mesa/st: Reduce the number of frontbuffer flush calls

The mesa state tracker was needlessly flushing the front buffer even if it
hadn't been drawn to since the last flush. This was happening during
glXSwapBuffers if we at some point previously had set that frontbuffer as
a read- or draw renderbuffer, or at glFlush() or glFinish() if we at some
point previously had rendered to the front buffer. Since the frontbuffer
flush typically means a full drawable copy, it's a pretty big waste.

Signed-off-by: Thomas Hellstrom <[email protected]>
Reviewed-by: Marek Olšák <[email protected]>
Reviewed-by: Sinclair Yeh <[email protected]>

1 files changed, 8 insertions, 4 deletions

diff --git a/src/mesa/state_tracker/st_manager.c b/src/mesa/state_tracker/st_manager.c
index 62924b099e9..28cf0234cd6 100644
--- a/src/mesa/state_tracker/st_manager.c
+++ b/src/mesa/state_tracker/st_manager.c
@@ -1036,11 +1036,15 @@ st_manager_flush_frontbuffer(struct st_context *st)
 
    if (stfb)
       strb = st_renderbuffer(stfb->Base.Attachment[BUFFER_FRONT_LEFT].Renderbuffer);
-   if (!strb)
-      return;
 
-   /* never a dummy fb */
-   stfb->iface->flush_front(&st->iface, stfb->iface, ST_ATTACHMENT_FRONT_LEFT);
+   /* Do we have a front color buffer and has it been drawn to since last
+    * frontbuffer flush?
+    */
+   if (strb && strb->defined) {
+      stfb->iface->flush_front(&st->iface, stfb->iface,
+                               ST_ATTACHMENT_FRONT_LEFT);
+      strb->defined = GL_FALSE;
+   }
 }
 
 /**