blob: 1df858ca02180527ab690603bd3aeca49aae1893 [file] [log] [blame]
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "remoting/host/desktop_resizer.h"
#include <string.h>
#include <X11/extensions/Xrandr.h>
#include <X11/Xlib.h>
#include "base/command_line.h"
#include "remoting/base/logging.h"
#include "remoting/host/linux/x11_util.h"
// On Linux, we use the xrandr extension to change the desktop resolution. For
// now, we only support resize-to-client for Xvfb-based servers that can match
// the client resolution exactly. To support best-resolution matching, it would
// be necessary to implement |GetSupportedResolutions|, but it's not considered
// a priority now.
// Xrandr has a number of restrictions that make this code more complex:
// 1. It's not possible to change the resolution of an existing mode. Instead,
// the mode must be deleted and recreated.
// 2. It's not possible to delete a mode that's in use.
// 3. Errors are communicated via Xlib's spectacularly unhelpful mechanism
// of terminating the process unless you install an error handler.
// The basic approach is as follows:
// 1. Create a new mode with the correct resolution;
// 2. Switch to the new mode;
// 3. Delete the old mode.
// Since the new mode must have a different name, and we want the current mode
// name to be consistent, we then additionally:
// 4. Recreate the old mode at the new resolution;
// 5. Switch to the old mode;
// 6. Delete the temporary mode.
// Name consistency will allow a future CL to disable resize-to-client if the
// user has changed the mode to something other than "Chrome Remote Desktop
// client resolution". It doesn't make the code significantly more complex.
namespace {
int PixelsToMillimeters(int pixels, int dpi) {
DCHECK(dpi != 0);
const double kMillimetersPerInch = 25.4;
// (pixels / dpi) is the length in inches. Multiplying by
// kMillimetersPerInch converts to mm. Multiplication is done first to
// avoid integer division.
return static_cast<int>(kMillimetersPerInch * pixels / dpi);
// TODO(jamiewalch): Use the correct DPI for the mode:
const int kDefaultDPI = 96;
} // namespace
namespace remoting {
// Wrapper class for the XRRScreenResources struct.
class ScreenResources {
ScreenResources() : resources_(nullptr) {
~ScreenResources() {
bool Refresh(Display* display, Window window) {
resources_ = XRRGetScreenResources(display, window);
return resources_ != nullptr;
void Release() {
if (resources_) {
resources_ = nullptr;
RRMode GetIdForMode(const char* name) {
for (int i = 0; i < resources_->nmode; ++i) {
const XRRModeInfo& mode = resources_->modes[i];
if (strcmp(, name) == 0) {
return 0;
// For now, assume we're only ever interested in the first output.
RROutput GetOutput() {
return resources_->outputs[0];
// For now, assume we're only ever interested in the first crtc.
RRCrtc GetCrtc() {
return resources_->crtcs[0];
XRROutputInfo* GetOutputInfo(Display* display, RROutput output_id) {
return XRRGetOutputInfo(display, resources_, output_id);
XRRScreenResources* get() { return resources_; }
XRRScreenResources* resources_;
class DesktopResizerX11 : public DesktopResizer {
~DesktopResizerX11() override;
// DesktopResizer interface
ScreenResolution GetCurrentResolution() override;
std::list<ScreenResolution> GetSupportedResolutions(
const ScreenResolution& preferred) override;
void SetResolution(const ScreenResolution& resolution) override;
void RestoreResolution(const ScreenResolution& original) override;
// Create a mode, and attach it to the primary output. If the mode already
// exists, it is left unchanged.
void CreateMode(const char* name, int width, int height);
// Remove the specified mode from the primary output, and delete it. If the
// mode is in use, it is not deleted.
void DeleteMode(const char* name);
// Switch the primary output to the specified mode. If name is nullptr, the
// primary output is disabled instead, which is required before changing
// its resolution.
void SwitchToMode(const char* name);
Display* display_;
int screen_;
Window root_;
ScreenResources resources_;
bool exact_resize_;
: display_(XOpenDisplay(nullptr)),
root_(RootWindow(display_, screen_)),
HasSwitch("server-supports-exact-resize")) {
XRRSelectInput(display_, root_, RRScreenChangeNotifyMask);
DesktopResizerX11::~DesktopResizerX11() {
ScreenResolution DesktopResizerX11::GetCurrentResolution() {
if (!exact_resize_) {
// TODO(jamiewalch): Remove this early return if we decide to support
// non-Xvfb servers.
return ScreenResolution();
// TODO(lambroslambrou): Xrandr requires that we process RRScreenChangeNotify
// events, otherwise DisplayWidth and DisplayHeight do not return the current
// values. Normally, this would be done via a central X event loop, but we
// don't have one, hence this horrible hack.
// Note that the WatchFileDescriptor approach taken in XServerClipboard
// doesn't work here because resize events have already been read from the
// X server socket by the time the resize function returns, hence the
// file descriptor is never seen as readable.
while (XEventsQueued(display_, QueuedAlready)) {
XEvent event;
XNextEvent(display_, &event);
ScreenResolution result(
DisplayWidth(display_, DefaultScreen(display_)),
DisplayHeight(display_, DefaultScreen(display_))),
webrtc::DesktopVector(kDefaultDPI, kDefaultDPI));
return result;
std::list<ScreenResolution> DesktopResizerX11::GetSupportedResolutions(
const ScreenResolution& preferred) {
std::list<ScreenResolution> result;
if (exact_resize_) {
// Clamp the specified size to something valid for the X server.
int min_width = 0, min_height = 0, max_width = 0, max_height = 0;
XRRGetScreenSizeRange(display_, root_,
&min_width, &min_height,
&max_width, &max_height);
int width = std::min(std::max(preferred.dimensions().width(), min_width),
int height = std::min(std::max(preferred.dimensions().height(), min_height),
// Additionally impose a minimum size of 640x480, since anything smaller
// doesn't seem very useful.
ScreenResolution actual(
webrtc::DesktopSize(std::max(640, width), std::max(480, height)),
webrtc::DesktopVector(kDefaultDPI, kDefaultDPI));
} else {
// TODO(jamiewalch): Return the list of supported resolutions if we can't
// support exact-size matching.
return result;
void DesktopResizerX11::SetResolution(const ScreenResolution& resolution) {
if (!exact_resize_) {
// TODO(jamiewalch): Remove this early return if we decide to support
// non-Xvfb servers.
// Ignore X errors encountered while resizing the display. We might hit an
// error, for example if xrandr has been used to add a mode with the same
// name as our temporary mode, or to remove the "client resolution" mode. We
// don't want to terminate the process if this happens.
ScopedXErrorHandler handler(ScopedXErrorHandler::Ignore());
// Grab the X server while we're changing the display resolution. This ensures
// that the display configuration doesn't change under our feet.
ScopedXGrabServer grabber(display_);
// The name of the mode representing the current client view resolution and
// the temporary mode used for the reasons described at the top of this file.
// The former should be localized if it's user-visible; the latter only
// exists briefly and does not need to localized.
const char* kModeName = "Chrome Remote Desktop client resolution";
const char* kTempModeName = "Chrome Remote Desktop temporary mode";
// Actually do the resize operation, preserving the current mode name. Note
// that we have to detach the output from any mode in order to resize it
// (strictly speaking, this is only required when reducing the size, but it
// seems safe to do it regardless).
HOST_LOG << "Changing desktop size to " << resolution.dimensions().width()
<< "x" << resolution.dimensions().height();
// TODO(lambroslambrou): Use the DPI from client size information.
int width_mm = PixelsToMillimeters(resolution.dimensions().width(),
int height_mm = PixelsToMillimeters(resolution.dimensions().height(),
CreateMode(kTempModeName, resolution.dimensions().width(),
XRRSetScreenSize(display_, root_, resolution.dimensions().width(),
resolution.dimensions().height(), width_mm, height_mm);
CreateMode(kModeName, resolution.dimensions().width(),
void DesktopResizerX11::RestoreResolution(const ScreenResolution& original) {
// Since the desktop is only visible via a remote connection, the original
// resolution of the desktop will never been seen and there's no point
// restoring it; if we did, we'd just risk messing up the user's window
// layout.
void DesktopResizerX11::CreateMode(const char* name, int width, int height) {
XRRModeInfo mode;
memset(&mode, 0, sizeof(mode));
mode.width = width;
mode.height = height; = const_cast<char*>(name);
mode.nameLength = strlen(name);
XRRCreateMode(display_, root_, &mode);
if (!resources_.Refresh(display_, root_)) {
RRMode mode_id = resources_.GetIdForMode(name);
if (!mode_id) {
XRRAddOutputMode(display_, resources_.GetOutput(), mode_id);
void DesktopResizerX11::DeleteMode(const char* name) {
RRMode mode_id = resources_.GetIdForMode(name);
if (mode_id) {
XRRDeleteOutputMode(display_, resources_.GetOutput(), mode_id);
XRRDestroyMode(display_, mode_id);
resources_.Refresh(display_, root_);
void DesktopResizerX11::SwitchToMode(const char* name) {
RRMode mode_id = None;
RROutput* outputs = nullptr;
int number_of_outputs = 0;
if (name) {
mode_id = resources_.GetIdForMode(name);
outputs = resources_.get()->outputs;
number_of_outputs = resources_.get()->noutput;
XRRSetCrtcConfig(display_, resources_.get(), resources_.GetCrtc(),
CurrentTime, 0, 0, mode_id, 1, outputs, number_of_outputs);
scoped_ptr<DesktopResizer> DesktopResizer::Create() {
return make_scoped_ptr(new DesktopResizerX11);
} // namespace remoting