xwayland/present: Handle clearing damage after flip in xwl_present_execute

Due to DamageReportNonEmpty, damage_report doesn't get called if the
damage region was already non-empty before the flip. In which case it
didn't get called before the first draw after the flip either.

Closes: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1627
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1314>

hw/xwayland/xwayland-present.c

@@ -35,6 +35,7 @@
 #include "xwayland-screen.h"
 #include "xwayland-shm.h"
 #include "xwayland-window.h"
+#include "xwayland-window-buffers.h"
 #include "xwayland-pixmap.h"
 
 #include "tearing-control-v1-client-protocol.h"
@@ -833,7 +834,6 @@ xwl_present_flip(present_vblank_ptr vblank, RegionPtr damage)
     }
 
     wl_display_flush(xwl_window->xwl_screen->display);
-    xwl_window->present_flipped = TRUE;
     return TRUE;
 }
 
@@ -890,6 +890,8 @@ xwl_present_execute(present_vblank_ptr vblank, uint64_t ust, uint64_t crtc_msc)
 
             if (xwl_present_flip(vblank, damage)) {
                 WindowPtr toplvl_window = xwl_present_toplvl_pixmap_window(vblank->window);
+                struct xwl_window *xwl_window = xwl_window_from_window(window);
+                struct xwl_screen *xwl_screen = xwl_window->xwl_screen;
                 PixmapPtr old_pixmap = screen->GetWindowPixmap(window);
 
                 /* Replace window pixmap with flip pixmap */
@@ -906,10 +908,19 @@ xwl_present_execute(present_vblank_ptr vblank, uint64_t ust, uint64_t crtc_msc)
                 vblank->pixmap->refcnt++;
                 dixDestroyPixmap(old_pixmap, old_pixmap->drawable.id);
 
-                /* Report damage */
+                /* Report damage, let damage_report ignore it though */
+                xwl_screen->ignore_damage = TRUE;
                 DamageDamageRegion(&vblank->window->drawable, damage);
+                xwl_screen->ignore_damage = FALSE;
                 RegionDestroy(damage);
 
+                /* Clear damage region, to ensure damage_report is called before
+                 * any drawing to the window
+                 */
+                xwl_window_buffer_add_damage_region(xwl_window);
+                RegionEmpty(xwl_window_get_damage_region(xwl_window));
+                xorg_list_del(&xwl_window->link_damage);
+
                 /* Put pending flip at the flip queue head */
                 xorg_list_add(&vblank->event_queue, &xwl_present_window->flip_queue);
 

hw/xwayland/xwayland-screen.h

@@ -90,6 +90,7 @@ struct xwl_screen {
     struct xorg_list seat_list;
     struct xorg_list damage_window_list;
     struct xorg_list window_list;
+    Bool ignore_damage;
 
     int wayland_fd;
     struct wl_display *display;

hw/xwayland/xwayland-window.c

@@ -194,17 +194,8 @@ damage_report(DamagePtr pDamage, RegionPtr pRegion, void *data)
         return;
 
     xwl_screen = xwl_window->xwl_screen;
-
+    if (xwl_screen->ignore_damage)
-    if (xwl_window->present_flipped) {
-        /* This damage is from a Present flip, which already committed a new
-         * buffer for the surface, so we don't need to do anything in response
-         */
-        xwl_window_buffer_add_damage_region(xwl_window);
-        RegionEmpty(DamageRegion(pDamage));
-        xorg_list_del(&xwl_window->link_damage);
-        xwl_window->present_flipped = FALSE;
         return;
-    }
 
     if (xorg_list_is_empty(&xwl_window->link_damage))
         xorg_list_add(&xwl_window->link_damage, &xwl_screen->damage_window_list);

hw/xwayland/xwayland-window.h

@@ -111,7 +111,6 @@ struct xwl_window {
     struct wl_output *wl_output;
     struct wl_output *wl_output_fullscreen;
     struct xorg_list frame_callback_list;
-    Bool present_flipped;
 #ifdef XWL_HAS_LIBDECOR
     struct libdecor_frame *libdecor_frame;
 #endif