Get high resolution frame timebase and interval on compatible systems

ui/gl/gl_surface_win.cc

Index: ui/gl/gl_surface_win.cc
diff --git a/ui/gl/gl_surface_win.cc b/ui/gl/gl_surface_win.cc
index 2219f32c0386efb8bc3a3bbc03f3dba9adce1ce1..3d033a4a23e5c5ff063f2d19b36aed8df8d9d6ac 100644
--- a/ui/gl/gl_surface_win.cc
+++ b/ui/gl/gl_surface_win.cc
@@ -91,44 +91,37 @@ class WinVSyncProvider : public VSyncProvider {
         if (gfx::FrameTime::TimestampsAreHighRes()) {
           timebase = gfx::FrameTime::FromQPCValue(
               static_cast<LONGLONG>(timing_info.qpcVBlank));
-        }
-
-        // Swap the numerator/denominator to convert frequency to period.
-        if (timing_info.rateRefresh.uiDenominator > 0 &&
+          interval = base::TimeDelta::FromQPCValue(
+              static_cast<LONGLONG>(timing_info.qpcRefreshPeriod));

[brianderson, 2014/10/22 23:05:30]

+tansell for fyi: Apparently qpcRefreshPeriod is a bit noisy compared to the
Numerator/Denominator calculation below. Would definitely benefit from the vsync
filtering you want to work on.

+        } else if (timing_info.rateRefresh.uiDenominator > 0 &&
             timing_info.rateRefresh.uiNumerator > 0) {
+          // Swap the numerator/denominator to convert frequency to period.

[brianderson, 2014/10/22 23:05:30]

Can you add some comments regarding why you don't use the qpcRefreshPeriod when
we don't have HighRes timestamps.

           interval = base::TimeDelta::FromMicroseconds(
               timing_info.rateRefresh.uiDenominator *
               base::Time::kMicrosecondsPerSecond /
               timing_info.rateRefresh.uiNumerator);
         }
       }
-    }
-
-    // Double check DWM values against per-display refresh rates.
-    // When DWM compositing is active all displays are normalized to the
-    // refresh rate of the primary display, and won't composite any faster.
-    // If the display refresh rate is higher than the DWM reported value we will
-    // favor the DWM value because any additional frames produced will be
-    // discarded by the OS. If the display refresh rate is lower, however, we
-    // can use that to limit the frames we produce more intelligently.
-    // If DWM compositing is not active we will always use the display refresh.
-    HMONITOR monitor = MonitorFromWindow(window_, MONITOR_DEFAULTTONEAREST);
-    MONITORINFOEX monitor_info;
-    monitor_info.cbSize = sizeof(MONITORINFOEX);
-    BOOL result = GetMonitorInfo(monitor, &monitor_info);
-    if (result) {
-      DEVMODE display_info;
-      display_info.dmSize = sizeof(DEVMODE);
-      display_info.dmDriverExtra = 0;
-      result = EnumDisplaySettings(monitor_info.szDevice, ENUM_CURRENT_SETTINGS,
-          &display_info);
-      if (result && display_info.dmDisplayFrequency > 1) {
-        base::TimeDelta display_interval = base::TimeDelta::FromMicroseconds(
-            (1.0 / static_cast<double>(display_info.dmDisplayFrequency)) *
-            base::Time::kMicrosecondsPerSecond);
-
-        if (!dwm_active || display_interval > interval) {
-          interval = display_interval;
+    } else {
+      // When DWM compositing is active all displays are normalized to the
+      // refresh rate of the primary display, and won't composite any faster.
+      // If DWM compositing is disabled, though, we can use the refresh rates
+      // reported by each display, which will help systems that have mis-matched
+      // displays that run at different frequencies.
+      HMONITOR monitor = MonitorFromWindow(window_, MONITOR_DEFAULTTONEAREST);
+      MONITORINFOEX monitor_info;
+      monitor_info.cbSize = sizeof(MONITORINFOEX);
+      BOOL result = GetMonitorInfo(monitor, &monitor_info);
+      if (result) {
+        DEVMODE display_info;
+        display_info.dmSize = sizeof(DEVMODE);
+        display_info.dmDriverExtra = 0;
+        result = EnumDisplaySettings(monitor_info.szDevice,
+            ENUM_CURRENT_SETTINGS, &display_info);
+        if (result && display_info.dmDisplayFrequency > 1) {
+          interval = base::TimeDelta::FromMicroseconds(
+              (1.0 / static_cast<double>(display_info.dmDisplayFrequency)) *
+              base::Time::kMicrosecondsPerSecond);
         }
       }
     }