[cogl/wip/neil/snippets] framebuffer: Handle a NULL previous framebuffer when flushing

[Neil Roberts <nroberts src gnome org>]

commit 0c1cb332ef29c78706f33e18f0b05e91b3e51fb9
Author: Neil Roberts <neil linux intel com>
Date:   Thu Dec 1 18:46:37 2011 +0000

    framebuffer: Handle a NULL previous framebuffer when flushing
    
    _cogl_framebuffer_flush_state needs to handle the case where
    ctx->current_draw_buffer is NULL because this will be set in the
    destructor for CoglFramebuffer if the framebuffer being destroyed is
    the current framebuffer. This patch just makes it assume all state has
    changed in that case.

 cogl/cogl-framebuffer.c |   21 +++++++++++++++------
 1 files changed, 15 insertions(+), 6 deletions(-)
---
diff --git a/cogl/cogl-framebuffer.c b/cogl/cogl-framebuffer.c
index e4a4ce3..f70657c 100644
--- a/cogl/cogl-framebuffer.c
+++ b/cogl/cogl-framebuffer.c
@@ -1613,12 +1613,21 @@ _cogl_framebuffer_flush_state (CoglFramebuffer *draw_buffer,
 
   if (ctx->current_draw_buffer != draw_buffer)
     {
-      /* NB: we only need to compare the state we're being asked to flush
-       * and we don't need to compare the state we've already decided
-       * we will definitely flush... */
-      differences |= _cogl_framebuffer_compare (ctx->current_draw_buffer,
-                                                draw_buffer,
-                                                state & ~differences);
+      /* If the previous draw buffer is NULL then we'll assume
+         everything has changed. This can happen if a framebuffer is
+         destroyed while it is the last flushed draw buffer. In that
+         case the framebuffer destructor will set
+         ctx->current_draw_buffer to NULL */
+      if (ctx->current_draw_buffer == NULL)
+        differences |= state;
+      else
+        /* NB: we only need to compare the state we're being asked to flush
+         * and we don't need to compare the state we've already decided
+         * we will definitely flush... */
+        differences |= _cogl_framebuffer_compare (ctx->current_draw_buffer,
+                                                  draw_buffer,
+                                                  state & ~differences);
+
       /* NB: we don't take a reference here, to avoid a circular
        * reference. */
       ctx->current_draw_buffer = draw_buffer;