Displays are now referenced by instance ID instead of index

test/testgles2_sdf.c

@@ -602,7 +602,7 @@ int main(int argc, char *argv[])
         SDL_GL_SetSwapInterval(0);
     }
 
-    SDL_GetCurrentDisplayMode(0, &mode);
+    SDL_GetCurrentDisplayMode(SDL_GetPrimaryDisplay(), &mode);
     SDL_Log("Screen bpp: %d\n", SDL_BITSPERPIXEL(mode.format));
     SDL_Log("\n");
     SDL_Log("Vendor     : %s\n", ctx.glGetString(GL_VENDOR));