linux-capture: Conditionally register PipeWire captures

Right now we just assume that every compositor and portal implementation
exposes both window and monitor captures, but that's not true, and in fact
the Desktop portal provides a simple mechanism to check which source types
are available: a D-Bus property called "AvailableSourceTypes".

Read this D-Bus property, and use it to conditionally register the desktop
and the window captures.

Related: https://github.com/obsproject/obs-studio/issues/4815

plugins/linux-capture/CMakeLists.txt

@@ -72,11 +72,13 @@ if(ENABLE_PIPEWIRE)
 		${linux-capture_SOURCES}
 		pipewire.c
 		pipewire-capture.c
+		portal.c
 	)
 	set(linux-capture_HEADERS
 		${linux-capture_HEADERS}
 		pipewire.h
 		pipewire-capture.h
+		portal.h
 	)
 	set(linux-capture_LIBRARIES
 		${linux-capture_LIBRARIES}

plugins/linux-capture/pipewire-capture.c

@@ -19,6 +19,7 @@
  */
 
 #include "pipewire.h"
+#include "portal.h"
 
 /* obs_source_info methods */
 
@@ -106,6 +107,23 @@ static void pipewire_capture_video_render(void *data, gs_effect_t *effect)
 
 void pipewire_capture_load(void)
 {
+	uint32_t available_capture_types = portal_get_available_capture_types();
+	bool desktop_capture_available =
+		(available_capture_types & DESKTOP_CAPTURE) != 0;
+	bool window_capture_available =
+		(available_capture_types & WINDOW_CAPTURE) != 0;
+
+	if (available_capture_types == 0) {
+		blog(LOG_INFO, "[pipewire] No captures available");
+		return;
+	}
+
+	blog(LOG_INFO, "[pipewire] Available captures:");
+	if (desktop_capture_available)
+		blog(LOG_INFO, "[pipewire]     - Desktop capture");
+	if (window_capture_available)
+		blog(LOG_INFO, "[pipewire]     - Window capture");
+
 	// Desktop capture
 	const struct obs_source_info pipewire_desktop_capture_info = {
 		.id = "pipewire-desktop-capture-source",
@@ -124,7 +142,8 @@ void pipewire_capture_load(void)
 		.video_render = pipewire_capture_video_render,
 		.icon_type = OBS_ICON_TYPE_DESKTOP_CAPTURE,
 	};
-	obs_register_source(&pipewire_desktop_capture_info);
+	if (desktop_capture_available)
+		obs_register_source(&pipewire_desktop_capture_info);
 
 	// Window capture
 	const struct obs_source_info pipewire_window_capture_info = {
@@ -144,7 +163,8 @@ void pipewire_capture_load(void)
 		.video_render = pipewire_capture_video_render,
 		.icon_type = OBS_ICON_TYPE_WINDOW_CAPTURE,
 	};
-	obs_register_source(&pipewire_window_capture_info);
+	if (window_capture_available)
+		obs_register_source(&pipewire_window_capture_info);
 
 	pw_init(NULL, NULL);
 }

plugins/linux-capture/portal.c

@@ -0,0 +1,74 @@
+/* portal.c
+ *
+ * Copyright 2021 Georges Basile Stavracas Neto <[email protected]>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "portal.h"
+#include "pipewire.h"
+
+static GDBusConnection *connection = NULL;
+static GDBusProxy *proxy = NULL;
+
+static void ensure_proxy(void)
+{
+	g_autoptr(GError) error = NULL;
+	if (!connection) {
+		connection = g_bus_get_sync(G_BUS_TYPE_SESSION, NULL, &error);
+
+		if (error) {
+			blog(LOG_WARNING,
+			     "[portals] Error retrieving D-Bus connection: %s",
+			     error->message);
+			return;
+		}
+	}
+
+	if (!proxy) {
+		proxy = g_dbus_proxy_new_sync(
+			connection, G_DBUS_PROXY_FLAGS_NONE, NULL,
+			"org.freedesktop.portal.Desktop",
+			"/org/freedesktop/portal/desktop",
+			"org.freedesktop.portal.ScreenCast", NULL, &error);
+
+		if (error) {
+			blog(LOG_WARNING,
+			     "[portals] Error retrieving D-Bus proxy: %s",
+			     error->message);
+			return;
+		}
+	}
+}
+
+uint32_t portal_get_available_capture_types(void)
+{
+	g_autoptr(GVariant) cached_source_types = NULL;
+	uint32_t available_source_types;
+
+	ensure_proxy();
+
+	if (!proxy)
+		return 0;
+
+	cached_source_types =
+		g_dbus_proxy_get_cached_property(proxy, "AvailableSourceTypes");
+	available_source_types =
+		cached_source_types ? g_variant_get_uint32(cached_source_types)
+				    : 0;
+
+	return available_source_types;
+}

plugins/linux-capture/portal.h

@@ -0,0 +1,25 @@
+/* portal.c
+ *
+ * Copyright 2021 Georges Basile Stavracas Neto <[email protected]>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+uint32_t portal_get_available_capture_types(void);