Bug 596544 - These WebGL samples are slow on Firefox, fast on Chrome - r=vladimir, a=joe

gfx/thebes/GLContextProviderGLX.cpp

@@ -98,6 +98,7 @@ GLXLibrary::EnsureInitialized()
         { (PRFuncPtr*) &xDestroyPixmap, { "glXDestroyPixmap", NULL } },
         { (PRFuncPtr*) &xGetClientString, { "glXGetClientString", NULL } },
         { (PRFuncPtr*) &xCreateContext, { "glXCreateContext", NULL } },
+        { (PRFuncPtr*) &xGetCurrentContext, { "glXGetCurrentContext", NULL } },
         { NULL, { NULL } }
     };
 
@@ -254,8 +255,19 @@ TRY_AGAIN_NO_SHARING:
 
     PRBool MakeCurrent(PRBool aForce = PR_FALSE)
     {
-        Bool succeeded = sGLXLibrary.xMakeCurrent(mDisplay, mDrawable, mContext);
-        NS_ASSERTION(succeeded, "Failed to make GL context current!");
+        PRBool succeeded = PR_TRUE;
+
+        // With the ATI FGLRX driver, glxMakeCurrent is very slow even when the context doesn't change.
+        // (This is not the case with other drivers such as NVIDIA).
+        // So avoid calling it more than necessary. Since GLX documentation says that:
+        //     "glXGetCurrentContext returns client-side information.
+        //      It does not make a round trip to the server."
+        // I assume that it's not worth using our own TLS slot here.
+        if (aForce || sGLXLibrary.xGetCurrentContext() != mContext) {
+            succeeded = sGLXLibrary.xMakeCurrent(mDisplay, mDrawable, mContext);
+            NS_ASSERTION(succeeded, "Failed to make GL context current!");
+        }
+
         return succeeded;
     }
 

gfx/thebes/GLXLibrary.h

@@ -54,6 +54,8 @@ public:
                                                        GLXDrawable,
                                                        GLXContext);
     PFNGLXMAKECURRENTPROC xMakeCurrent;
+    typedef GLXContext (GLAPIENTRY * PFNGLXGETCURRENTCONTEXT) ();
+    PFNGLXGETCURRENTCONTEXT xGetCurrentContext;
     typedef void* (GLAPIENTRY * PFNGLXGETPROCADDRESSPROC) (const char *);
     PFNGLXGETPROCADDRESSPROC xGetProcAddress;
     typedef XVisualInfo* (GLAPIENTRY * PFNGLXCHOOSEVISUALPROC) (Display*,