nightly builds, we call this by default to enable OMTC for Electrolysis testing. On
+  // aurora, beta, and release builds, there is a small tpaint regression from enabling this
+  // call, so it sits behind an environment variable.
+  //
   // An environment variable is used instead of a pref on X11 platforms because we start having 
   // access to prefs long after the first call to XOpenDisplay which is hard to change due to 
   // interdependencies in the initialization.
+# ifndef NIGHTLY_BUILD
   if (PR_GetEnv("MOZ_USE_OMTC") ||
-      PR_GetEnv("MOZ_OMTC_ENABLED")) {
+      PR_GetEnv("MOZ_OMTC_ENABLED"))
+# endif
+  {
     XInitThreads();
   }
 #endif

widget/cocoa/nsChildView.mm

@@ -1534,8 +1534,7 @@ nsChildView::ComputeShouldAccelerate(bool aDefault)
 bool
 nsChildView::ShouldUseOffMainThreadCompositing()
 {
-  // Don't use OMTC (which requires OpenGL) for transparent windows or for
-  // popup windows.
+  // Don't use OMTC for transparent windows or for popup windows.
   if (!mView || ![[mView window] isOpaque] ||
       [[mView window] isKindOfClass:[PopupWindow class]])
     return false;