player/video: add VOCTRL_CONTENT_TYPE

mpv's core already keeps track of whether or not it thinks a track is an
image. Some VOs (i.e. wayland) would benefit from knowing if what is
currently being displayed is an image or not so add a new VOCTRL that
signals this anytime we load a new file with a VO. Additionally, let's
add a helper enum for signaling the kind of content that is being
displayed. There is now MP_CONTENT_NONE (strictly for force window being
used on a track with no image/video), MP_CONTENT_IMAGE, and
MP_CONTENT_VIDEO. See the next commit for the actual usage of this (with
wayland).

player/core.h

@@ -556,6 +556,7 @@ double get_play_end_pts(struct MPContext *mpctx);
 double get_play_start_pts(struct MPContext *mpctx);
 bool get_ab_loop_times(struct MPContext *mpctx, double t[2]);
 void merge_playlist_files(struct playlist *pl);
+void update_content_type(struct MPContext *mpctx, struct track *track);
 void update_vo_playback_state(struct MPContext *mpctx);
 void update_window_title(struct MPContext *mpctx, bool force);
 void error_on_track(struct MPContext *mpctx, struct track *track);

player/misc.c

@@ -169,6 +169,20 @@ void issue_refresh_seek(struct MPContext *mpctx, enum seek_precision min_prec)
     queue_seek(mpctx, MPSEEK_ABSOLUTE, get_current_time(mpctx), min_prec, 0);
 }
 
+void update_content_type(struct MPContext *mpctx, struct track *track)
+{
+    enum mp_content_type content_type;
+    if (!track || !track->vo_c) {
+        content_type = MP_CONTENT_NONE;
+    } else if (track->image) {
+        content_type = MP_CONTENT_IMAGE;
+    } else {
+        content_type = MP_CONTENT_VIDEO;
+    }
+    if (mpctx->video_out)
+        vo_control(mpctx->video_out, VOCTRL_CONTENT_TYPE, (void *)content_type);
+}
+
 void update_vo_playback_state(struct MPContext *mpctx)
 {
     if (mpctx->video_out && mpctx->video_out->config_ok) {

player/playloop.c

@@ -1036,6 +1036,8 @@ int handle_force_window(struct MPContext *mpctx, bool force)
         };
         if (vo_reconfig(vo, &p) < 0)
             goto err;
+        struct track *track = mpctx->current_track[0][STREAM_VIDEO];
+        update_content_type(mpctx, track);
         update_screensaver_state(mpctx);
         vo_set_paused(vo, true);
         vo_redraw(vo);

player/video.c

@@ -276,6 +276,7 @@ void reinit_video_chain_src(struct MPContext *mpctx, struct track *track)
     if (!recreate_video_filters(mpctx))
         goto err_out;
 
+    update_content_type(mpctx, track);
     update_screensaver_state(mpctx);
 
     vo_set_paused(vo_c->vo, get_internal_paused(mpctx));

video/out/vo.h

@@ -95,6 +95,8 @@ enum mp_voctrl {
 
     VOCTRL_SET_CURSOR_VISIBILITY,       // bool*
 
+    VOCTRL_CONTENT_TYPE,                // enum mp_content_type*
+
     VOCTRL_KILL_SCREENSAVER,
     VOCTRL_RESTORE_SCREENSAVER,
 
@@ -129,6 +131,13 @@ enum mp_voctrl {
     VOCTRL_EXTERNAL_RESIZE,
 };
 
+// Helper to expose what kind of content is curently playing to the VO.
+enum mp_content_type {
+    MP_CONTENT_NONE, // used for force-window
+    MP_CONTENT_IMAGE,
+    MP_CONTENT_VIDEO,
+};
+
 #define VO_TRUE         true
 #define VO_FALSE        false
 #define VO_ERROR        -1