Let's go without __GL_YIELD by default for now.

svn path=/trunk/KDE/kdebase/workspace/; revision=756724

NOTES_4_0

@@ -7,6 +7,14 @@ This document is for creating the 4.0 release notes. There are 3 parts:
 =================
 
 
+- Performance/smoothness with nVidia cards: Smoothness of KWin rendering
+  can be improved by setting env.variable KWIN_NVIDIA_HACK to 1 (e.g. append
+  "export KWIN_NVIDIA_HACK=1" to your ~/.profile file). This sets __GL_YIELD=NOTHING
+  for KWin, letting KWin use more CPU time for OpenGL operations, however
+  at the expense of affecting performance of other applications. This is
+  therefore disabled by default. This setting may be removed in the future
+  if the negative impact becomes insignificant. See section "OPENGL YIELD BEHAVIOR"
+  in README.txt for nVidia cards.
 
 Comments
 ========

nvidiahack.cpp

@@ -32,7 +32,14 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 class kwinnvidiahack
     {
     public:
-        kwinnvidiahack() { setenv( "__GL_YIELD", "NOTHING", true ); }
+        kwinnvidiahack();
     };
 
+kwinnvidiahack::kwinnvidiahack()
+    {
+    const char* env = getenv( "KWIN_NVIDIA_HACK" );
+    if( env != NULL && env[ 0 ] != '0' )
+        setenv( "__GL_YIELD", "NOTHING", true );
+    }
+
 kwinnvidiahack kwinnvidiahackinst;