Bug 1628137 - Switch to using WaitForVBlank for vsync on Windows r=jrmuizel

Differential Revision: https://phabricator.services.mozilla.com/D70463

--HG--
extra : moz-landing-system : lando

gfx/thebes/DeviceManagerDx.cpp

@@ -170,6 +170,34 @@ nsTArray<DXGI_OUTPUT_DESC1> DeviceManagerDx::EnumerateOutputs() {
   return outputs;
 }
 
+bool DeviceManagerDx::GetOutputFromMonitor(HMONITOR monitor,
+                                           RefPtr<IDXGIOutput>* aOutOutput) {
+  RefPtr<IDXGIAdapter> adapter = GetDXGIAdapter();
+
+  if (!adapter) {
+    NS_WARNING("Failed to acquire a DXGI adapter for GetOutputFromMonitor.");
+    return false;
+  }
+
+  for (UINT i = 0;; ++i) {
+    RefPtr<IDXGIOutput> output = nullptr;
+    if (FAILED(adapter->EnumOutputs(i, getter_AddRefs(output)))) {
+      break;
+    }
+
+    DXGI_OUTPUT_DESC desc;
+    if (FAILED(output->GetDesc(&desc))) {
+      continue;
+    }
+
+    if (desc.Monitor == monitor) {
+      *aOutOutput = output;
+      return true;
+    }
+  }
+  return false;
+}
+
 bool DeviceManagerDx::CheckHardwareStretchingSupport() {
   RefPtr<IDXGIAdapter> adapter = GetDXGIAdapter();
 

gfx/thebes/DeviceManagerDx.h

@@ -87,6 +87,10 @@ class DeviceManagerDx final {
   // Enumerate and return all outputs on the current adapter.
   nsTArray<DXGI_OUTPUT_DESC1> EnumerateOutputs();
 
+  // find the IDXGIOutput with a description.Monitor matching
+  // 'monitor'; returns false if not found or some error occurred.
+  bool GetOutputFromMonitor(HMONITOR monitor, RefPtr<IDXGIOutput>* aOutOutput);
+
   // Check if the current adapter supports hardware stretching
   bool CheckHardwareStretchingSupport();
 

gfx/thebes/gfxWindowsPlatform.cpp

@@ -1621,7 +1621,8 @@ class D3DVsyncSource final : public VsyncSource {
     D3DVsyncDisplay()
         : mPrevVsync(TimeStamp::Now()),
           mVsyncEnabledLock("D3DVsyncEnabledLock"),
-          mVsyncEnabled(false) {
+          mVsyncEnabled(false),
+          mWaitVBlankMonitor(NULL) {
       mVsyncThread = new base::Thread("WindowsVsyncThread");
       MOZ_RELEASE_ASSERT(mVsyncThread->Start(),
                          "GFX: Could not start Windows vsync thread");
@@ -1796,9 +1797,16 @@ class D3DVsyncSource final : public VsyncSource {
           return;
         }
 
-        // Using WaitForVBlank, the whole system dies because WaitForVBlank
-        // only works if it's run on the same thread as the Present();
-        HRESULT hr = DwmFlush();
+        HRESULT hr = E_FAIL;
+        if (StaticPrefs::gfx_vsync_use_waitforvblank()) {
+          UpdateVBlankOutput();
+          if (mWaitVBlankOutput) {
+            hr = mWaitVBlankOutput->WaitForVBlank();
+          }
+        }
+        if (!SUCCEEDED(hr)) {
+          hr = DwmFlush();
+        }
         if (!SUCCEEDED(hr)) {
           // DWMFlush isn't working, fallback to software vsync.
           ScheduleSoftwareVsync(TimeStamp::Now());
@@ -1846,11 +1854,35 @@ class D3DVsyncSource final : public VsyncSource {
       return mVsyncThread->thread_id() == PlatformThread::CurrentId();
     }
 
+    void UpdateVBlankOutput() {
+      HMONITOR primary_monitor =
+          MonitorFromWindow(nullptr, MONITOR_DEFAULTTOPRIMARY);
+      if (primary_monitor == mWaitVBlankMonitor && mWaitVBlankOutput) {
+        return;
+      }
+
+      mWaitVBlankMonitor = primary_monitor;
+
+      RefPtr<IDXGIOutput> output = nullptr;
+      if (DeviceManagerDx* dx = DeviceManagerDx::Get()) {
+        if (dx->GetOutputFromMonitor(mWaitVBlankMonitor, &output)) {
+          mWaitVBlankOutput = output;
+          return;
+        }
+      }
+
+      // failed to convert a monitor to an output so keep trying
+      mWaitVBlankOutput = nullptr;
+    }
+
     TimeStamp mPrevVsync;
     Monitor mVsyncEnabledLock;
     base::Thread* mVsyncThread;
     TimeDuration mVsyncRate;
     bool mVsyncEnabled;
+
+    HMONITOR mWaitVBlankMonitor;
+    RefPtr<IDXGIOutput> mWaitVBlankOutput;
   };  // end d3dvsyncdisplay
 
   D3DVsyncSource() { mPrimaryDisplay = new D3DVsyncDisplay(); }

modules/libpref/init/StaticPrefList.yaml

@@ -3989,6 +3989,11 @@
   value: 10
   mirror: once
 
+- name: gfx.vsync.use-waitforvblank
+  type: RelaxedAtomicBool
+  value: false
+  mirror: always
+
 # We expose two prefs: gfx.webrender.all and gfx.webrender.enabled.
 # The first enables WR+additional features, and the second just enables WR.
 # For developer convenience, building with --enable-webrender=true or just