glx/dri3: Request non-vsynced Present for swapinterval zero. (v3)

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

Cc: "10.3 10.4" <mesa-stable@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@imgtec.com>
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Axel Davy <axel.davy@ens.fr>
Reviewed-by: Eric Anholt <eric@anholt.net>

diff --git a/src/glx/dri3_glx.c b/src/glx/dri3_glx.c
index b89cb4636548c0bf2c0571e13b3f419e55a66ef0..3f5e64c2a1efef9c575e28c3d4942002034c5bc8 100644 (file)
--- 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);