Mesa (master): st/wgl: check for negative delta in wait_swap_interval()

[Brian Paul]

Module: Mesa
Branch: master
Commit: d90e05ad487e9fe7e17c293814ac8549d9d686d8
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=d90e05ad487e9fe7e17c293814ac8549d9d686d8

Author: Frank Richter <frank.richter at dynardo.de>
Date:   Mon Aug 14 16:05:22 2017 +0200

st/wgl: check for negative delta in wait_swap_interval()

This can happen because of rollover.  See bug report for details.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102241
Cc: mesa-stable at lists.freedesktop.org
Reviewed-by: Brian Paul <brianp at vmware.com>
Reviewed-by: Jose Fonseca <jfonseca at vmware.com>

---

 src/gallium/state_trackers/wgl/stw_framebuffer.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/gallium/state_trackers/wgl/stw_framebuffer.c b/src/gallium/state_trackers/wgl/stw_framebuffer.c
index 321fbb6ea7..06b5c8da3c 100644
--- a/src/gallium/state_trackers/wgl/stw_framebuffer.c
+++ b/src/gallium/state_trackers/wgl/stw_framebuffer.c
@@ -601,8 +601,11 @@ wait_swap_interval(struct stw_framebuffer *fb)
       int64_t min_swap_period =
          1.0e6 / stw_dev->refresh_rate * stw_dev->swap_interval;
 
-      /* if time since last swap is less than wait period, wait */
-      if (delta < min_swap_period) {
+      /* If time since last swap is less than wait period, wait.
+       * Note that it's possible for the delta to be negative because of
+       * rollover.  See https://bugs.freedesktop.org/show_bug.cgi?id=102241
+       */
+      if ((delta >= 0) && (delta < min_swap_period)) {
          float fudge = 1.75f;  /* emperical fudge factor */
          int64_t wait = (min_swap_period - delta) * fudge;
          os_time_sleep(wait);