Skips the first frame in DxgiDuplicatorController

webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.cc

Index: webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.cc
diff --git a/webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.cc b/webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.cc
index 065a6148c06ba85ded23d9db3943eca650e1a306..a5f09f00407b301b112ecd7d6d2d0b62d4508564 100644
--- a/webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.cc
+++ b/webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.cc
@@ -16,8 +16,10 @@
 #include <string>
 
 #include "webrtc/base/checks.h"
+#include "webrtc/base/timeutils.h"
 #include "webrtc/modules/desktop_capture/desktop_capture_types.h"
 #include "webrtc/modules/desktop_capture/win/screen_capture_utils.h"
+#include "webrtc/system_wrappers/include/sleep.h"
 
 namespace webrtc {
 
@@ -104,14 +106,7 @@ DesktopRect DxgiDuplicatorController::ScreenRect(int id) {
 
 int DxgiDuplicatorController::ScreenCount() {
   rtc::CritScope lock(&lock_);
-  if (!Initialize()) {
-    return 0;
-  }
-  int result = 0;
-  for (auto& duplicator : duplicators_) {
-    result += duplicator.screen_count();
-  }
-  return result;
+  return ScreenCountUnlocked();
 }
 
 void DxgiDuplicatorController::Unregister(const Context* const context) {
@@ -235,7 +230,11 @@ bool DxgiDuplicatorController::DoDuplicate(Context* context,
   if (DoDuplicateUnlocked(context, monitor_id, target)) {
     return true;
   }
-  Deinitialize();
+  if (monitor_id < ScreenCountUnlocked()) {
+    // It's a user error to provide a |monitor_id| larger than screen count. We
+    // do not need to deinitialize.
+    Deinitialize();
+  }
   return false;
 }
 
@@ -256,18 +255,41 @@ bool DxgiDuplicatorController::DoDuplicateUnlocked(Context* context,
   }
 
   Setup(context);
+
+  if (!EnsureFrameCaptured(context, target)) {
+    return false;
+  }
+
+  bool result = false;
   if (monitor_id < 0) {
     // Capture entire screen.
-    for (size_t i = 0; i < duplicators_.size(); i++) {
-      if (!duplicators_[i].Duplicate(&context->contexts_[i], target)) {
-        return false;
-      }
-    }
+    result = DoDuplicateAll(context, target);
+  } else {
+    result = DoDuplicateOne(context, monitor_id, target);
+  }
+
+  if (result) {
     target->set_dpi(dpi());
     return true;
   }
 
-  // Capture one monitor.
+  return false;
+}
+
+bool DxgiDuplicatorController::DoDuplicateAll(Context* context,
+                                              SharedDesktopFrame* target) {
+  for (size_t i = 0; i < duplicators_.size(); i++) {
+    if (!duplicators_[i].Duplicate(&context->contexts_[i], target)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+bool DxgiDuplicatorController::DoDuplicateOne(Context* context,
+                                              int monitor_id,
+                                              SharedDesktopFrame* target) {
+  RTC_DCHECK(monitor_id >= 0);
   for (size_t i = 0; i < duplicators_.size() && i < context->contexts_.size();
        i++) {
     if (monitor_id >= duplicators_[i].screen_count()) {
@@ -275,15 +297,83 @@ bool DxgiDuplicatorController::DoDuplicateUnlocked(Context* context,
     } else {
       if (duplicators_[i].DuplicateMonitor(&context->contexts_[i], monitor_id,
                                            target)) {
-        target->set_dpi(dpi());
         return true;
       }
       return false;
     }
   }
-  // id >= ScreenCount(). This is a user error, so we do not need to
-  // deinitialize.
   return false;
 }
 
+int64_t DxgiDuplicatorController::GetNumFramesCaptured() const {
+  int64_t min = INT64_MAX;
+  for (const auto& duplicator : duplicators_) {
+    min = std::min(min, duplicator.GetNumFramesCaptured());
+  }
+
+  return min;
+}
+
+int DxgiDuplicatorController::ScreenCountUnlocked() {
+  if (!Initialize()) {
+    return 0;
+  }
+  int result = 0;
+  for (auto& duplicator : duplicators_) {
+    result += duplicator.screen_count();
+  }
+  return result;
+}
+
+bool DxgiDuplicatorController::EnsureFrameCaptured(Context* context,
+                                                   SharedDesktopFrame* target) {
+  // On a modern system, the FPS / monitor refresh rate is usually larger than
+  // or equal to 60. So 17 milliseconds is enough to capture at least one frame.
+  const int64_t ms_per_frame = 17;
+  // Skips the first frame to ensure a full frame refresh has happened before
+  // this function returns.
+  const int64_t frames_to_skip = 1;
+  // The total time out milliseconds for this function. If we cannot get enough
+  // frames during this time interval, this function returns false, and cause
+  // the DXGI components to be reinitialized. This usually should not happen
+  // unless the system is switching display mode when this function is being
+  // called. 500 milliseconds should be enough for ~30 frames.
+  const int64_t timeout_ms = 500;
+  if (GetNumFramesCaptured() >= frames_to_skip) {
+    return true;
+  }
+
+  std::unique_ptr<SharedDesktopFrame> fallback_frame;
+  SharedDesktopFrame* shared_frame = nullptr;
+  if (target->size().width() >= desktop_size().width() &&
+      target->size().height() >= desktop_size().height()) {
+    // |target| is large enough to cover entire screen, we do not need to use
+    // |fallback_frame|.
+    shared_frame = target;
+  } else {
+    fallback_frame = SharedDesktopFrame::Wrap(std::unique_ptr<DesktopFrame>(
+        new BasicDesktopFrame(desktop_size())));
+    shared_frame = fallback_frame.get();
+  }
+
+  const int64_t start_ms = rtc::TimeMillis();
+  int64_t last_frame_start_ms = 0;
+  while (GetNumFramesCaptured() < frames_to_skip) {
+    if (GetNumFramesCaptured() > 0) {
+      // Sleep |ms_per_frame| before capturing next frame to ensure the screen
+      // has been updated by the video adapter.
+      webrtc::SleepMs(
+          ms_per_frame - (rtc::TimeMillis() - last_frame_start_ms));
+    }
+    last_frame_start_ms = rtc::TimeMillis();
+    if (!DoDuplicateAll(context, shared_frame)) {
+      return false;
+    }
+    if (rtc::TimeMillis() - start_ms > timeout_ms) {
+      return false;
+    }
+  }
+  return true;
+}
+
 }  // namespace webrtc