XCB/XVideo: reject hardware surfaces for the time being

The core cannot blend subpictures to hardware surfaces. In principles,
blending could be performed post chroma conversion, but this is not
supported by the video output wrapper so far.

modules/video_output/xcb/xvideo.c

@@ -374,6 +374,14 @@ static int Open (vlc_object_t *obj)
 
     if (!var_InheritBool (obj, "overlay"))
         return VLC_EGENERIC;
+    else
+    {   /* NOTE: Reject hardware surface formats. Blending would break. */
+        const vlc_chroma_description_t *chroma =
+            vlc_fourcc_GetChromaDescription(vd->source.i_chroma);
+        if (chroma != NULL && chroma->plane_count == 0)
+            return VLC_EGENERIC;
+    }
+
     p_sys = malloc (sizeof (*p_sys));
     if (p_sys == NULL)
         return VLC_ENOMEM;