Screen sharing from Pidgin

[David Woodhouse]

On Sat, 2018-04-14 at 22:14 +0200, David Woodhouse wrote:
> I'm working on screen sharing. It's just another video screen, but the
> GStreamer src element is (in my case) ximagesrc instead v4l2src.
> 
> I suspect the best way to handle it is to define a new media type
> PURPLE_MEDIA_SEND_SCREEN. It's then left to the UI (e.g. Pidgin) to
> register an appropriate src element according to the windowing system
> in use (be it X11, Wayland, Windows, OSX, etc.), and to handle advanced
> things like choosing whether to share the whole display, or just one
> monitor, or just one window.

After looking at this a bit, I have revised the plan. In create_src()
in libpurple/media/backend-fs2.c we end up converting the media type to
and from FsMediaType, so it would need a FS_MEDIA_TYPE_SCREEN too, and
as far as FarStream is concerned is really *is* just video.

Also, that function is currently called synchronously and is expected
to immediately return the correct src element. Interacting with the
user to ask which screen/window would be slightly non-trivial.

Looks like a better option is to create the specific src element in
advance, just before creating the media stream. Then the libpurple side
becomes *really* simple...

diff --git a/libpurple/media/enum-types.h b/libpurple/media/enum-types.h
index f61d66c..9f35222 100644
--- a/libpurple/media/enum-types.h
+++ b/libpurple/media/enum-types.h
@@ -99,7 +99,11 @@ typedef enum {
        PURPLE_MEDIA_AUDIO = PURPLE_MEDIA_RECV_AUDIO | PURPLE_MEDIA_SEND_AUDIO,
        PURPLE_MEDIA_VIDEO = PURPLE_MEDIA_RECV_VIDEO | PURPLE_MEDIA_SEND_VIDEO,
        PURPLE_MEDIA_APPLICATION = PURPLE_MEDIA_RECV_APPLICATION |
-                                   PURPLE_MEDIA_SEND_APPLICATION
+                                   PURPLE_MEDIA_SEND_APPLICATION,
+       PURPLE_MEDIA_SEND = PURPLE_MEDIA_SEND_AUDIO | PURPLE_MEDIA_SEND_VIDEO |
+                           PURPLE_MEDIA_SEND_APPLICATION,
+       PURPLE_MEDIA_RECV = PURPLE_MEDIA_RECV_AUDIO | PURPLE_MEDIA_RECV_VIDEO |
+                           PURPLE_MEDIA_RECV_APPLICATION
 } PurpleMediaSessionType;
 
 /** Media state-changed types */
diff --git a/libpurple/mediamanager.c b/libpurple/mediamanager.c
index 49bb9dc..605b7dc 100644
--- a/libpurple/mediamanager.c
+++ b/libpurple/mediamanager.c
@@ -1191,6 +1191,12 @@ purple_media_manager_get_element(PurpleMediaManager *manager,
        PurpleMediaElementInfo *info = NULL;
        PurpleMediaElementType element_type;
 
+       if (type & PURPLE_MEDIA_SEND)
+               info = g_object_get_data(G_OBJECT(media), "src-element");
+       else
+               info = g_object_get_data(G_OBJECT(media), "sink-element");
+
+       if (info == NULL) {
                if (type & PURPLE_MEDIA_SEND_AUDIO)
                        info = manager->priv->audio_src;
                else if (type & PURPLE_MEDIA_RECV_AUDIO)
@@ -1203,6 +1209,7 @@ purple_media_manager_get_element(PurpleMediaManager *manager,
                        info = get_send_application_element_info ();
                else if (type & PURPLE_MEDIA_RECV_APPLICATION)
                        info = get_recv_application_element_info ();
+       }
 
        if (info == NULL)
                return NULL;

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