WIP: fix(linux/xdgportal): Expose pipewire streams as separate displays for multi monitor support

This will allow for multi-monitor support with client-side switching
using existing shortcuts (CTRL+ALT+SHIFT+Fxx) if multiple pipewire
streams are made available by the screencast portal (utilizing the
multiple option). Used in conjuction with the remotedesktop portal this
will provide easy access to all screens (at least on KDE) as one stream
per logical screen is available.

Author: Kishi85

src/platform/linux/portalgrab.cpp

@@ -172,6 +172,12 @@ namespace portal {
     int n_modifiers;
   };
 
+  struct pipewire_screenstream_t {
+    int pipewire_node;
+    int width;
+    int height;
+  };
+
   class dbus_t {
   public:
     ~dbus_t() noexcept {
@@ -281,7 +287,7 @@ namespace portal {
         return -1;
       }
 
-      if (start_portal_session(loop, session_path, pipewire_node, width, height, use_screencast_only) < 0) {
+      if (start_portal_session(loop, session_path, pipewire_streams, use_screencast_only) < 0) {
         return -1;
       }
 
@@ -331,10 +337,8 @@ namespace portal {
       return 0;
     }
 
+    std::vector<pipewire_screenstream_t> pipewire_streams;
     int pipewire_fd;
-    int pipewire_node;
-    int width;
-    int height;
 
   private:
     GDBusConnection *conn;
@@ -472,6 +476,7 @@ namespace portal {
       g_variant_builder_add(&builder, "{sv}", "handle_token", g_variant_new_string(request_token));
       g_variant_builder_add(&builder, "{sv}", "types", g_variant_new_uint32(SOURCE_TYPE_MONITOR));
       g_variant_builder_add(&builder, "{sv}", "cursor_mode", g_variant_new_uint32(CURSOR_MODE_EMBEDDED));
+      g_variant_builder_add(&builder, "{sv}", "multiple", g_variant_new_boolean(TRUE));
       if (persist) {
         g_variant_builder_add(&builder, "{sv}", "persist_mode", g_variant_new_uint32(PERSIST_UNTIL_REVOKED));
         if (!restore_token_t::empty()) {
@@ -510,7 +515,7 @@ namespace portal {
       return 0;
     }
 
-    int start_portal_session(GMainLoop *loop, const gchar *session_path, int &out_pipewire_node, int &out_width, int &out_height, bool use_screencast) {
+    int start_portal_session(GMainLoop *loop, const gchar *session_path, std::vector<pipewire_screenstream_t> &out_pipewire_streams, bool use_screencast) {
       GDBusProxy *proxy = use_screencast ? screencast_proxy : remote_desktop_proxy;
       const char *session_type = use_screencast ? "ScreenCast" : "RemoteDesktop";
 
@@ -570,10 +575,14 @@ namespace portal {
       }
 
       GVariantIter iter;
+      int out_pipewire_node;
+      int out_width;
+      int out_height;
       g_autoptr(GVariant) value = nullptr;
       g_variant_iter_init(&iter, streams);
       while (g_variant_iter_next(&iter, "(u@a{sv})", &out_pipewire_node, &value)) {
         g_variant_lookup(value, "size", "(ii)", &out_width, &out_height, nullptr);
+        out_pipewire_streams.emplace_back(pipewire_screenstream_t{out_pipewire_node, out_width, out_height});
       }
 
       return 0;
@@ -669,15 +678,13 @@ namespace portal {
      *
      * @return 0 on success, -1 on failure
      */
-    int get_or_create_session(int &pipewire_fd, int &pipewire_node, int &width, int &height) {
+    int get_or_create_session(int &pipewire_fd, std::vector<pipewire_screenstream_t> &pipewire_streams) {
       std::scoped_lock lock(mutex_);
 
       if (valid_) {
         // Return cached session data
         pipewire_fd = dup(pipewire_fd_);  // Duplicate FD for each caller
-        pipewire_node = pipewire_node_;
-        width = width_;
-        height = height_;
+        pipewire_streams = pipewire_streams_;
         BOOST_LOG(debug) << "Reusing cached portal session"sv;
         return 0;
       }
@@ -694,16 +701,12 @@ namespace portal {
 
       // Cache the session data
       pipewire_fd_ = dbus_->pipewire_fd;
-      pipewire_node_ = dbus_->pipewire_node;
-      width_ = dbus_->width;
-      height_ = dbus_->height;
+      pipewire_streams_ = dbus_->pipewire_streams;
       valid_ = true;
 
       // Return to caller (duplicate FD so each caller has their own)
       pipewire_fd = dup(pipewire_fd_);
-      pipewire_node = pipewire_node_;
-      width = width_;
-      height = height_;
+      pipewire_streams = pipewire_streams_;
 
       BOOST_LOG(debug) << "Created new portal session (cached)"sv;
       return 0;
@@ -759,9 +762,7 @@ namespace portal {
     std::mutex mutex_;
     std::unique_ptr<dbus_t> dbus_;
     int pipewire_fd_ = -1;
-    int pipewire_node_ = 0;
-    int width_ = 0;
-    int height_ = 0;
+    std::vector<pipewire_screenstream_t> pipewire_streams_;
     bool valid_ = false;
     bool maxframerate_failed_ = false;
   };
@@ -1235,13 +1236,31 @@ namespace portal {
         return -1;
       }
 
+      // Convert display name back to int as it is an index
+      int display_index = -1;
+      if (!display_name.empty()) {
+        display_index = std::stoi(display_name);
+      }
+
       // Use cached portal session to avoid creating multiple screen recordings
       int pipewire_fd = -1;
-      int pipewire_node = 0;
-      if (session_cache_t::instance().get_or_create_session(pipewire_fd, pipewire_node, width, height) < 0) {
+      std::vector<pipewire_screenstream_t> pipewire_streams;
+      if (session_cache_t::instance().get_or_create_session(pipewire_fd, pipewire_streams) < 0) {
         return -1;
       }
 
+      // If stream_index is out of the currently valid range, use the first display to stream
+      if (display_index < 0 || display_index >= pipewire_streams.size()) {
+        BOOST_LOG(warning) << "Display index out of range (using 0): "sv << display_index;
+        display_index = 0;
+      }
+
+      // Select correct stream for requested display
+      int pipewire_node = pipewire_streams[display_index].pipewire_node;
+      width = pipewire_streams[display_index].width;
+      height = pipewire_streams[display_index].height;
+      BOOST_LOG(info) << "[portalgrab] Using display "sv << display_index << " resolution: "sv << width << "x"sv << height;
+
       framerate = config.framerate;
 
       if (!shared_state) {
@@ -1641,7 +1660,18 @@ namespace platf {
 
     pw_init(nullptr, nullptr);
 
-    display_names.emplace_back("org.freedesktop.portal.Desktop");
+    // TODO: Unsure if it is better to use session cache here. Querying directly will always yield uptodate results but could fail if only one portal is allowed.
+    if (dbus->connect_to_portal() < 0) {
+      BOOST_LOG(warning) << "[portalgrab] Failed to connect to portal. Cannot enumerate displays, returning empty list.";
+      return {};
+    }
+    for (int x = 0; x < dbus->pipewire_streams.size(); ++x) {
+      auto display = dbus->pipewire_streams[x];
+      BOOST_LOG(info) << "[portalgrab] Found display "sv << x << " size: "sv << display.width << "x"sv << display.height;
+      // TODO: It might be better to use screen position+resolution here to detect changes in portal but it's a lot complexer to match later
+      display_names.emplace_back(std::to_string(x));
+    }
+    // TODO: Check if we need to close the dbus/portal connection here or not (if not using session cache)
     return display_names;
   }
 }  // namespace platf