fix: use generic capturer to list both screens and windows when possible

Screensharing with PipeWire via XDG Desktop Portal requires explicit
user permission via permission dialogs. Chromium has separate tabs for
screens and windows and thus its portal implementation requests
permissions separately for each. However, the screencast portal has no
such limitation and supports both screens and windows in a single
request.

Support for this has been implemented in WebRTC by adding a new method
called `CreateGenericCapturer`. This has been backported here and the
`desktopCapturer` implementation has been modified to use it.
Additionally, Chromium has been patched to use same generic capturer to
ensure that the source IDs remain valid for `getUserMedia`.

patches/chromium/.patches

@@ -131,3 +131,4 @@ fix_select_the_first_menu_item_when_opened_via_keyboard.patch
 fix_return_v8_value_from_localframe_requestexecutescript.patch
 fix_harden_blink_scriptstate_maybefrom.patch
 chore_add_buildflag_guard_around_new_include.patch
+fix_use_delegated_generic_capturer_when_available.patch

patches/chromium/fix_use_delegated_generic_capturer_when_available.patch

@@ -0,0 +1,54 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Athul Iddya <athul@iddya.com>
+Date: Fri, 14 Jul 2023 08:03:37 -0700
+Subject: fix: use delegated generic capturer when available
+
+When the generic capturer is used to fetch capture sources, the returned
+ID will be arbitrarily prefixed with "screen" or "window" regardless of
+the source type. If the window capturer is used to stream video when the
+source was a screen or vice-versa, the stream fails to restart in
+delegated capturers like PipeWire.
+
+To fix this, use the generic capturer to fetch the media stream if it's
+delegated and available. This does not cause any issues if the original
+capturer was window or screen-specific, as the IDs remain valid for
+generic capturer as well.
+
+diff --git a/content/browser/media/capture/desktop_capture_device.cc b/content/browser/media/capture/desktop_capture_device.cc
+index b0c4efdd8a6401e09520bdfa96221e5addcfd829..f5b7447938f70dd4623a60fa6a856775b627f3d6 100644
+--- a/content/browser/media/capture/desktop_capture_device.cc
++++ b/content/browser/media/capture/desktop_capture_device.cc
+@@ -794,8 +794,14 @@ std::unique_ptr<media::VideoCaptureDevice> DesktopCaptureDevice::Create(
+               DesktopCapturerLacros::CaptureType::kScreen,
+               webrtc::DesktopCaptureOptions());
+ #else
+-      std::unique_ptr<webrtc::DesktopCapturer> screen_capturer(
+-          webrtc::DesktopCapturer::CreateScreenCapturer(options));
++      std::unique_ptr<webrtc::DesktopCapturer> screen_capturer;
++      if (auto generic_capturer =
++              webrtc::DesktopCapturer::CreateGenericCapturer(options);
++          generic_capturer && generic_capturer->GetDelegatedSourceListController()) {
++        screen_capturer = std::move(generic_capturer);
++      } else {
++        screen_capturer = webrtc::DesktopCapturer::CreateScreenCapturer(options);
++      }
+ #endif
+       if (screen_capturer && screen_capturer->SelectSource(source.id)) {
+         capturer = std::make_unique<webrtc::DesktopAndCursorComposer>(
+@@ -814,8 +820,14 @@ std::unique_ptr<media::VideoCaptureDevice> DesktopCaptureDevice::Create(
+           new DesktopCapturerLacros(DesktopCapturerLacros::CaptureType::kWindow,
+                                     webrtc::DesktopCaptureOptions()));
+ #else
+-      std::unique_ptr<webrtc::DesktopCapturer> window_capturer =
+-          webrtc::DesktopCapturer::CreateWindowCapturer(options);
++      std::unique_ptr<webrtc::DesktopCapturer> window_capturer;
++      if (auto generic_capturer =
++              webrtc::DesktopCapturer::CreateGenericCapturer(options);
++          generic_capturer && generic_capturer->GetDelegatedSourceListController()) {
++        window_capturer = std::move(generic_capturer);
++      } else {
++        window_capturer = webrtc::DesktopCapturer::CreateWindowCapturer(options);
++      }
+ #endif
+       if (window_capturer && window_capturer->SelectSource(source.id)) {
+         capturer = std::make_unique<webrtc::DesktopAndCursorComposer>(

shell/browser/api/electron_api_desktop_capturer.cc

@@ -234,6 +234,33 @@ void DesktopCapturer::StartHandling(bool capture_window,
   // clear any existing captured sources.
   captured_sources_.clear();
 
+  if (capture_window && capture_screen) {
+    // Some capturers like PipeWire suppport a single capturer for both screens
+    // and windows. Use it if possible, treating both as window capture
+    if (auto capturer = webrtc::DesktopCapturer::CreateGenericCapturer(
+            content::desktop_capture::CreateDesktopCaptureOptions());
+        capturer && capturer->GetDelegatedSourceListController()) {
+      capture_screen_ = false;
+      capture_window_ = capture_window;
+      window_capturer_ = std::make_unique<NativeDesktopMediaList>(
+          DesktopMediaList::Type::kWindow, std::move(capturer));
+      window_capturer_->SetThumbnailSize(thumbnail_size);
+
+      OnceCallback update_callback = base::BindOnce(
+          &DesktopCapturer::UpdateSourcesList, weak_ptr_factory_.GetWeakPtr(),
+          window_capturer_.get());
+      OnceCallback failure_callback = base::BindOnce(
+          &DesktopCapturer::HandleFailure, weak_ptr_factory_.GetWeakPtr());
+
+      window_listener_ = std::make_unique<DesktopListListener>(
+          std::move(update_callback), std::move(failure_callback),
+          thumbnail_size.IsEmpty());
+      window_capturer_->StartUpdating(window_listener_.get());
+
+      return;
+    }
+  }
+
   // Start listening for captured sources.
   capture_window_ = capture_window;
   capture_screen_ = capture_screen;