From 77f3e0da5a2ad50dab6c1ebad490dad8a88a779a Mon Sep 17 00:00:00 2001
From: gyzhou <gyzhou@chromium.org>
Date: Tue, 23 Feb 2016 08:57:45 -0800
Subject: [PATCH] Screen was flickering when the picker for desktop medias
 showed up in Windows platform. Keeping track of window size for each window
 so that BitBlt() instead of PrintWindow() will be called for windows with
 unchanged sizes.

BUG=472857

Review URL: https://codereview.webrtc.org/1705183002

Cr-Commit-Position: refs/heads/master@{#11721}
---
 .../desktop_capture/window_capturer_win.cc     | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/webrtc/modules/desktop_capture/window_capturer_win.cc b/webrtc/modules/desktop_capture/window_capturer_win.cc
index 54b2768aa8..9f0ca409de 100644
--- a/webrtc/modules/desktop_capture/window_capturer_win.cc
+++ b/webrtc/modules/desktop_capture/window_capturer_win.cc
@@ -103,6 +103,10 @@ class WindowCapturerWin : public WindowCapturer {
 
   AeroChecker aero_checker_;
 
+  // This map is used to avoid flickering for the case when SelectWindow() calls
+  // are interleaved with Capture() calls.
+  std::map<HWND, DesktopSize> window_size_map_;
+
   RTC_DISALLOW_COPY_AND_ASSIGN(WindowCapturerWin);
 };
 
@@ -120,6 +124,14 @@ bool WindowCapturerWin::GetWindowList(WindowList* windows) {
   if (!EnumWindows(&WindowsEnumerationHandler, param))
     return false;
   windows->swap(result);
+
+  std::map<HWND, DesktopSize> new_map;
+  for (const auto& item : *windows) {
+    HWND hwnd = reinterpret_cast<HWND>(item.id);
+    new_map[hwnd] = window_size_map_[hwnd];
+  }
+  window_size_map_.swap(new_map);
+
   return true;
 }
 
@@ -128,7 +140,9 @@ bool WindowCapturerWin::SelectWindow(WindowId id) {
   if (!IsWindow(window) || !IsWindowVisible(window) || IsIconic(window))
     return false;
   window_ = window;
-  previous_size_.set(0, 0);
+  // When a window is not in the map, window_size_map_[window] will create an
+  // item with DesktopSize (0, 0).
+  previous_size_ = window_size_map_[window];
   return true;
 }
 
@@ -170,6 +184,7 @@ void WindowCapturerWin::Capture(const DesktopRegion& region) {
     memset(frame->data(), 0, frame->stride() * frame->size().height());
 
     previous_size_ = frame->size();
+    window_size_map_[window_] = previous_size_;
     callback_->OnCaptureCompleted(frame);
     return;
   }
@@ -236,6 +251,7 @@ void WindowCapturerWin::Capture(const DesktopRegion& region) {
   ReleaseDC(window_, window_dc);
 
   previous_size_ = frame->size();
+  window_size_map_[window_] = previous_size_;
 
   frame->mutable_updated_region()->SetRect(
       DesktopRect::MakeSize(frame->size()));