[Mesa-dev] [PATCH 4/5] glx/dri3: Don't fail on glXSwapBuffersMscOML(dpy, window, 0, 0, 0)

[Mario Kleiner]

glXSwapBuffersMscOML() with target_msc=divisor=remainder=0 gets
translated into target_msc=divisor=0 but remainder=1 by the mesa
api. This is done for server DRI2 where there needs to be a way
to tell the server-side DRI2ScheduleSwap implementation if a call
to glXSwapBuffers() or glXSwapBuffersMscOML(dpy,window,0,0,0) was
done. remainder = 1 was (ab)used as a flag to tell the server to
select proper semantic. The DRI3/Present backend ignored this
signalling, treated any target_msc=0 as glXSwapBuffers() request,
and called xcb_present_pixmap with invalid divisor=0, remainder=1
combo. The present extension responded kindly to this with a
BadValue error and dropped the request, but mesa's DRI3/Present
backend doesn't check for error codes. From there on stuff went
downhill quickly for the calling OpenGL client...

This patch fixes the problem.

Cc: "10.3 10.4" <mesa-stable at lists.freedesktop.org>
Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
---
 src/glx/dri3_glx.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/glx/dri3_glx.c b/src/glx/dri3_glx.c
index c53be1b..efff907 100644
--- a/src/glx/dri3_glx.c
+++ b/src/glx/dri3_glx.c
@@ -1552,11 +1552,21 @@ dri3_swap_buffers(__GLXDRIdrawable *pdraw, int64_t target_msc, int64_t divisor,
       dri3_fence_reset(c, back);
 
       /* Compute when we want the frame shown by taking the last known successful
-       * MSC and adding in a swap interval for each outstanding swap request
+       * MSC and adding in a swap interval for each outstanding swap request.
+       * target_msc=divisor=remainder=0 means "Use glXSwapBuffers() semantic"
        */
       ++priv->send_sbc;
-      if (target_msc == 0)
+      if (target_msc == 0 && divisor == 0 && remainder == 0)
          target_msc = priv->msc + priv->swap_interval * (priv->send_sbc - priv->recv_sbc);
+      else if (divisor == 0 && remainder > 0) {
+         /* Special case signalling: This means "glXSwapBuffersMscOML() called with
+          * target_msc=divisor=remainder=0. Needed to distinguish from glXSwapBuffers
+          * case above. Reset remainder to zero, so PresentPixmap won't bail on us.
+          * GLX_OML_sync_control says for divisor == 0 any remainder >= 0 is fine,
+          * whereas Present extension wants remainder == 0 for divisor == 0.
+          */
+         remainder = 0;
+      }
 
       if (priv->swap_interval == 0)
           options |= XCB_PRESENT_OPTION_ASYNC;
-- 
1.9.1