Merge lp:~vanvugt/compiz/fastSwapInterval into lp:compiz/0.9.8

[Daniel van Vugt]

Don't call glXSwapInterval on every frame when you don't need to.
Apparently doing so is slow for some people (LP: #1051286)

Don't call glXSwapInterval on every frame when you don't need to.
Apparently doing so is slow for some people (LP: #1051286)

[jenkins (martin-mrazik+qa)]

PASSED: Continuous integration, rev:3386
http://jenkins.qa.ubuntu.com/job/compiz-ci/109/
Executed test runs:
    SUCCESS: http://jenkins.qa.ubuntu.com/job/compiz-ci/./build=pbuilder,distribution=quantal,flavor=amd64/109/console

review: Approve (continuous-integration)

[Sam Spilsbury (smspillaz)]

I'm a bit eh about merging code without tests, but better in than out.

review: Approve

=== modified file 'plugins/opengl/src/screen.cpp'
--- plugins/opengl/src/screen.cpp	2012-09-20 09:35:40 +0000
+++ plugins/opengl/src/screen.cpp	2012-09-25 04:15:29 +0000
@@ -1674,6 +1674,17 @@
 {
 
 void
+fastSwapInterval (int interval)
+{
+    static int prev = -1;
+    if (GL::swapInterval && interval != prev)
+    {
+	(*GL::swapInterval) (interval);
+	prev = interval;
+    }
+}
+
+void
 waitForVideoSync ()
 {
 #ifndef USE_GLES
@@ -1681,8 +1692,7 @@
     if (GL::waitVideoSync)
     {
 	// Don't wait twice. Just in case.
-	if (GL::swapInterval)
-	    (*GL::swapInterval) (0);
+	fastSwapInterval (0);
 
 	/*
 	 * While glXSwapBuffers/glXCopySubBufferMESA are meant to do a
@@ -1711,7 +1721,7 @@
     // Docs: http://www.opengl.org/registry/specs/SGI/swap_control.txt
     if (GL::swapInterval)
     {
-	(*GL::swapInterval) (sync ? 1 : 0);
+	fastSwapInterval (sync ? 1 : 0);
 	GL::unthrottledFrames++;
     }
     else if (sync)