Bug 818766 - disable by default losing WebGL contexts on heap-minimize, add a pref for it - r=jgilbert

b2g/app/b2g.js

@@ -595,3 +595,7 @@ pref("memory.free_dirty_pages", true);
 // UAProfile settings
 pref("wap.UAProf.url", "");
 pref("wap.UAProf.tagname", "x-wap-profile");
+
+// b2g currently triggers heap-minimize more often than we want to lose WebGL contexts.
+// Until this is resolved, let's not lost WebGL contexts on heap-minimize. See bug 818766.
+pref("webgl.lose-context-on-heap-minimize", false);

content/canvas/src/WebGLContext.cpp

@@ -58,9 +58,18 @@ WebGLMemoryPressureObserver::Observe(nsISupports* aSubject,
                                      const char* aTopic,
                                      const PRUnichar* aSomeData)
 {
-  if (strcmp(aTopic, "memory-pressure") == 0)
-    mContext->ForceLoseContext();
-  return NS_OK;
+    if (strcmp(aTopic, "memory-pressure"))
+        return NS_OK;
+
+    bool wantToLoseContext = true;
+
+    if (!nsCRT::strcmp(aSomeData, NS_LITERAL_STRING("heap-minimize").get()))
+        wantToLoseContext = mContext->mLoseContextOnHeapMinimize;
+
+    if (wantToLoseContext)
+        mContext->ForceLoseContext();
+
+    return NS_OK;
 }
 
 
@@ -168,6 +177,7 @@ WebGLContext::WebGLContext()
     mContextRestorer = do_CreateInstance("@mozilla.org/timer;1");
     mContextStatus = ContextStable;
     mContextLostErrorSet = false;
+    mLoseContextOnHeapMinimize = false;
 
     mAlreadyGeneratedWarnings = 0;
     mAlreadyWarnedAboutFakeVertexAttrib0 = false;

content/canvas/src/WebGLContext.h

@@ -843,6 +843,7 @@ protected:
     bool mDisableExtensions;
     bool mHasRobustness;
     bool mIsMesa;
+    bool mLoseContextOnHeapMinimize;
 
     template<typename WebGLObjectType>
     void DeleteWebGLObjectsArray(nsTArray<WebGLObjectType>& array);

content/canvas/src/WebGLContextValidate.cpp

@@ -852,6 +852,7 @@ WebGLContext::InitAndValidateGL()
 
     mMinCapability = Preferences::GetBool("webgl.min_capability_mode", false);
     mDisableExtensions = Preferences::GetBool("webgl.disable-extensions", false);
+    mLoseContextOnHeapMinimize = Preferences::GetBool("webgl.lose-context-on-heap-minimize", false);
 
     mActiveTexture = 0;
     mWebGLError = LOCAL_GL_NO_ERROR;

modules/libpref/src/init/all.js

@@ -3665,6 +3665,7 @@ pref("webgl.msaa-force", false);
 pref("webgl.prefer-16bpp", false);
 pref("webgl.default-no-alpha", false);
 pref("webgl.force-layers-readback", false);
+pref("webgl.lose-context-on-heap-minimize", true);
 
 // Stagefright prefs
 pref("stagefright.force-enabled", false);