Optimization suggested by Ryan:

Don't set the same OpenGL context multiple times

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%402607

src/video/SDL_sysvideo.h

@@ -126,6 +126,7 @@ struct SDL_Window
 
     int display;
     SDL_Renderer *renderer;
+    SDL_GLContext context;
 
     void *userdata;
     void *driverdata;

src/video/SDL_video.c

@@ -2566,6 +2566,12 @@ SDL_GL_MakeCurrent(SDL_WindowID windowID, SDL_GLContext context)
     if (!context) {
         window = NULL;
     }
+    if (window) {
+        if (window->context == context) {
+            return 0;
+        }
+        window->context = context;
+    }
     return _this->GL_MakeCurrent(_this, window, context);
 }