[DesktopCapture] Detect screen resolution changes in DirectX capturer

webrtc/modules/desktop_capture/win/screen_capturer_win_directx.cc

Index: webrtc/modules/desktop_capture/win/screen_capturer_win_directx.cc
diff --git a/webrtc/modules/desktop_capture/win/screen_capturer_win_directx.cc b/webrtc/modules/desktop_capture/win/screen_capturer_win_directx.cc
index c30356e5753a5e454d9140106bcc223fc1fc41d5..4b789589886143c60e7e0aff00604dd86af5cae2 100644
--- a/webrtc/modules/desktop_capture/win/screen_capturer_win_directx.cc
+++ b/webrtc/modules/desktop_capture/win/screen_capturer_win_directx.cc
@@ -16,6 +16,7 @@
 #include "webrtc/base/logging.h"
 #include "webrtc/base/timeutils.h"
 #include "webrtc/modules/desktop_capture/desktop_frame.h"
+#include "webrtc/modules/desktop_capture/win/screen_capture_utils.h"
 
 namespace webrtc {
 
@@ -66,6 +67,15 @@ void ScreenCapturerWinDirectx::CaptureFrame() {
 
   int64_t capture_start_time_nanos = rtc::TimeNanos();
 
+  if (resolution_change_detector_.IsChanged(
+      GetScreenRect(kFullDesktopScreenId, L"").size())) {

[Sergey Ulanov, 2017/02/10 19:58:25]

std::wstring() for the second parameter

[Sergey Ulanov, 2017/02/10 19:58:25]

Why is it kFullDesktopScreenId instead of current_screen_id_?
There are cases when resolution of the monitor we are capturing is changed,
while total resolution of desktop stays the same.

[Sergey Ulanov, 2017/02/10 19:58:25]

indentation - this line should be indented 4 spaces more.

[Hzj_jie, 2017/02/11 01:51:22]

Done.

[Hzj_jie, 2017/02/11 01:51:22]

Done.

[Hzj_jie, 2017/02/11 01:51:22]

Three reasons,
1. it's not guaranteed GetScreenRect() returns the same size as DX APIs.
2. current_screen_id_ comes from DX APIs, which does not have a same meaning as
the parameter of GetScreenRect().
3. It's not likely the total resolution won't change if resolutions of one or
more monitors have changed. But the worst case is a temporary capture attempt,
which does not really like a big deal.

[Sergey Ulanov, 2017/02/15 01:38:52]

They maybe we should use DX API to get the screen size?
Is it possible to get displays resolutions using DX API before capturing?

[Hzj_jie, 2017/02/15 03:53:16]

Yes, technically, we can do this. But we need to initialize
DxgiDuplicatorController, which makes this issue become a cycle dependency.
Yes, we have already used DX APIs to set the resolution of frames.

[Sergey Ulanov, 2017/02/15 22:39:38]

Not sure why it's a cyclic dependency. This function should:
 1. Make sure that DxgiDuplicatorController is initialized.
 2. Get current resolution for the target screen.
 3. Verify that the resolution hasn't changed from the previous frame, and reset
frame queue if it did.
 4. Capture new frame.

If I understand correctly currently we cannot do (2) because
DxgiDuplicatorController caches screen size internally so SelectedDesktopSize()
returns out-of-date value after size changes. But I don't see any reason it
couldn't be fixed.

Anyway, I don't mind much the current approach, but at very least this code
deserves a comment to explain why it's implemented this way. Also a TODO() to
improve it.

+    // The next Duplicate() call is expected to fail. So we reset the dxgi
+    // components in-place.
+    frames_.Reset();
+    DxgiDuplicatorController::Instance()->Reset();
+    resolution_change_detector_.Reset();
+  }
+
   frames_.MoveToNextFrame();
   if (!frames_.current_frame()) {
     std::unique_ptr<DesktopFrame> new_frame;
@@ -90,6 +100,7 @@ void ScreenCapturerWinDirectx::CaptureFrame() {
             &context_, frames_.current_frame())) {
       // Screen size may be changed, so we need to reset the frames.
       frames_.Reset();
+      resolution_change_detector_.Reset();
       callback_->OnCaptureResult(Result::ERROR_TEMPORARY, nullptr);
       return;
     }
@@ -98,6 +109,7 @@ void ScreenCapturerWinDirectx::CaptureFrame() {
             &context_, current_screen_id_, frames_.current_frame())) {
       // Screen size may be changed, so we need to reset the frames.
       frames_.Reset();
+      resolution_change_detector_.Reset();
       if (current_screen_id_ >=
           DxgiDuplicatorController::Instance()->ScreenCount()) {
         // Current monitor has been removed from the system.