graphics/mesa-libs: Change default to use DRI3

Change the default mesa configuration to use DRI3 rather than the older DRI2
interface.  This should improve performance somewhat, and alleviates the need
for the FIXDRM option in x11-servers/xorg-server.

Remove the FIXDRM option from x11-servers/xorg-server.

Add an UPDATING entry for the change.

For users of graphics/drm-legacy-kmod or the base graphics drivers, this might
cause regressions.  If you experience problems when running OpenGL applications
please force the use of the DRI2 backend by setting the LIBGL_DRI3_DISABLE
environment variable to 1 before starting any OpenGL application.  This is
easiest done by adding it to your shell startup file or .xinitrc.

Add UPDATING entry for xorg-server, detailing the change of device
configuration backend.

PR:		196678, 244306 (for tracking)

1 files changed, 14 insertions, 0 deletions

diff --git a/UPDATING b/UPDATING
index 14a74f639535..12a6e5da20f9 100644
--- a/UPDATING
+++ b/UPDATING
@@ -5,6 +5,20 @@ they are unavoidable.
 You should get into the habit of checking this file for changes each time
 you update your ports collection, before attempting any port upgrades.
 
+20200308
+  AFFECTS: users of graphics/mesa-libs and legacy graphics drivers
+  AUTHOR: zeising@FreeBSD.org
+
+  The mesa OpenGL library (graphics/mesa-libs) has been switched to use DRI3
+  by default, instead of the older DRI2 interface.  This might cause regressions
+  when using the legacy graphics drivers, either through
+  graphics/drm-legacy-kmod or the graphics drivers in base.
+  
+  If you experience issues when running OpenGL applications it is possible
+  to force the use of DRI2 by setting the LIBGL_DRI3_DISABLE environment
+  variable to 1 before starting any OpenGL application.  The easiest way to
+  do this is by adding it to either your shell startup files or .xinitrc.
+
 20200306
   AFFECTS: users of databases/mysql80-server
   AUTHOR: joneum@FreeBSD.org