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)

2 files changed, 11 insertions, 16 deletions

diff --git a/cogl/cogl-context.c b/cogl/cogl-context.c
index b44a748e..f6dea4cb 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 e086e106..c6fab3c6 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