[PATCH] ui/dbus: Implement damage regions for GL

[Bilal Elmoussaoui <belmouss@redhat.com>]

From: Christian Hergert <chergert@redhat.com>

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.

In the future, when additional methods are allowed on the D-Bus
interface,
this should likely be updated to send damage regions as a single RPC to
avoid additional message processing.

Currently, Linux does not propagate damage rectangles when using the
virtio-gpu drm driver. That means compositors such as Mutter which
utilize
drmModePageFlip() will be sending full or near-full surface damages.

https://lists.freedesktop.org/archives/dri-devel/2023-March/395164.html
contains a patch to fix that too.

Signed-off-by: Bilal Elmoussaoui <belmouss@redhat.com>
---
 meson.build        |  8 ++++++++
 ui/dbus-listener.c | 25 +++++++++++++++++++------
 ui/meson.build     |  2 +-
 3 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/meson.build b/meson.build
index 229eb585f7..72678ef78e 100644
--- a/meson.build
+++ b/meson.build
@@ -1761,6 +1761,14 @@ dbus_display = get_option('dbus_display') \
            error_message: '-display dbus is not available on Windows') \
   .allowed()
 
+cairo = not_found
+if dbus_display
+  cairo = dependency('cairo',
+                     kwargs: static_kwargs,
+                     method: 'pkg-config',
+                    )
+endif
+
 have_virtfs = get_option('virtfs') \
     .require(targetos == 'linux' or targetos == 'darwin',
              error_message: 'virtio-9p (virtfs) requires Linux or macOS') \
diff --git a/ui/dbus-listener.c b/ui/dbus-listener.c
index 911acdc529..047be5cb3a 100644
--- a/ui/dbus-listener.c
+++ b/ui/dbus-listener.c
@@ -25,6 +25,7 @@
 #include "qemu/error-report.h"
 #include "sysemu/sysemu.h"
 #include "dbus.h"
+#include <cairo.h>
 #include <gio/gunixfdlist.h>
 
 #ifdef CONFIG_OPENGL
@@ -43,9 +44,10 @@ struct _DBusDisplayListener {
 
     QemuDBusDisplay1Listener *proxy;
 
+    cairo_region_t *gl_damage;
+
     DisplayChangeListener dcl;
     DisplaySurface *ds;
-    int gl_updates;
 };
 
 G_DEFINE_TYPE(DBusDisplayListener, dbus_display_listener, G_TYPE_OBJECT)
@@ -226,10 +228,17 @@ static void dbus_gl_refresh(DisplayChangeListener *dcl)
         return;
     }
 
-    if (ddl->gl_updates) {
-        dbus_call_update_gl(ddl, 0, 0,
-                            surface_width(ddl->ds), surface_height(ddl->ds));
-        ddl->gl_updates = 0;
+    if (ddl->gl_damage) {
+        int n_rects = cairo_region_num_rectangles(ddl->gl_damage);
+
+        for (int i = 0; i < n_rects; i++) {
+            cairo_rectangle_int_t rect;
+
+            cairo_region_get_rectangle(ddl->gl_damage, i, &rect);
+            dbus_call_update_gl(ddl, rect.x, rect.y, rect.width, rect.height);
+        }
+
+        g_clear_pointer(&ddl->gl_damage, cairo_region_destroy);
     }
 }
 #endif
@@ -245,7 +254,11 @@ static void dbus_gl_gfx_update(DisplayChangeListener *dcl,
 {
     DBusDisplayListener *ddl = container_of(dcl, DBusDisplayListener, dcl);
 
-    ddl->gl_updates++;
+    if (ddl->gl_damage == NULL) {
+        ddl->gl_damage = cairo_region_create();
+    }
+    cairo_region_union_rectangle(ddl->gl_damage,
+                                 &(cairo_rectangle_int_t) {x, y, w, h});
 }
 #endif
 
diff --git a/ui/meson.build b/ui/meson.build
index 330369707d..8b4004ff01 100644
--- a/ui/meson.build
+++ b/ui/meson.build
@@ -85,7 +85,7 @@ if dbus_display
                                           '--generate-c-code', '@BASENAME@'])
   dbus_display1_lib = static_library('dbus-display1', dbus_display1, dependencies: gio)
   dbus_display1_dep = declare_dependency(link_with: dbus_display1_lib, include_directories: include_directories('.'))
-  dbus_ss.add(when: [gio, pixman, dbus_display1_dep],
+  dbus_ss.add(when: [gio, pixman, dbus_display1_dep, cairo],
               if_true: [files(
                 'dbus-chardev.c',
                 'dbus-clipboard.c',
-- 
2.40.0