draw_bmp: add a function to return a single-texture OSD overlay

Maybe this is useful for some of the lesser VOs. It's preferable over
bad ad-hoc solutions based on the more complex sub_bitmap data
structures (as observed e.g. in vo_vaapi.c), and does not use that much
more code since draw_bmp already created such an overlay internally.

But I still wanted something that avoids having to upload/render a full
screen-sized overlay if for example there's only a tiny subtitle line on
the bottom of the screen. So the new API can return a list of modified
pixels (for upload) and non-transparent pixels (for display). The way
these pixel rectangles are computed is a bit dumb and returns dumb
results, but it should be usable, and the implementation can change.

1 files changed, 42 insertions, 1 deletions

diff --git a/sub/draw_bmp.h b/sub/draw_bmp.h
index 6833d42cf7..d54a1c7685 100644
--- a/sub/draw_bmp.h
+++ b/sub/draw_bmp.h
@@ -3,12 +3,53 @@
 
 #include "osd.h"
 
+struct mp_rect;
 struct mp_image;
 struct mp_draw_sub_cache;
-bool mp_draw_sub_bitmaps(struct mp_draw_sub_cache **cache, struct mp_image *dst,
+
+struct mp_draw_sub_cache *mp_draw_sub_alloc(void *ta_parent);
+
+// Render the sub-bitmaps in sbs_list to dst. sbs_list must have been rendered
+// for an OSD resolution equivalent to dst's size (UB if not).
+// Warning: if dst is a format with alpha, and dst is not set to MP_ALPHA_PREMUL
+//          (not done by default), this will be extremely slow.
+// Warning: the caller is responsible for ensuring that dst is writable.
+//  cache: allocated instance; caches non-changing OSD parts etc.
+//  dst: image to draw to
+//  sbs_list: source sub-bitmaps
+//  returns: success
+bool mp_draw_sub_bitmaps(struct mp_draw_sub_cache *cache, struct mp_image *dst,
                          struct sub_bitmap_list *sbs_list);
+
 char *mp_draw_sub_get_dbg_info(struct mp_draw_sub_cache *c);
 
+// Return a RGBA overlay with subtitles. The returned image uses IMGFMT_BGRA and
+// premultiplied alpha, and the size specified by sbs_list.w/h.
+// This can return a list of active (act_) and modified (mod_) rectangles.
+// Active rectangles are regions that contain visible OSD pixels. Modified
+// rectangles are regions that were changed since the last call. This function
+// always makes the act region a subset of the mod region. Rectangles within a
+// list never overlap with rectangles within the same list.
+// If the user-provided lists are too small (max_*_rcs too small), multiple
+// rectangles are merged until they fit in the list.
+// You can pass max_act_rcs=0, which implies you render the whole overlay.
+//  cache: allocated instance; keeps track of changed regions
+//  sbs_list: source sub-bitmaps
+//  act_rcs: caller allocated list of non-transparent rectangles
+//  max_act_rcs: number of allocated items in act_rcs
+//  num_act_rcs: set to the number of valid items in act_rcs
+//  mod_rcs, max_mod_rcs, num_mod_rcs: modified rectangles
+//  returns: internal OSD overlay owned by cache, NULL on error
+//           read only, valid until the next call on cache
+struct mp_image *mp_draw_sub_overlay(struct mp_draw_sub_cache *cache,
+                                     struct sub_bitmap_list *sbs_list,
+                                     struct mp_rect *act_rcs,
+                                     int max_act_rcs,
+                                     int *num_act_rcs,
+                                     struct mp_rect *mod_rcs,
+                                     int max_mod_rcs,
+                                     int *num_mod_rcs);
+
 extern const bool mp_draw_sub_formats[SUBBITMAP_COUNT];
 
 #endif /* MPLAYER_DRAW_BMP_H */