blob: 01b4e4db142f0498a3568b7702399e3ede0fe70f [file] [log] [blame]
* Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
#include <assert.h>
#include <memory>
#include "webrtc/modules/desktop_capture/desktop_capturer.h"
#include "webrtc/modules/desktop_capture/desktop_frame_win.h"
#include "webrtc/modules/desktop_capture/window_finder_win.h"
#include "webrtc/modules/desktop_capture/win/screen_capture_utils.h"
#include "webrtc/modules/desktop_capture/win/window_capture_utils.h"
#include "webrtc/rtc_base/checks.h"
#include "webrtc/rtc_base/constructormagic.h"
#include "webrtc/rtc_base/logging.h"
#include "webrtc/rtc_base/win32.h"
namespace webrtc {
namespace {
BOOL CALLBACK WindowsEnumerationHandler(HWND hwnd, LPARAM param) {
DesktopCapturer::SourceList* list =
// Skip windows that are invisible, minimized, have no title, or are owned,
// unless they have the app window style set.
int len = GetWindowTextLength(hwnd);
HWND owner = GetWindow(hwnd, GW_OWNER);
LONG exstyle = GetWindowLong(hwnd, GWL_EXSTYLE);
if (len == 0 || IsIconic(hwnd) || !IsWindowVisible(hwnd) ||
(owner && !(exstyle & WS_EX_APPWINDOW))) {
return TRUE;
// Skip the Program Manager window and the Start button.
const size_t kClassLength = 256;
WCHAR class_name[kClassLength];
const int class_name_length = GetClassName(hwnd, class_name, kClassLength);
<< "Error retrieving the application's class name";
// Skip Program Manager window and the Start button. This is the same logic
// that's used in Win32WindowPicker in libjingle. Consider filtering other
// windows as well (e.g. toolbars).
if (wcscmp(class_name, L"Progman") == 0 || wcscmp(class_name, L"Button") == 0)
return TRUE;
// Windows 8 introduced a "Modern App" identified by their class name being
// either ApplicationFrameWindow or windows.UI.Core.coreWindow. The
// associated windows cannot be captured, so we skip them.
if (rtc::IsWindows8OrLater() &&
(wcscmp(class_name, L"ApplicationFrameWindow") == 0 ||
wcscmp(class_name, L"Windows.UI.Core.CoreWindow") == 0)) {
return TRUE;
DesktopCapturer::Source window; = reinterpret_cast<WindowId>(hwnd);
const size_t kTitleLength = 500;
WCHAR window_title[kTitleLength];
// Truncate the title if it's longer than kTitleLength.
GetWindowText(hwnd, window_title, kTitleLength);
window.title = rtc::ToUtf8(window_title);
// Skip windows when we failed to convert the title or it is empty.
if (window.title.empty())
return TRUE;
return TRUE;
// Retrieves the rectangle of the window rect which is drawable by either OS or
// the owner application. The returned DesktopRect is in system coordinates.
// This function returns false if native APIs fail.
// When |window| is maximized, its borders and shadow effect will be ignored by
// OS and leave black. So we prefer to use GetCroppedWindowRect() when capturing
// its content to avoid the black area in the final DesktopFrame. But when the
// window is in normal mode, borders and shadow should be included.
bool GetWindowDrawableRect(HWND window,
DesktopRect* drawable_rect,
DesktopRect* original_rect) {
if (!GetWindowRect(window, original_rect)) {
return false;
bool is_maximized = false;
if (!IsWindowMaximized(window, &is_maximized)) {
return false;
if (is_maximized) {
return GetCroppedWindowRect(
window, drawable_rect, /* original_rect */ nullptr);
*drawable_rect = *original_rect;
return true;
class WindowCapturerWin : public DesktopCapturer {
~WindowCapturerWin() override;
// DesktopCapturer interface.
void Start(Callback* callback) override;
void CaptureFrame() override;
bool GetSourceList(SourceList* sources) override;
bool SelectSource(SourceId id) override;
bool FocusOnSelectedSource() override;
bool IsOccluded(const DesktopVector& pos) override;
Callback* callback_ = nullptr;
// HWND and HDC for the currently selected window or nullptr if window is not
// selected.
HWND window_ = nullptr;
DesktopSize previous_size_;
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_;
WindowFinderWin window_finder_;
WindowCapturerWin::WindowCapturerWin() {}
WindowCapturerWin::~WindowCapturerWin() {}
bool WindowCapturerWin::GetSourceList(SourceList* sources) {
SourceList result;
LPARAM param = reinterpret_cast<LPARAM>(&result);
// EnumWindows only enumerates root windows.
if (!EnumWindows(&WindowsEnumerationHandler, param))
return false;
std::map<HWND, DesktopSize> new_map;
for (const auto& item : *sources) {
HWND hwnd = reinterpret_cast<HWND>(;
new_map[hwnd] = window_size_map_[hwnd];
return true;
bool WindowCapturerWin::SelectSource(SourceId id) {
HWND window = reinterpret_cast<HWND>(id);
if (!IsWindow(window) || !IsWindowVisible(window) || IsIconic(window))
return false;
window_ = window;
// 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;
bool WindowCapturerWin::FocusOnSelectedSource() {
if (!window_)
return false;
if (!IsWindow(window_) || !IsWindowVisible(window_) || IsIconic(window_))
return false;
return BringWindowToTop(window_) != FALSE &&
SetForegroundWindow(window_) != FALSE;
bool WindowCapturerWin::IsOccluded(const DesktopVector& pos) {
DesktopVector sys_pos = pos.add(GetFullscreenRect().top_left());
return reinterpret_cast<HWND>(window_finder_.GetWindowUnderPoint(sys_pos))
!= window_;
void WindowCapturerWin::Start(Callback* callback) {
callback_ = callback;
void WindowCapturerWin::CaptureFrame() {
if (!window_) {
LOG(LS_ERROR) << "Window hasn't been selected: " << GetLastError();
callback_->OnCaptureResult(Result::ERROR_PERMANENT, nullptr);
// Stop capturing if the window has been closed.
if (!IsWindow(window_)) {
callback_->OnCaptureResult(Result::ERROR_PERMANENT, nullptr);
DesktopRect cropped_rect;
DesktopRect original_rect;
if (!GetWindowDrawableRect(window_, &cropped_rect, &original_rect)) {
LOG(LS_WARNING) << "Failed to get drawable window area: " << GetLastError();
callback_->OnCaptureResult(Result::ERROR_TEMPORARY, nullptr);
// Return a 1x1 black frame if the window is minimized or invisible, to match
// behavior on mace. Window can be temporarily invisible during the
// transition of full screen mode on/off.
if (original_rect.is_empty() ||
IsIconic(window_) ||
!IsWindowVisible(window_)) {
std::unique_ptr<DesktopFrame> frame(
new BasicDesktopFrame(DesktopSize(1, 1)));
memset(frame->data(), 0, frame->stride() * frame->size().height());
previous_size_ = frame->size();
window_size_map_[window_] = previous_size_;
callback_->OnCaptureResult(Result::SUCCESS, std::move(frame));
HDC window_dc = GetWindowDC(window_);
if (!window_dc) {
LOG(LS_WARNING) << "Failed to get window DC: " << GetLastError();
callback_->OnCaptureResult(Result::ERROR_TEMPORARY, nullptr);
DesktopSize window_dc_size;
if (GetDcSize(window_dc, &window_dc_size)) {
// The |window_dc_size| is used to detect the scaling of the original
// window. If the application does not support high-DPI settings, it will
// be scaled by Windows according to the scaling setting.
// So the size of the |window_dc|, i.e. the bitmap we can retrieve from
// PrintWindow() or BitBlt() function, will be smaller than
// |original_rect| and |cropped_rect|. Part of the captured desktop frame
// will be black. See
// bug for
// details.
// If |window_dc_size| is smaller than |window_rect|, let's resize both
// |original_rect| and |cropped_rect| according to the scaling factor.
const double vertical_scale =
static_cast<double>(window_dc_size.width()) / original_rect.width();
const double horizontal_scale =
static_cast<double>(window_dc_size.height()) / original_rect.height();
original_rect.Scale(vertical_scale, horizontal_scale);
cropped_rect.Scale(vertical_scale, horizontal_scale);
std::unique_ptr<DesktopFrameWin> frame(
DesktopFrameWin::Create(cropped_rect.size(), nullptr, window_dc));
if (!frame.get()) {
ReleaseDC(window_, window_dc);
callback_->OnCaptureResult(Result::ERROR_TEMPORARY, nullptr);
HDC mem_dc = CreateCompatibleDC(window_dc);
HGDIOBJ previous_object = SelectObject(mem_dc, frame->bitmap());
BOOL result = FALSE;
// When desktop composition (Aero) is enabled each window is rendered to a
// private buffer allowing BitBlt() to get the window content even if the
// window is occluded. PrintWindow() is slower but lets rendering the window
// contents to an off-screen device context when Aero is not available.
// PrintWindow() is not supported by some applications.
// If Aero is enabled, we prefer BitBlt() because it's faster and avoids
// window flickering. Otherwise, we prefer PrintWindow() because BitBlt() may
// render occluding windows on top of the desired window.
// When composition is enabled the DC returned by GetWindowDC() doesn't always
// have window frame rendered correctly. Windows renders it only once and then
// caches the result between captures. We hack it around by calling
// PrintWindow() whenever window size changes, including the first time of
// capturing - it somehow affects what we get from BitBlt() on the subsequent
// captures.
if (!aero_checker_.IsAeroEnabled() || !previous_size_.equals(frame->size())) {
result = PrintWindow(window_, mem_dc, 0);
// Aero is enabled or PrintWindow() failed, use BitBlt.
if (!result) {
result = BitBlt(mem_dc, 0, 0, frame->size().width(), frame->size().height(),
cropped_rect.left() - original_rect.left(), -,
SelectObject(mem_dc, previous_object);
ReleaseDC(window_, window_dc);
previous_size_ = frame->size();
window_size_map_[window_] = previous_size_;
if (result) {
callback_->OnCaptureResult(Result::SUCCESS, std::move(frame));
} else {
LOG(LS_ERROR) << "Both PrintWindow() and BitBlt() failed.";
callback_->OnCaptureResult(Result::ERROR_TEMPORARY, nullptr);
} // namespace
// static
std::unique_ptr<DesktopCapturer> DesktopCapturer::CreateRawWindowCapturer(
const DesktopCaptureOptions& options) {
return std::unique_ptr<DesktopCapturer>(new WindowCapturerWin());
} // namespace webrtc