xwayland: add workaround for drivers that don't support impicit sync

Without either implicit or explicit synchronization, the result of rendering is
pretty much undefined, and many glitches can appear. This still doesn't synchronize
buffer release, but it works around most glitches until explicit sync is supported.

Signed-off-by: Xaver Hugl <xaver.hugl@kde.org>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/967>

hw/xwayland/xwayland-present.c

@@ -695,7 +695,10 @@ xwl_present_check_flip(RRCrtcPtr crtc,
     if (xwl_window->xwl_screen->glamor &&
         !xwl_glamor_check_flip(present_window, pixmap))
         return FALSE;
-#endif
+
+    if (!xwl_glamor_supports_implicit_sync(xwl_window->xwl_screen))
+        return FALSE;
+#endif /* XWL_HAS_GLAMOR */
 
     /* Can't flip if the window pixmap doesn't match the xwl_window parent
      * window's, e.g. because a client redirected this window or one of its

hw/xwayland/xwayland-window-buffers.c

@@ -32,6 +32,9 @@
 #include "xwayland-pixmap.h"
 #include "xwayland-screen.h"
 #include "xwayland-window-buffers.h"
+#ifdef XWL_HAS_GLAMOR
+#include "glamor.h"
+#endif
 
 #define BUFFER_TIMEOUT 1 * 1000 /* ms */
 
@@ -384,6 +387,12 @@ xwl_window_swap_pixmap(struct xwl_window *xwl_window)
 
     /* Hold a reference on the buffer until it's released by the compositor */
     xwl_window_buffer->refcnt++;
+
+#ifdef XWL_HAS_GLAMOR
+    if (!xwl_glamor_supports_implicit_sync(xwl_screen)) {
+        glamor_finish(xwl_screen->screen);
+    }
+#endif /* XWL_HAS_GLAMOR */
     xwl_pixmap_set_buffer_release_cb(xwl_window_buffer->pixmap,
                                      xwl_window_buffer_release_callback,
                                      xwl_window_buffer);