[Cogl] [PATCH 1/2] kms-winsys: Defer setting new surfaces until swap buffers

[Rui Matos]

We can't just destroy and replace the EGL and gbm surfaces while
they are still in use i.e. while there is a pending flip. In fact, in
that case, we were calling gbm_surface_destroy() on a surface that
still had the front buffer locked and then, on the flip handler,
gbm_surface_release_buffer() for a buffer that didn't belong to the
new surface.

Instead, we still allocate new surfaces when requested but they only
replace the old ones on the next swap buffers when we're sure that the
previous flip has been handled and buffers properly released.
---
 cogl/winsys/cogl-winsys-egl-kms.c | 34 ++++++++++++++++++++++++++--------
 1 file changed, 26 insertions(+), 8 deletions(-)

diff --git a/cogl/winsys/cogl-winsys-egl-kms.c b/cogl/winsys/cogl-winsys-egl-kms.c
index 86f57c0..dbedb0c 100644
--- a/cogl/winsys/cogl-winsys-egl-kms.c
+++ b/cogl/winsys/cogl-winsys-egl-kms.c
@@ -110,6 +110,9 @@ typedef struct _CoglOnscreenKMS
   struct gbm_bo *current_bo;
   struct gbm_bo *next_bo;
   CoglBool pending_swap_notify;
+
+  EGLSurface *pending_egl_surface;
+  struct gbm_surface *pending_surface;
 } CoglOnscreenKMS;
 
 static const char device_name[] = "/dev/dri/card0";
@@ -868,10 +871,27 @@ _cogl_winsys_onscreen_swap_buffers_with_damage (CoglOnscreen *onscreen,
   while (kms_onscreen->next_fb_id != 0)
     handle_drm_event (kms_renderer);
 
+  if (kms_onscreen->pending_egl_surface)
+    {
+      eglDestroySurface (egl_renderer->edpy, egl_onscreen->egl_surface);
+      egl_onscreen->egl_surface = kms_onscreen->pending_egl_surface;
+      kms_onscreen->pending_egl_surface = NULL;
+
+      _cogl_framebuffer_winsys_update_size (COGL_FRAMEBUFFER (kms_display->onscreen),
+                                            kms_display->width, kms_display->height);
+      context->current_draw_buffer_changes |= COGL_FRAMEBUFFER_STATE_BIND;
+    }
   parent_vtable->onscreen_swap_buffers_with_damage (onscreen,
                                                     rectangles,
                                                     n_rectangles);
 
+  if (kms_onscreen->pending_surface)
+    {
+      free_current_bo (onscreen);
+      gbm_surface_destroy (kms_onscreen->surface);
+      kms_onscreen->surface = kms_onscreen->pending_surface;
+      kms_onscreen->pending_surface = NULL;
+    }
   /* Now we need to set the CRTC to whatever is the front buffer */
   kms_onscreen->next_bo = gbm_surface_lock_front_buffer (kms_onscreen->surface);
 
@@ -1177,7 +1197,6 @@ cogl_kms_display_set_layout (CoglDisplay *display,
        height != kms_display->height) &&
       kms_display->onscreen)
     {
-      CoglContext *context = COGL_FRAMEBUFFER (kms_display->onscreen)->context;
       CoglOnscreenEGL *egl_onscreen = kms_display->onscreen->winsys;
       CoglOnscreenKMS *kms_onscreen = egl_onscreen->platform;
       struct gbm_surface *new_surface;
@@ -1213,14 +1232,13 @@ cogl_kms_display_set_layout (CoglDisplay *display,
           return FALSE;
         }
 
-      eglDestroySurface (egl_renderer->edpy, egl_onscreen->egl_surface);
-      gbm_surface_destroy (kms_onscreen->surface);
-
-      kms_onscreen->surface = new_surface;
-      egl_onscreen->egl_surface = new_egl_surface;
+      if (kms_onscreen->pending_egl_surface)
+        eglDestroySurface (egl_renderer->edpy, kms_onscreen->pending_egl_surface);
+      if (kms_onscreen->pending_surface)
+        gbm_surface_destroy (kms_onscreen->pending_surface);
 
-      _cogl_framebuffer_winsys_update_size (COGL_FRAMEBUFFER (kms_display->onscreen), width, height);
-      context->current_draw_buffer_changes |= COGL_FRAMEBUFFER_STATE_BIND;
+      kms_onscreen->pending_surface = new_surface;
+      kms_onscreen->pending_egl_surface = new_egl_surface;
     }
 
   kms_display->width = width;
-- 
2.1.0