[Mesa-dev] [PATCH 3/5] glx/dri3: Request non-vsynced Present for swapinterval zero. (v3)

[Mario Kleiner]

Restores proper immediate tearing swap behaviour for
OpenGL bufferswap under DRI3/Present.

Cc: "10.3 10.4" <mesa-stable at lists.freedesktop.org>

v2: Add Frank Binns signed off by for his original earlier
patch from April 2014, which is identical to this one, and
Chris Wilsons reviewed tag from May 2014 for that patch, ergo
also for this one.

v3: Incorporate comment about triple buffering as suggested
by Axel Davy, and reference to relevant spec provided by
Eric Anholt.

Signed-off-by: Frank Binns <frank.binns at imgtec.com>
Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
Reviewed-by: Axel Davy <axel.davy at ens.fr>
Reviewed-by: Eric Anholt <eric at anholt.net>
---
 src/glx/dri3_glx.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/glx/dri3_glx.c b/src/glx/dri3_glx.c
index b89cb46..3f5e64c 100644
--- a/src/glx/dri3_glx.c
+++ b/src/glx/dri3_glx.c
@@ -1526,6 +1526,7 @@ dri3_swap_buffers(__GLXDRIdrawable *pdraw, int64_t target_msc, int64_t divisor,
    xcb_connection_t *c = XGetXCBConnection(dpy);
    struct dri3_buffer *back;
    int64_t ret = 0;
+   uint32_t options = XCB_PRESENT_OPTION_NONE;
 
    unsigned flags = __DRI2_FLUSH_DRAWABLE;
    if (flush)
@@ -1565,6 +1566,17 @@ dri3_swap_buffers(__GLXDRIdrawable *pdraw, int64_t target_msc, int64_t divisor,
       if (target_msc == 0)
          target_msc = priv->msc + priv->swap_interval * (priv->send_sbc - priv->recv_sbc);
 
+      /* From the GLX_EXT_swap_control spec:
+       *
+       *     "If <interval> is set to a value of 0, buffer swaps are not
+       *      synchronized to a video frame."
+       *
+       * Implementation note: It is possible to enable triple buffering behaviour
+       * by not using XCB_PRESENT_OPTION_ASYNC, but this should not be the default.
+       */
+      if (priv->swap_interval == 0)
+          options |= XCB_PRESENT_OPTION_ASYNC;
+
       back->busy = 1;
       back->last_swap = priv->send_sbc;
       xcb_present_pixmap(c,
@@ -1578,7 +1590,7 @@ dri3_swap_buffers(__GLXDRIdrawable *pdraw, int64_t target_msc, int64_t divisor,
                          None,                                 /* target_crtc */
                          None,
                          back->sync_fence,
-                         XCB_PRESENT_OPTION_NONE,
+                         options,
                          target_msc,
                          divisor,
                          remainder, 0, NULL);
-- 
2.1.0