gallium: more elaborate tracking of front color buffer state

This fixes the case where the app calls SwapBuffers then calls glReadPixels
to read the front color buffer.  We now keep track of when the front buffer
is a _logically_ copy of the back buffer (after SwapBuffers) and read from
the back color buffer instead of the front.

1 files changed, 4 insertions, 23 deletions

diff --git a/src/mesa/state_tracker/st_cb_flush.c b/src/mesa/state_tracker/st_cb_flush.c
index 1bcd1b4cd9..1b3402cee2 100644
--- a/src/mesa/state_tracker/st_cb_flush.c
+++ b/src/mesa/state_tracker/st_cb_flush.c
@@ -44,30 +44,10 @@
 #include "pipe/p_winsys.h"
 
 
-static GLboolean
+static INLINE GLboolean
 is_front_buffer_dirty(struct st_context *st)
 {
-   GLframebuffer *fb = st->ctx->DrawBuffer;
-
-   if (!fb)
-      return GL_FALSE;
-
-   /* XXX: temporary hack.  This flag should only be set if we do any
-    * rendering to the front buffer.
-    *
-    * Further more, the scissor rectangle could be tracked to
-    * construct a dirty region of the front buffer, to avoid
-    * situations where it must be copied repeatedly.
-    *
-    * In the extreme case, some kind of timer could be set up to allow
-    * coalescing of multiple flushes to the frontbuffer, which can be
-    * quite a performance drain if there are a sufficient number of
-    * them.
-    */
-   st->flags.frontbuffer_dirty
-      = (fb->_ColorDrawBufferMask[0] & BUFFER_BIT_FRONT_LEFT);
-
-   return st->flags.frontbuffer_dirty;
+   return st->frontbuffer_status == FRONT_STATUS_DIRTY;
 }
 
 
@@ -86,7 +66,8 @@ display_front_buffer(struct st_context *st)
     */
    st->pipe->winsys->flush_frontbuffer( st->pipe->winsys, front_surf,
                                         st->pipe->priv );
-   st->flags.frontbuffer_dirty = 0;
+
+   st->frontbuffer_status = FRONT_STATUS_UNDEFINED;
 }