subs, vo: do sub bitmap change detection by comparing IDs

vo_vdpau and vo_gl cache the last subtitle bitmaps uploaded to video
card in case they stay the same over multiple frames. Detecting
whether the bitmaps have changed and should be re-uploaded was
somewhat fragile. Change the VO API to provide a bitmap ID which can
be compared with what the VO has to determine whether a new upload of
the bitmaps is needed.

Conflicts:
	libvo/vo_gl.c

Note: the changes for vo_gl.c were not merged. Instead, eosd_packer is
modified to use the new way of detecting EOSD changes. This takes care
of vo_gl, vo_gl3 and vo_direct3d, which all render EOSD. They don't
need to be updated in turn.

1 files changed, 2 insertions, 1 deletions

diff --git a/sub/sub.h b/sub/sub.h
index 8a8a2ab941..05c89af565 100644
--- a/sub/sub.h
+++ b/sub/sub.h
@@ -63,7 +63,8 @@ struct osd_state {
     struct ass_library *ass_library;
     struct ass_renderer *ass_renderer;
     struct sh_sub *sh_sub;
-    bool changed_outside_sd;
+    int bitmap_id;
+    int bitmap_pos_id;
     double sub_pts;
     double sub_offset;
     struct mp_eosd_res dim;