[cogl] framebuffer: Handle a NULL previous framebuffer when flushing

[Robert Bragg <rbragg src gnome org>]

commit 0c82c296bf15d40b54739d46d82f38d40e58f522
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.
    
    Reviewed-by: Robert Bragg <robert linux intel com>

 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 f8fc101..eaa0be7 100644
--- a/cogl/cogl-framebuffer.c
+++ b/cogl/cogl-framebuffer.c
@@ -1615,12 +1615,21 @@ _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;