osd: simplify an aspect of change detection handling

There was a somewhat obscure optimization in the OSD and subtitle
rendering path: if only the position of the sub-images changed, and not
the actual image data, uploading of the image data could be skipped. In
theory, this could speed up things like scrolling subtitles.

But it turns out that even in the rare cases subtitles have such scrolls
or axis-aligned movement, modern libass rarely signals this kind of
change. Possibly this is because of sub-pixel handling and such, which
break this.

As such, it's a worthless optimization and just introduces additional
complexity and subtle bugs (especially in cases libass does the
opposite: incorrectly signaling a position change only, which happened
before). Remove this optimization, and rename bitmap_pos_id to
change_id.

13 files changed, 74 insertions, 100 deletions

diff --git a/player/command.c b/player/command.c
index 7db54d6cf8..782629500d 100644
--- a/player/command.c
+++ b/player/command.c
@@ -3931,7 +3931,7 @@ static void recreate_overlays(struct MPContext *mpctx)
     if (new == cmd->overlay_osd_current)
         new += 1; // pick the unused one
     new->format = SUBBITMAP_RGBA;
-    new->bitmap_id = new->bitmap_pos_id = 1;
+    new->change_id = 1;
     // overlay array can have unused entries, but parts list must be "packed"
     new->num_parts = 0;
     for (int n = 0; n < cmd->num_overlays; n++) {
diff --git a/sub/ass_mp.c b/sub/ass_mp.c
index 44ce330d0e..a02ff8d632 100644
--- a/sub/ass_mp.c
+++ b/sub/ass_mp.c
@@ -134,10 +134,8 @@ void mp_ass_render_frame(ASS_Renderer *renderer, ASS_Track *track, double time,
 {
     int changed;
     ASS_Image *imgs = ass_render_frame(renderer, track, time, &changed);
-    if (changed == 2)
-        res->bitmap_id = ++res->bitmap_pos_id;
-    else if (changed)
-        res->bitmap_pos_id++;
+    if (changed)
+        res->change_id++;
     res->format = SUBBITMAP_LIBASS;
 
     res->parts = *parts;
diff --git a/sub/draw_bmp.c b/sub/draw_bmp.c
index c5c0dddd29..d9cb0522df 100644
--- a/sub/draw_bmp.c
+++ b/sub/draw_bmp.c
@@ -43,7 +43,7 @@ struct sub_cache {
 };
 
 struct part {
-    int bitmap_pos_id;
+    int change_id;
     int imgfmt;
     enum mp_csp colorspace;
     enum mp_csp_levels levels;
@@ -399,7 +399,7 @@ static struct part *get_cache(struct mp_draw_sub_cache *cache,
     if (use_cache) {
         part = cache->parts[sbs->render_index];
         if (part) {
-            if (part->bitmap_pos_id != sbs->bitmap_pos_id
+            if (part->change_id != sbs->change_id
                 || part->imgfmt != format->imgfmt
                 || part->colorspace != format->params.colorspace
                 || part->levels != format->params.colorlevels)
@@ -411,7 +411,7 @@ static struct part *get_cache(struct mp_draw_sub_cache *cache,
         if (!part) {
             part = talloc(cache, struct part);
             *part = (struct part) {
-                .bitmap_pos_id = sbs->bitmap_pos_id,
+                .change_id = sbs->change_id,
                 .num_imgs = sbs->num_parts,
                 .imgfmt = format->imgfmt,
                 .levels = format->params.colorlevels,
diff --git a/sub/osd.c b/sub/osd.c
index 3e1260d3f8..7ab191191a 100644
--- a/sub/osd.c
+++ b/sub/osd.c
@@ -263,7 +263,7 @@ static void render_object(struct osd_state *osd, struct osd_object *obj,
     } else if (obj->type == OSDTYPE_EXTERNAL2) {
         if (obj->external2 && obj->external2->format) {
             *out_imgs = *obj->external2;
-            obj->external2->bitmap_id = obj->external2->bitmap_pos_id = 0;
+            obj->external2->change_id = 0;
         }
     } else if (obj->type == OSDTYPE_NAV_HIGHLIGHT) {
         if (obj->highlight_priv)
@@ -272,29 +272,23 @@ static void render_object(struct osd_state *osd, struct osd_object *obj,
         osd_object_get_bitmaps(osd, obj, out_imgs);
     }
 
-    if (obj->force_redraw) {
-        out_imgs->bitmap_id++;
-        out_imgs->bitmap_pos_id++;
-    }
+    if (obj->force_redraw)
+        out_imgs->change_id++;
 
     obj->force_redraw = false;
-    obj->vo_bitmap_id += out_imgs->bitmap_id;
-    obj->vo_bitmap_pos_id += out_imgs->bitmap_pos_id;
+    obj->vo_change_id += out_imgs->change_id;
 
     if (out_imgs->num_parts == 0)
         return;
 
-    if (obj->cached.bitmap_id == obj->vo_bitmap_id
-        && obj->cached.bitmap_pos_id == obj->vo_bitmap_pos_id
-        && formats[obj->cached.format])
+    if (obj->cached.change_id == obj->vo_change_id && formats[obj->cached.format])
     {
         *out_imgs = obj->cached;
         return;
     }
 
     out_imgs->render_index = obj->type;
-    out_imgs->bitmap_id = obj->vo_bitmap_id;
-    out_imgs->bitmap_pos_id = obj->vo_bitmap_pos_id;
+    out_imgs->change_id = obj->vo_change_id;
 
     if (formats[out_imgs->format])
         return;
diff --git a/sub/osd.h b/sub/osd.h
index a96fc63663..704a424c4c 100644
--- a/sub/osd.h
+++ b/sub/osd.h
@@ -70,8 +70,7 @@ struct sub_bitmaps {
     struct sub_bitmap *parts;
     int num_parts;
 
-    // Incremented on each change
-    int bitmap_id, bitmap_pos_id;
+    int change_id;  // Incremented on each change
 };
 
 struct mp_osd_res {
diff --git a/sub/osd_state.h b/sub/osd_state.h
index 01546d7c6f..73bfcdd7d3 100644
--- a/sub/osd_state.h
+++ b/sub/osd_state.h
@@ -36,8 +36,7 @@ struct osd_object {
     struct sub_bitmaps cached;
 
     // VO cache state
-    int vo_bitmap_id;
-    int vo_bitmap_pos_id;
+    int vo_change_id;
     struct mp_osd_res vo_res;
 
     // Internally used by osd_libass.c
diff --git a/sub/sd_lavc.c b/sub/sd_lavc.c
index 496b47459c..228690fe27 100644
--- a/sub/sd_lavc.c
+++ b/sub/sd_lavc.c
@@ -256,7 +256,7 @@ static void get_bitmaps(struct sd *sd, struct mp_osd_res d, double pts,
     res->parts = priv->outbitmaps;
     res->num_parts = current->count;
     if (priv->displayed_id != current->id)
-        res->bitmap_id = ++res->bitmap_pos_id;
+        res->change_id++;
     priv->displayed_id = current->id;
     res->format = SUBBITMAP_INDEXED;
 
diff --git a/video/out/gl_osd.c b/video/out/gl_osd.c
index 74074915a2..88a7e938fb 100644
--- a/video/out/gl_osd.c
+++ b/video/out/gl_osd.c
@@ -68,7 +68,7 @@ static const struct gl_vao_entry vertex_vao[] = {
 
 struct mpgl_osd_part {
     enum sub_bitmap_format format;
-    int bitmap_id, bitmap_pos_id;
+    int change_id;
     GLuint texture;
     int w, h;
     GLuint buffer;
@@ -278,14 +278,11 @@ static void gen_osd_cb(void *pctx, struct sub_bitmaps *imgs)
 
     struct mpgl_osd_part *osd = ctx->parts[imgs->render_index];
 
-    if (imgs->bitmap_pos_id != osd->bitmap_pos_id) {
-        if (imgs->bitmap_id != osd->bitmap_id) {
-            if (!upload_osd(ctx, osd, imgs))
-                osd->packer->count = 0;
-        }
+    if (imgs->change_id != osd->change_id) {
+        if (!upload_osd(ctx, osd, imgs))
+            osd->packer->count = 0;
 
-        osd->bitmap_id = imgs->bitmap_id;
-        osd->bitmap_pos_id = imgs->bitmap_pos_id;
+        osd->change_id = imgs->change_id;
     }
     osd->num_subparts = osd->packer->count;
 
diff --git a/video/out/vo_direct3d.c b/video/out/vo_direct3d.c
index 1977d64a11..b6e40e75ec 100644
--- a/video/out/vo_direct3d.c
+++ b/video/out/vo_direct3d.c
@@ -103,7 +103,7 @@ struct texplane {
 
 struct osdpart {
     enum sub_bitmap_format format;
-    int bitmap_id, bitmap_pos_id;
+    int change_id;
     struct d3dtex texture;
     int num_vertices;
     vertex_osd *vertices;
@@ -453,7 +453,7 @@ static void destroy_d3d_surfaces(d3d_priv *priv)
     for (int n = 0; n < MAX_OSD_PARTS; n++) {
         struct osdpart *osd = priv->osd[n];
         d3dtex_release(priv, &osd->texture);
-        osd->bitmap_id = osd->bitmap_pos_id = -1;
+        osd->change_id = -1;
     }
 
     if (priv->d3d_backbuf)
@@ -1618,14 +1618,11 @@ static struct osdpart *generate_osd(d3d_priv *priv, struct sub_bitmaps *imgs)
 
     struct osdpart *osd = priv->osd[imgs->render_index];
 
-    if (imgs->bitmap_pos_id != osd->bitmap_pos_id) {
-        if (imgs->bitmap_id != osd->bitmap_id) {
-            if (!upload_osd(priv, osd, imgs))
-                osd->packer->count = 0;
-        }
+    if (imgs->change_id != osd->change_id) {
+        if (!upload_osd(priv, osd, imgs))
+            osd->packer->count = 0;
 
-        osd->bitmap_id = imgs->bitmap_id;
-        osd->bitmap_pos_id = imgs->bitmap_pos_id;
+        osd->change_id = imgs->change_id;
         osd->num_vertices = 0;
     }
 
diff --git a/video/out/vo_sdl.c b/video/out/vo_sdl.c
index 8bde820b38..c2cc711d2f 100644
--- a/video/out/vo_sdl.c
+++ b/video/out/vo_sdl.c
@@ -177,8 +177,7 @@ struct priv {
     struct mp_osd_res osd_res;
     struct formatmap_entry osd_format;
     struct osd_bitmap_surface {
-        int bitmap_id;
-        int bitmap_pos_id;
+        int change_id;
         struct osd_target {
             SDL_Rect source;
             SDL_Rect dest;
@@ -702,7 +701,7 @@ static void generate_osd_part(struct vo *vo, struct sub_bitmaps *imgs)
     if (imgs->format == SUBBITMAP_EMPTY || imgs->num_parts == 0)
         return;
 
-    if (imgs->bitmap_pos_id == sfc->bitmap_pos_id)
+    if (imgs->change_id == sfc->change_id)
         return;
 
     if (imgs->num_parts > sfc->targets_size) {
@@ -725,49 +724,46 @@ static void generate_osd_part(struct vo *vo, struct sub_bitmaps *imgs)
             bmp->x, bmp->y, bmp->dw, bmp->dh
         };
 
-        if (imgs->bitmap_id != sfc->bitmap_id || !target->tex) {
-            // tex: alpha blended texture
-            if (target->tex) {
-                SDL_DestroyTexture(target->tex);
-                target->tex = NULL;
-            }
-            if (!target->tex)
-                target->tex = SDL_CreateTexture(vc->renderer,
-                        vc->osd_format.sdl, SDL_TEXTUREACCESS_STREAMING,
-                        bmp->w, bmp->h);
-            if (!target->tex) {
-                MP_ERR(vo, "Could not create texture\n");
-            }
-            if (target->tex) {
-                SDL_SetTextureBlendMode(target->tex,
-                                        SDL_BLENDMODE_BLEND);
-                SDL_SetTextureColorMod(target->tex, 0, 0, 0);
-                subbitmap_to_texture(vo, target->tex, bmp, 0); // RGBA -> 000A
-            }
+        // tex: alpha blended texture
+        if (target->tex) {
+            SDL_DestroyTexture(target->tex);
+            target->tex = NULL;
+        }
+        if (!target->tex)
+            target->tex = SDL_CreateTexture(vc->renderer,
+                    vc->osd_format.sdl, SDL_TEXTUREACCESS_STREAMING,
+                    bmp->w, bmp->h);
+        if (!target->tex) {
+            MP_ERR(vo, "Could not create texture\n");
+        }
+        if (target->tex) {
+            SDL_SetTextureBlendMode(target->tex,
+                                    SDL_BLENDMODE_BLEND);
+            SDL_SetTextureColorMod(target->tex, 0, 0, 0);
+            subbitmap_to_texture(vo, target->tex, bmp, 0); // RGBA -> 000A
+        }
 
-            // tex2: added texture
-            if (target->tex2) {
-                SDL_DestroyTexture(target->tex2);
-                target->tex2 = NULL;
-            }
-            if (!target->tex2)
-                target->tex2 = SDL_CreateTexture(vc->renderer,
-                        vc->osd_format.sdl, SDL_TEXTUREACCESS_STREAMING,
-                        bmp->w, bmp->h);
-            if (!target->tex2) {
-                MP_ERR(vo, "Could not create texture\n");
-            }
-            if (target->tex2) {
-                SDL_SetTextureBlendMode(target->tex2,
-                                        SDL_BLENDMODE_ADD);
-                subbitmap_to_texture(vo, target->tex2, bmp,
-                                     0xFF000000); // RGBA -> RGB1
-            }
+        // tex2: added texture
+        if (target->tex2) {
+            SDL_DestroyTexture(target->tex2);
+            target->tex2 = NULL;
+        }
+        if (!target->tex2)
+            target->tex2 = SDL_CreateTexture(vc->renderer,
+                    vc->osd_format.sdl, SDL_TEXTUREACCESS_STREAMING,
+                    bmp->w, bmp->h);
+        if (!target->tex2) {
+            MP_ERR(vo, "Could not create texture\n");
+        }
+        if (target->tex2) {
+            SDL_SetTextureBlendMode(target->tex2,
+                                    SDL_BLENDMODE_ADD);
+            subbitmap_to_texture(vo, target->tex2, bmp,
+                                    0xFF000000); // RGBA -> RGB1
         }
     }
 
-    sfc->bitmap_id = imgs->bitmap_id;
-    sfc->bitmap_pos_id = imgs->bitmap_pos_id;
+    sfc->change_id = imgs->change_id;
 }
 
 static void draw_osd_part(struct vo *vo, int index)
diff --git a/video/out/vo_vaapi.c b/video/out/vo_vaapi.c
index 8d0102be77..31479ff41b 100644
--- a/video/out/vo_vaapi.c
+++ b/video/out/vo_vaapi.c
@@ -57,7 +57,7 @@ struct vaapi_subpic {
 
 struct vaapi_osd_part {
     bool active;
-    int bitmap_pos_id;
+    int change_id;
     struct vaapi_osd_image image;
     struct vaapi_subpic subpic;
     struct osd_conv_cache *conv_cache;
@@ -345,8 +345,8 @@ static void draw_osd_cb(void *pctx, struct sub_bitmaps *imgs)
     struct priv *p = pctx;
 
     struct vaapi_osd_part *part = &p->osd_parts[imgs->render_index];
-    if (imgs->bitmap_pos_id != part->bitmap_pos_id) {
-        part->bitmap_pos_id = imgs->bitmap_pos_id;
+    if (imgs->change_id != part->change_id) {
+        part->change_id = imgs->change_id;
 
         osd_scale_rgba(part->conv_cache, imgs);
 
diff --git a/video/out/vo_vdpau.c b/video/out/vo_vdpau.c
index 89bbb142a3..995b579ba6 100644
--- a/video/out/vo_vdpau.c
+++ b/video/out/vo_vdpau.c
@@ -136,8 +136,7 @@ struct vdpctx {
         } *targets;
         int targets_size;
         int render_count;
-        int bitmap_id;
-        int bitmap_pos_id;
+        int change_id;
     } osd_surfaces[MAX_OSD_PARTS];
 
     // Video equalizer
@@ -388,7 +387,7 @@ static void mark_vdpau_objects_uninitialized(struct vo *vo)
     for (int i = 0; i < MAX_OSD_PARTS; i++) {
         struct osd_bitmap_surface *sfc = &vc->osd_surfaces[i];
         talloc_free(sfc->packer);
-        sfc->bitmap_id = sfc->bitmap_pos_id = 0;
+        sfc->change_id = 0;
         *sfc = (struct osd_bitmap_surface){
             .surface = VDP_INVALID_HANDLE,
         };
@@ -512,7 +511,7 @@ static void generate_osd_part(struct vo *vo, struct sub_bitmaps *imgs)
     struct osd_bitmap_surface *sfc = &vc->osd_surfaces[imgs->render_index];
     bool need_upload = false;
 
-    if (imgs->bitmap_pos_id == sfc->bitmap_pos_id)
+    if (imgs->change_id == sfc->change_id)
         return; // Nothing changed and we still have the old data
 
     sfc->render_count = 0;
@@ -520,9 +519,6 @@ static void generate_osd_part(struct vo *vo, struct sub_bitmaps *imgs)
     if (imgs->format == SUBBITMAP_EMPTY || imgs->num_parts == 0)
         return;
 
-    if (imgs->bitmap_id == sfc->bitmap_id)
-        goto osd_skip_upload;
-
     need_upload = true;
     VdpRGBAFormat format;
     int format_size;
@@ -574,7 +570,6 @@ static void generate_osd_part(struct vo *vo, struct sub_bitmaps *imgs)
                                  sfc->packer->used_height});
     }
 
-osd_skip_upload:
     if (sfc->surface == VDP_INVALID_HANDLE)
         return;
     if (sfc->packer->count > sfc->targets_size) {
@@ -610,8 +605,7 @@ osd_skip_upload:
         sfc->render_count++;
     }
 
-    sfc->bitmap_id = imgs->bitmap_id;
-    sfc->bitmap_pos_id = imgs->bitmap_pos_id;
+    sfc->change_id = imgs->change_id;
 }
 
 static void draw_osd_cb(void *ctx, struct sub_bitmaps *imgs)
diff --git a/video/out/vo_wayland.c b/video/out/vo_wayland.c
index 9da24ddf3e..c179bbe179 100644
--- a/video/out/vo_wayland.c
+++ b/video/out/vo_wayland.c
@@ -134,7 +134,7 @@ struct priv {
     struct wl_subsurface *osd_subsurfaces[MAX_OSD_PARTS];
     shm_buffer_t *osd_buffers[MAX_OSD_PARTS];
     // this id tells us if the subtitle part has changed or not
-    int bitmap_pos_id[MAX_OSD_PARTS];
+    int change_id[MAX_OSD_PARTS];
 
     int64_t recent_flip_time; // last frame event
 
@@ -455,8 +455,8 @@ static void draw_osd_cb(void *ctx, struct sub_bitmaps *imgs)
 
     struct wl_surface *s = p->osd_surfaces[id];
 
-    if (imgs->bitmap_pos_id != p->bitmap_pos_id[id]) {
-        p->bitmap_pos_id[id] = imgs->bitmap_pos_id;
+    if (imgs->change_id != p->change_id[id]) {
+        p->change_id[id] = imgs->change_id;
 
         struct mp_rect bb;
         if (!mp_sub_bitmaps_bb(imgs, &bb))