Only enable vsync if a compositing window manager is not in use. This

restores performance and latency on Linux to previous levels before
the bug fix enabling vsync for the first time.

Tested manually both with and without Compiz enabled and verified the
detection logic works.

BUG=81333
TEST=none
Review URL: http://codereview.chromium.org/6911030

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@83921 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 20 insertions, 1 deletions

diff --git a/ui/gfx/gl/gl_context_linux.cc b/ui/gfx/gl/gl_context_linux.cc
index 36f0e8a..bf0b75e 100644
--- a/ui/gfx/gl/gl_context_linux.cc
+++ b/ui/gfx/gl/gl_context_linux.cc
@@ -37,6 +37,19 @@ Display* GetXDisplayHelper() {
   return display;
 }
 
+bool IsCompositingWindowManagerActive(Display* display) {
+  // The X macro "None" has been undefined by gl_bindings.h.
+  const int kNone = 0;
+  static Atom net_wm_cm_s0 = kNone;
+  if (net_wm_cm_s0 == kNone) {
+    net_wm_cm_s0 = XInternAtom(display, "_NET_WM_CM_S0", True);
+  }
+  if (net_wm_cm_s0 == kNone) {
+    return false;
+  }
+  return XGetSelectionOwner(display, net_wm_cm_s0) != kNone;
+}
+
 }  // namespace
 
 namespace gfx {
@@ -335,7 +348,13 @@ void ViewGLContext::SetSwapInterval(int interval) {
   DCHECK(IsCurrent());
   if (HasExtension("GLX_EXT_swap_control") && glXSwapIntervalEXT) {
     Display* display = GetXDisplayHelper();
-    glXSwapIntervalEXT(display, window_, interval);
+    // Only enable vsync if we aren't using a compositing window
+    // manager. At the moment, compositing window managers don't
+    // respect this setting anyway (tearing still occurs) and it
+    // dramatically increases latency.
+    if (!IsCompositingWindowManagerActive(display)) {
+      glXSwapIntervalEXT(display, window_, interval);
+    }
   }
 }