Fixed issue where the context couldn't be unbound after the window is shown because the current context was already marked as NULL. (Thanks to John McDonald for tracking that down!)

src/video/SDL_video.c

@@ -107,11 +107,6 @@ static SDL_VideoDevice *_this = NULL;
         return retval; \
     }
 
-#define INVALIDATE_GLCONTEXT() \
-    _this->current_glwin = NULL; \
-    _this->current_glctx = NULL;
-
-
 /* Support for framebuffer emulation using an accelerated renderer */
 
 #define SDL_WINDOWTEXTUREDATA   "_SDL_WindowTextureData"
@@ -1865,14 +1860,12 @@ SDL_GetWindowGrab(SDL_Window * window)
 void
 SDL_OnWindowShown(SDL_Window * window)
 {
-    INVALIDATE_GLCONTEXT();
     SDL_OnWindowRestored(window);
 }
 
 void
 SDL_OnWindowHidden(SDL_Window * window)
 {
-    INVALIDATE_GLCONTEXT();
     SDL_UpdateFullscreenMode(window, SDL_FALSE);
 }
 
@@ -1897,6 +1890,13 @@ SDL_OnWindowRestored(SDL_Window * window)
     if (FULLSCREEN_VISIBLE(window)) {
         SDL_UpdateFullscreenMode(window, SDL_TRUE);
     }
+
+    /* This needs to be done on iOS to rebind the nscontext to the view,
+       and (hopefully) doesn't hurt on other systems.
+    */
+    if (window == _this->current_glwin) {
+        _this->GL_MakeCurrent(_this, _this->current_glwin, _this->current_glctx);
+    }
 }
 
 void