SDL: set a hint to not bypass the window compositor

Without that, window effects in KWin get suspended as soon as any
qemu-sdl window becomes visible. While the SDL default makes sense
for games, it's not really suitable for QEMU.
Signed-off-by: NSebastian Krzyszkowiak <dos@dosowisko.net>
Message-id: 20181024143748.4425-1-dos@dosowisko.net
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

ui/sdl2.c

@@ -786,6 +786,9 @@ static void sdl2_display_init(DisplayState *ds, DisplayOptions *o)
                 SDL_GetError());
         exit(1);
     }
+#ifdef SDL_HINT_VIDEO_X11_NET_WM_BYPASS_COMPOSITOR /* only available since SDL 2.0.8 */
+    SDL_SetHint(SDL_HINT_VIDEO_X11_NET_WM_BYPASS_COMPOSITOR, "0");
+#endif
     SDL_SetHint(SDL_HINT_GRAB_KEYBOARD, "1");
     memset(&info, 0, sizeof(info));
     SDL_VERSION(&info.version);