[cogl/cogl-1.8] Don't take a reference to the last used onscreen framebuffer

[Neil Roberts <nroberts src gnome org>]

commit 4b4eb53658a3f0fca25212a16b5bbdc485d23be6
Author: Neil Roberts <neil linux intel com>
Date:   Mon Nov 14 15:09:13 2011 +0000

    Don't take a reference to the last used onscreen framebuffer
    
    Cogl keeps a pointer to the last used onscreen framebuffer from the
    context to implement the deprecated cogl_set_draw_buffer function
    which can take COGL_WINDOW_BUFFER as the target to use the last
    onscreen buffer. Previously this would also take a reference to that
    pointer. However that was causing a circular reference between the
    framebuffer and the context which makes it impossible to clean up
    resources properly when onscreen buffers are used. This patch instead
    changes it to just store the pointer and then clear the pointer during
    _cogl_onscreen_free as a kind of cheap weak reference.
    
    Reviewed-by: Robert Bragg <robert linux intel com>
    
    (cherry-pick from commit 39ca3e51dfaa652ae4a0d936fff32a5edaca6c5f)

 cogl/cogl-context.c     |    6 ------
 cogl/cogl-framebuffer.c |   21 +++++++++++----------
 2 files changed, 11 insertions(+), 16 deletions(-)
---
diff --git a/cogl/cogl-context.c b/cogl/cogl-context.c
index b44a748..f6dea4c 100644
--- a/cogl/cogl-context.c
+++ b/cogl/cogl-context.c
@@ -396,12 +396,6 @@ _cogl_context_free (CoglContext *context)
 
   winsys->context_deinit (context);
 
-  if (context->window_buffer)
-    {
-      cogl_object_unref (context->window_buffer);
-      context->window_buffer = NULL;
-    }
-
   _cogl_free_framebuffer_stack (context->framebuffer_stack);
 
   if (context->current_path)
diff --git a/cogl/cogl-framebuffer.c b/cogl/cogl-framebuffer.c
index e086e10..c6fab3c 100644
--- a/cogl/cogl-framebuffer.c
+++ b/cogl/cogl-framebuffer.c
@@ -1042,6 +1042,9 @@ _cogl_onscreen_free (CoglOnscreen *onscreen)
   CoglFramebuffer *framebuffer = COGL_FRAMEBUFFER (onscreen);
   const CoglWinsysVtable *winsys = _cogl_framebuffer_get_winsys (framebuffer);
 
+  if (framebuffer->context->window_buffer == onscreen)
+    framebuffer->context->window_buffer = NULL;
+
   winsys->onscreen_deinit (onscreen);
   g_return_if_fail (onscreen->winsys == NULL);
 
@@ -1172,18 +1175,16 @@ notify_buffers_changed (CoglFramebuffer *old_draw_buffer,
         }
     }
 
-  /* XXX:
-   * To support the deprecated cogl_set_draw_buffer API we keep track
-   * of the last onscreen framebuffer that was set so that it can
-   * be restored if the COGL_WINDOW_BUFFER enum is used. */
+  /* XXX: To support the deprecated cogl_set_draw_buffer API we keep
+   * track of the last onscreen framebuffer that was set so that it
+   * can be restored if the COGL_WINDOW_BUFFER enum is used. A
+   * reference isn't taken to the framebuffer because otherwise we
+   * would have a circular reference between the context and the
+   * framebuffer. Instead the pointer is set to NULL in
+   * _cogl_onscreen_free as a kind of a cheap weak reference */
   if (new_draw_buffer &&
       new_draw_buffer->type == COGL_FRAMEBUFFER_TYPE_ONSCREEN)
-    {
-      cogl_object_ref (new_draw_buffer);
-      if (ctx->window_buffer)
-        cogl_object_unref (ctx->window_buffer);
-      ctx->window_buffer = new_draw_buffer;
-    }
+    ctx->window_buffer = new_draw_buffer;
 }
 
 /* Set the current framebuffer without checking if it's already the