blob: ecc2c9653308aaaf390bb06b5a2b09a71c65344d [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 <string.h>
#include <memory>
#include <set>
#include <utility>
#include <X11/extensions/Xdamage.h>
#include <X11/extensions/Xfixes.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include "webrtc/modules/desktop_capture/desktop_capture_options.h"
#include "webrtc/modules/desktop_capture/desktop_capturer.h"
#include "webrtc/modules/desktop_capture/desktop_frame.h"
#include "webrtc/modules/desktop_capture/screen_capture_frame_queue.h"
#include "webrtc/modules/desktop_capture/screen_capturer_helper.h"
#include "webrtc/modules/desktop_capture/shared_desktop_frame.h"
#include "webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.h"
#include "webrtc/rtc_base/checks.h"
#include "webrtc/rtc_base/constructormagic.h"
#include "webrtc/rtc_base/logging.h"
#include "webrtc/rtc_base/timeutils.h"
namespace webrtc {
namespace {
// A class to perform video frame capturing for Linux.
// If XDamage is used, this class sets DesktopFrame::updated_region() according
// to the areas reported by XDamage. Otherwise this class does not detect
// DesktopFrame::updated_region(), the field is always set to the entire frame
// rectangle. ScreenCapturerDifferWrapper should be used if that functionality
// is necessary.
class ScreenCapturerLinux : public DesktopCapturer,
public SharedXDisplay::XEventHandler {
~ScreenCapturerLinux() override;
// TODO(ajwong): Do we really want this to be synchronous?
bool Init(const DesktopCaptureOptions& options);
// DesktopCapturer interface.
void Start(Callback* delegate) override;
void CaptureFrame() override;
bool GetSourceList(SourceList* sources) override;
bool SelectSource(SourceId id) override;
Display* display() { return options_.x_display()->display(); }
// SharedXDisplay::XEventHandler interface.
bool HandleXEvent(const XEvent& event) override;
void InitXDamage();
// Capture screen pixels to the current buffer in the queue. In the DAMAGE
// case, the ScreenCapturerHelper already holds the list of invalid rectangles
// from HandleXEvent(). In the non-DAMAGE case, this captures the
// whole screen, then calculates some invalid rectangles that include any
// differences between this and the previous capture.
std::unique_ptr<DesktopFrame> CaptureScreen();
// Called when the screen configuration is changed.
void ScreenConfigurationChanged();
// Synchronize the current buffer with |last_buffer_|, by copying pixels from
// the area of |last_invalid_rects|.
// Note this only works on the assumption that kNumBuffers == 2, as
// |last_invalid_rects| holds the differences from the previous buffer and
// the one prior to that (which will then be the current buffer).
void SynchronizeFrame();
void DeinitXlib();
DesktopCaptureOptions options_;
Callback* callback_ = nullptr;
// X11 graphics context.
GC gc_ = nullptr;
Window root_window_ = BadValue;
// XFixes.
bool has_xfixes_ = false;
int xfixes_event_base_ = -1;
int xfixes_error_base_ = -1;
// XDamage information.
bool use_damage_ = false;
Damage damage_handle_ = 0;
int damage_event_base_ = -1;
int damage_error_base_ = -1;
XserverRegion damage_region_ = 0;
// Access to the X Server's pixel buffer.
XServerPixelBuffer x_server_pixel_buffer_;
// A thread-safe list of invalid rectangles, and the size of the most
// recently captured screen.
ScreenCapturerHelper helper_;
// Queue of the frames buffers.
ScreenCaptureFrameQueue<SharedDesktopFrame> queue_;
// Invalid region from the previous capture. This is used to synchronize the
// current with the last buffer used.
DesktopRegion last_invalid_region_;
ScreenCapturerLinux::ScreenCapturerLinux() {
ScreenCapturerLinux::~ScreenCapturerLinux() {
options_.x_display()->RemoveEventHandler(ConfigureNotify, this);
if (use_damage_) {
damage_event_base_ + XDamageNotify, this);
bool ScreenCapturerLinux::Init(const DesktopCaptureOptions& options) {
options_ = options;
root_window_ = RootWindow(display(), DefaultScreen(display()));
if (root_window_ == BadValue) {
LOG(LS_ERROR) << "Unable to get the root window";
return false;
gc_ = XCreateGC(display(), root_window_, 0, NULL);
if (gc_ == NULL) {
LOG(LS_ERROR) << "Unable to get graphics context";
return false;
options_.x_display()->AddEventHandler(ConfigureNotify, this);
// Check for XFixes extension. This is required for cursor shape
// notifications, and for our use of XDamage.
if (XFixesQueryExtension(display(), &xfixes_event_base_,
&xfixes_error_base_)) {
has_xfixes_ = true;
} else {
LOG(LS_INFO) << "X server does not support XFixes.";
// Register for changes to the dimensions of the root window.
XSelectInput(display(), root_window_, StructureNotifyMask);
if (!x_server_pixel_buffer_.Init(display(), DefaultRootWindow(display()))) {
LOG(LS_ERROR) << "Failed to initialize pixel buffer.";
return false;
if (options_.use_update_notifications()) {
return true;
void ScreenCapturerLinux::InitXDamage() {
// Our use of XDamage requires XFixes.
if (!has_xfixes_) {
// Check for XDamage extension.
if (!XDamageQueryExtension(display(), &damage_event_base_,
&damage_error_base_)) {
LOG(LS_INFO) << "X server does not support XDamage.";
// TODO(lambroslambrou): Disable DAMAGE in situations where it is known
// to fail, such as when Desktop Effects are enabled, with graphics
// drivers (nVidia, ATI) that fail to report DAMAGE notifications
// properly.
// Request notifications every time the screen becomes damaged.
damage_handle_ = XDamageCreate(display(), root_window_,
if (!damage_handle_) {
LOG(LS_ERROR) << "Unable to initialize XDamage.";
// Create an XFixes server-side region to collate damage into.
damage_region_ = XFixesCreateRegion(display(), 0, 0);
if (!damage_region_) {
XDamageDestroy(display(), damage_handle_);
LOG(LS_ERROR) << "Unable to create XFixes region.";
damage_event_base_ + XDamageNotify, this);
use_damage_ = true;
LOG(LS_INFO) << "Using XDamage extension.";
void ScreenCapturerLinux::Start(Callback* callback) {
callback_ = callback;
void ScreenCapturerLinux::CaptureFrame() {
int64_t capture_start_time_nanos = rtc::TimeNanos();
RTC_DCHECK(!queue_.current_frame() || !queue_.current_frame()->IsShared());
// Process XEvents for XDamage and cursor shape tracking.
// ProcessPendingXEvents() may call ScreenConfigurationChanged() which
// reinitializes |x_server_pixel_buffer_|. Check if the pixel buffer is still
// in a good shape.
if (!x_server_pixel_buffer_.is_initialized()) {
// We failed to initialize pixel buffer.
callback_->OnCaptureResult(Result::ERROR_PERMANENT, nullptr);
// If the current frame is from an older generation then allocate a new one.
// Note that we can't reallocate other buffers at this point, since the caller
// may still be reading from them.
if (!queue_.current_frame()) {
new BasicDesktopFrame(x_server_pixel_buffer_.window_size()))));
std::unique_ptr<DesktopFrame> result = CaptureScreen();
if (!result) {
callback_->OnCaptureResult(Result::ERROR_TEMPORARY, nullptr);
last_invalid_region_ = result->updated_region();
result->set_capture_time_ms((rtc::TimeNanos() - capture_start_time_nanos) /
callback_->OnCaptureResult(Result::SUCCESS, std::move(result));
bool ScreenCapturerLinux::GetSourceList(SourceList* sources) {
RTC_DCHECK(sources->size() == 0);
// TODO(jiayl): implement screen enumeration.
return true;
bool ScreenCapturerLinux::SelectSource(SourceId id) {
// TODO(jiayl): implement screen selection.
return true;
bool ScreenCapturerLinux::HandleXEvent(const XEvent& event) {
if (use_damage_ && (event.type == damage_event_base_ + XDamageNotify)) {
const XDamageNotifyEvent* damage_event =
reinterpret_cast<const XDamageNotifyEvent*>(&event);
if (damage_event->damage != damage_handle_)
return false;
RTC_DCHECK(damage_event->level == XDamageReportNonEmpty);
return true;
} else if (event.type == ConfigureNotify) {
return true;
return false;
std::unique_ptr<DesktopFrame> ScreenCapturerLinux::CaptureScreen() {
std::unique_ptr<SharedDesktopFrame> frame = queue_.current_frame()->Share();
// Pass the screen size to the helper, so it can clip the invalid region if it
// expands that region to a grid.
// In the DAMAGE case, ensure the frame is up-to-date with the previous frame
// if any. If there isn't a previous frame, that means a screen-resolution
// change occurred, and |invalid_rects| will be updated to include the whole
// screen.
if (use_damage_ && queue_.previous_frame())
DesktopRegion* updated_region = frame->mutable_updated_region();
if (use_damage_ && queue_.previous_frame()) {
// Atomically fetch and clear the damage region.
XDamageSubtract(display(), damage_handle_, None, damage_region_);
int rects_num = 0;
XRectangle bounds;
XRectangle* rects = XFixesFetchRegionAndBounds(display(), damage_region_,
&rects_num, &bounds);
for (int i = 0; i < rects_num; ++i) {
rects[i].x, rects[i].y, rects[i].width, rects[i].height));
// Capture the damaged portions of the desktop.
// Clip the damaged portions to the current screen size, just in case some
// spurious XDamage notifications were received for a previous (larger)
// screen size.
for (DesktopRegion::Iterator it(*updated_region);
!it.IsAtEnd(); it.Advance()) {
if (!x_server_pixel_buffer_.CaptureRect(it.rect(), frame.get()))
return nullptr;
} else {
// Doing full-screen polling, or this is the first capture after a
// screen-resolution change. In either case, need a full-screen capture.
DesktopRect screen_rect = DesktopRect::MakeSize(frame->size());
if (!x_server_pixel_buffer_.CaptureRect(screen_rect, frame.get()))
return nullptr;
return std::move(frame);
void ScreenCapturerLinux::ScreenConfigurationChanged() {
// Make sure the frame buffers will be reallocated.
if (!x_server_pixel_buffer_.Init(display(), DefaultRootWindow(display()))) {
LOG(LS_ERROR) << "Failed to initialize pixel buffer after screen "
"configuration change.";
void ScreenCapturerLinux::SynchronizeFrame() {
// Synchronize the current buffer with the previous one since we do not
// capture the entire desktop. Note that encoder may be reading from the
// previous buffer at this time so thread access complaints are false
// positives.
// TODO(hclam): We can reduce the amount of copying here by subtracting
// |capturer_helper_|s region from |last_invalid_region_|.
DesktopFrame* current = queue_.current_frame();
DesktopFrame* last = queue_.previous_frame();
RTC_DCHECK(current != last);
for (DesktopRegion::Iterator it(last_invalid_region_);
!it.IsAtEnd(); it.Advance()) {
current->CopyPixelsFrom(*last, it.rect().top_left(), it.rect());
void ScreenCapturerLinux::DeinitXlib() {
if (gc_) {
XFreeGC(display(), gc_);
gc_ = nullptr;
if (display()) {
if (damage_handle_) {
XDamageDestroy(display(), damage_handle_);
damage_handle_ = 0;
if (damage_region_) {
XFixesDestroyRegion(display(), damage_region_);
damage_region_ = 0;
} // namespace
// static
std::unique_ptr<DesktopCapturer> DesktopCapturer::CreateRawScreenCapturer(
const DesktopCaptureOptions& options) {
if (!options.x_display())
return nullptr;
std::unique_ptr<ScreenCapturerLinux> capturer(new ScreenCapturerLinux());
if (!capturer.get()->Init(options)) {
return nullptr;
return std::move(capturer);
} // namespace webrtc