Send vsync timebase updates to the browser compositor

ui/gl/gl_surface_glx.cc

Index: ui/gl/gl_surface_glx.cc
diff --git a/ui/gl/gl_surface_glx.cc b/ui/gl/gl_surface_glx.cc
index 6e1675498ba3bfac0af052f9c28b0043ce37913c..001241118957ecf823df6482cfbe6a30602bf8ae 100644
--- a/ui/gl/gl_surface_glx.cc
+++ b/ui/gl/gl_surface_glx.cc
@@ -37,6 +37,7 @@ Display* g_display;
 const char* g_glx_extensions = NULL;
 bool g_glx_create_context_robustness_supported = false;
 bool g_glx_texture_from_pixmap_supported = false;
+bool g_glx_oml_sync_control_supported = false;
 
 }  // namespace
 
@@ -69,6 +70,8 @@ bool GLSurfaceGLX::InitializeOneOff() {
       HasGLXExtension("GLX_ARB_create_context_robustness");
   g_glx_texture_from_pixmap_supported =
       HasGLXExtension("GLX_EXT_texture_from_pixmap");
+  g_glx_oml_sync_control_supported =
+      HasGLXExtension("GLX_OML_sync_control");
 
   initialized = true;
   return true;
@@ -94,6 +97,11 @@ bool GLSurfaceGLX::IsTextureFromPixmapSupported() {
   return g_glx_texture_from_pixmap_supported;
 }
 
+// static
+bool GLSurfaceGLX::IsOMLSyncControlSupported() {
+  return g_glx_oml_sync_control_supported;
+}
+
 void* GLSurfaceGLX::GetDisplay() {
   return g_display;
 }
@@ -224,6 +232,40 @@ bool NativeViewGLSurfaceGLX::PostSubBuffer(
   return true;
 }
 
+bool NativeViewGLSurfaceGLX::GetSyncValues(int64* monotonicTime,
+                                           int64* mediaStreamCounter,
+                                           int64* swapBufferCounter) {
+  if (g_glx_oml_sync_control_supported) {
+    // Though the actual clock used for the system time returned by
+    // glXGetSyncValuesOML is unspecified, in practice it turns out to
+    // be CLOCK_REALTIME. We need the time according to CLOCK_MONOTONIC,

[piman, 2012/10/24 16:56:54]

Where did we test that assumption? Only Intel drivers, or others?

[ajuma, 2012/10/26 20:12:39]

Only on Intel (I haven't managed to get my hands on a non-Intel device that
supports this extension).

In the latest version, instead of assuming that the returned time is from
CLOCK_REALTIME, we instead try to determine if it's from CLOCK_REALTIME or
CLOCK_MONONTONIC (by checking if it's sufficiently close to the current time
according to either of these clocks).

+    // so we have to convert.
+    int64 systemTime;

[piman, 2012/10/24 16:56:54]

nit: chrome style, here and everywhere.

[ajuma, 2012/10/26 20:12:39]

Done.

+    if (glXGetSyncValuesOML(g_display, window_, &systemTime,
+                            mediaStreamCounter, swapBufferCounter)) {
+      struct timespec currentRealTime;
+      struct timespec currentMonotonicTime;
+      clock_gettime(CLOCK_REALTIME, &currentRealTime);
+      clock_gettime(CLOCK_MONOTONIC, &currentMonotonicTime);
+
+      int64 currentRealTimeInMicroseconds =
+          currentRealTime.tv_sec * base::Time::kMicrosecondsPerSecond +
+          currentRealTime.tv_nsec / base::Time::kNanosecondsPerMicrosecond;
+      int64 currentMonotonicTimeInMicroseconds =
+          currentMonotonicTime.tv_sec * base::Time::kMicrosecondsPerSecond +
+          currentMonotonicTime.tv_nsec / base::Time::kNanosecondsPerMicrosecond;
+
+      int64 timeDifference =
+          currentRealTimeInMicroseconds - currentMonotonicTimeInMicroseconds;
+      *monotonicTime = systemTime - timeDifference;
+
+      return true;
+    }
+  }
+
+  return false;
+}
+
 NativeViewGLSurfaceGLX::NativeViewGLSurfaceGLX()
   : window_(0),
     config_(NULL) {