st: added st_renderbuffer::defined flag

Indicates whether there's defined image contents, or garbage/don't care.
This is set when we draw into a renderbuffer and cleared when we resize/
reallocate a renderbuffer or do a buffer swap (back buffer becomes undefined).

We use this to determine whether the front color buffer has been drawn to,
and whether to display its contents upon glFlush/Finish(), when the new
st_swapbuffers() function is used.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/mesa/state_tracker/st_framebuffer.c b/src/mesa/state_tracker/st_framebuffer.c
index 07ccaa6aab..639373fff7 100644
--- a/src/mesa/state_tracker/st_framebuffer.c
+++ b/src/mesa/state_tracker/st_framebuffer.c
@@ -331,6 +331,12 @@ st_swapbuffers(struct st_framebuffer *stfb,
             st_renderbuffer(fb->Attachment[BUFFER_FRONT_LEFT].Renderbuffer);
          *front_left = strb->surface;
       }
+      /* mark back buffer contents as undefined */
+      {
+         struct st_renderbuffer *back =
+            st_renderbuffer(fb->Attachment[BUFFER_BACK_LEFT].Renderbuffer);
+         back->defined = GL_FALSE;
+      }
    }
    else {
       /* no front buffer, display the back buffer */
@@ -354,6 +360,12 @@ st_swapbuffers(struct st_framebuffer *stfb,
             st_renderbuffer(fb->Attachment[BUFFER_FRONT_RIGHT].Renderbuffer);
          *front_right = strb->surface;
       }
+      /* mark back buffer contents as undefined */
+      {
+         struct st_renderbuffer *back =
+            st_renderbuffer(fb->Attachment[BUFFER_BACK_RIGHT].Renderbuffer);
+         back->defined = GL_FALSE;
+      }
    }
    else {
       /* no front right buffer, display back right buffer (if exists) */