ui/dbus: implement damage regions for GL

Currently, when using `-display dbus,gl=on` all updates to the client
become "full scanout" updates, meaning there is no way for the client to
limit damage regions to the display server.

Instead of using an "update count", this patch tracks the damage region
and propagates it to the client.

This was less of an issue when clients were using GtkGLArea for
rendering,
as you'd be doing full-surface redraw. To be efficient, the client needs
both a DMA-BUF and the damage region to be updated.

Co-authored-by: Christian Hergert <chergert@redhat.com>
Signed-off-by: Bilal Elmoussaoui <belmouss@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230814125802.102160-1-belmouss@redhat.com>

ui/dbus-listener.c

@@ -26,6 +26,9 @@
 #include "qapi/error.h"
 #include "sysemu/sysemu.h"
 #include "dbus.h"
+#ifdef CONFIG_OPENGL
+#include <pixman.h>
+#endif
 #ifdef G_OS_UNIX
 #include <gio/gunixfdlist.h>
 #endif
@@ -59,12 +62,15 @@ struct _DBusDisplayListener {
 
     QemuDBusDisplay1Listener *proxy;
 
+#ifdef CONFIG_OPENGL
+    /* Keep track of the damage region */
+    pixman_region32_t gl_damage;
+#endif
+
     DisplayChangeListener dcl;
     DisplaySurface *ds;
     enum share_kind ds_share;
 
-    int gl_updates;
-
     bool ds_mapped;
     bool can_share_map;
 
@@ -539,11 +545,16 @@ static void dbus_gl_refresh(DisplayChangeListener *dcl)
         return;
     }
 
-    if (ddl->gl_updates) {
-        dbus_call_update_gl(dcl, 0, 0,
-                            surface_width(ddl->ds), surface_height(ddl->ds));
-        ddl->gl_updates = 0;
+    int n_rects = pixman_region32_n_rects(&ddl->gl_damage);
+
+    for (int i = 0; i < n_rects; i++) {
+        pixman_box32_t *box;
+        box = pixman_region32_rectangles(&ddl->gl_damage, NULL) + i;
+        /* TODO: Add a UpdateList call to send multiple updates at once */
+        dbus_call_update_gl(dcl, box->x1, box->y1,
+                            box->x2 - box->x1, box->y2 - box->y1);
     }
+    pixman_region32_clear(&ddl->gl_damage);
 }
 #endif /* OPENGL */
 
@@ -558,7 +569,10 @@ static void dbus_gl_gfx_update(DisplayChangeListener *dcl,
 {
     DBusDisplayListener *ddl = container_of(dcl, DBusDisplayListener, dcl);
 
-    ddl->gl_updates++;
+    pixman_region32_t rect_region;
+    pixman_region32_init_rect(&rect_region, x, y, w, h);
+    pixman_region32_union(&ddl->gl_damage, &ddl->gl_damage, &rect_region);
+    pixman_region32_fini(&rect_region);
 }
 #endif
 
@@ -738,6 +752,7 @@ dbus_display_listener_dispose(GObject *object)
     g_clear_object(&ddl->d3d11_proxy);
     g_clear_pointer(&ddl->peer_process, CloseHandle);
 #ifdef CONFIG_OPENGL
+    pixman_region32_fini(&ddl->gl_damage);
     egl_fb_destroy(&ddl->fb);
 #endif
 #endif
@@ -772,6 +787,9 @@ dbus_display_listener_class_init(DBusDisplayListenerClass *klass)
 static void
 dbus_display_listener_init(DBusDisplayListener *ddl)
 {
+#ifdef CONFIG_OPENGL
+    pixman_region32_init(&ddl->gl_damage);
+#endif
 }
 
 const char *