From 9bd87cb271fe2346f203655d01714bdb808f9ea8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lubo=C5=A1=20Lu=C5=88=C3=A1k?= <l.lunak@kde.org>
Date: Sun, 11 May 2008 12:03:42 +0000
Subject: [PATCH] Redo timing of next painting with vsync used, try harder not
 to miss every other sync just by a small time.

svn path=/trunk/KDE/kdebase/workspace/; revision=806443
---
 composite.cpp    | 18 +++++++-----------
 scene_opengl.cpp | 13 +++++++++++--
 2 files changed, 18 insertions(+), 13 deletions(-)

diff --git a/composite.cpp b/composite.cpp
index 25859793da..4157a38b92 100644
--- a/composite.cpp
+++ b/composite.cpp
@@ -175,8 +175,7 @@ void Workspace::setupCompositing()
     if( rate <= 0 )
         rate = 50;
     // QTimer gives us 1msec (1000Hz) at best, so we ignore anything higher;
-    // however, since compositing is limited to no more than once per 5msec,
-    // 200Hz to 1000Hz are effectively identical
+    // however, additional throttling makes prevents very high rates from taking place anyway
     else if( rate > 1000 )
         rate = 1000;
     kDebug( 1212 ) << "Refresh rate " << rate << "Hz";
@@ -318,15 +317,12 @@ void Workspace::performCompositing()
     // clear all repaints, so that post-pass can add repaints for the next repaint
     repaints_region = QRegion();
     scene->paint( repaints, windows );
-    if( scene->waitSyncAvailable() && options->glVSync )
-        { // if we're using vsync, then time the next paint pass to
-          // before the next available sync
-        int paintTime = ( lastCompositePaint.elapsed() % compositeRate ) +
-                        ( compositeRate / 2 );
-        if( paintTime >= compositeRate )
-            compositeTimer.start( paintTime );
-        else if( paintTime < compositeRate )
-            compositeTimer.start( compositeRate - paintTime );
+    if( scene->waitSyncAvailable())
+        {
+        // if vsync is used, schedule the next repaint slightly in advance of the next sync,
+        // so that there is still time for the drawing to take place
+        int untilNextSync = compositeRate - ( lastCompositePaint.elapsed() % compositeRate );
+        compositeTimer.start( qMax( 1, untilNextSync - 10 )); // 10 ms in advance - TODO maybe less?
         }
     lastCompositePaint.start();
 #endif
diff --git a/scene_opengl.cpp b/scene_opengl.cpp
index 5e6db2324f..53d5f5cff0 100644
--- a/scene_opengl.cpp
+++ b/scene_opengl.cpp
@@ -145,7 +145,16 @@ SceneOpenGL::SceneOpenGL( Workspace* ws )
     if( db )
         glDrawBuffer( GL_BACK );
     // Check whether certain features are supported
-    has_waitSync = glXGetVideoSync ? true : false;
+    has_waitSync = false;
+    if( glXGetVideoSync && glXIsDirect( display(), ctxbuffer ) && options->glVSync )
+        {
+        unsigned int sync;
+        if( glXGetVideoSync( &sync ) == 0 )
+            {
+            if( glXWaitVideoSync( 1, 0, &sync ) == 0 )
+                has_waitSync = true;
+            }
+        }
 
     // OpenGL scene setup
     glMatrixMode( GL_PROJECTION );
@@ -625,7 +634,7 @@ void SceneOpenGL::paint( QRegion damage, ToplevelList toplevels )
 // wait for vblank signal before painting
 void SceneOpenGL::waitSync()
     { // NOTE that vsync has no effect with indirect rendering
-    if( waitSyncAvailable() && options->glVSync )
+    if( waitSyncAvailable())
         {
         unsigned int sync;