Split glyph runs early

The "bitmap runs" that are currently used only when combining bitmaps
are also relevant at other stages, mainly for VSFilter compatibility.
They are not currently used because this information is not available
until bitmap combining (except during shaping, which has its own "shape
runs" that duplicate a good chunk of the "bitmap run" logic).

Move some code around to compute run boundaries as early as possible.
This lays the foundation for future commits that will make use this
information in more places where it can simplify code or improve
VSFilter compatibility.

For VSFilter compatibility, rather than break runs immediately upon line
breaks, break runs after line-leading whitespace, even in the first line.

These runs correspond to VSFilter's CWord instances.

3 files changed, 47 insertions, 42 deletions

diff --git a/libass/ass_parse.c b/libass/ass_parse.c
index 4134987..bb6fcff 100644
--- a/libass/ass_parse.c
+++ b/libass/ass_parse.c
@@ -1016,7 +1016,6 @@ void process_karaoke_effects(ASS_Renderer *render_priv)
                     cur2->effect_type = s1->effect_type;
                     cur2->effect_timing = x - d6_to_int(cur2->pos.x);
                 }
-                s1->effect = 1;
             }
         }
     }
diff --git a/libass/ass_render.c b/libass/ass_render.c
index ce9503a..df4b5de 100644
--- a/libass/ass_render.c
+++ b/libass/ass_render.c
@@ -1582,6 +1582,8 @@ static void trim_whitespace(ASS_Renderer *render_priv)
         cur->is_trimmed_whitespace = true;
         cur = ti->glyphs + ++i;
     }
+    if (i < ti->length)
+        cur->starts_new_run = true;
 
     // Mark all extraneous whitespace inbetween
     for (i = 0; i < ti->length; ++i) {
@@ -1610,6 +1612,8 @@ static void trim_whitespace(ASS_Renderer *render_priv)
                 }
                 i = j - 1;
             }
+            if (cur < ti->glyphs + ti->length)
+                cur->starts_new_run = true;
         }
     }
 }
@@ -1850,40 +1854,43 @@ fix_glyph_scaling(ASS_Renderer *priv, GlyphInfo *glyph)
     glyph->font_size = ft_size;
 }
 
- /**
-  * \brief Checks whether a glyph should start a new bitmap run
-  * \param info Pointer to new GlyphInfo to check
-  * \param current_info Pointer to CombinedBitmapInfo for current run (may be NULL)
-  * \return true if a new run should be started
-  */
-static bool is_new_bm_run(GlyphInfo *info, GlyphInfo *last)
+// Initial run splitting based purely on the characters' styles
+static void split_style_runs(ASS_Renderer *render_priv)
 {
-    return !last || info->effect || info->drawing_text || last->drawing_text ||
-        strcmp(last->font->desc.family, info->font->desc.family) ||
-        last->font->desc.vertical != info->font->desc.vertical ||
-        last->font_size != info->font_size ||
-        last->c[0] != info->c[0] ||
-        last->c[1] != info->c[1] ||
-        last->c[2] != info->c[2] ||
-        last->c[3] != info->c[3] ||
-        last->be != info->be ||
-        last->blur != info->blur ||
-        last->shadow_x != info->shadow_x ||
-        last->shadow_y != info->shadow_y ||
-        last->frx != info->frx ||
-        last->fry != info->fry ||
-        last->frz != info->frz ||
-        last->fax != info->fax ||
-        last->fay != info->fay ||
-        last->scale_x != info->scale_x ||
-        last->scale_y != info->scale_y ||
-        last->border_style != info->border_style ||
-        last->border_x != info->border_x ||
-        last->border_y != info->border_y ||
-        last->hspacing != info->hspacing ||
-        last->italic != info->italic ||
-        last->bold != info->bold ||
-        ((last->flags ^ info->flags) & ~DECO_ROTATE);
+    render_priv->text_info.glyphs[0].starts_new_run = true;
+    for (int i = 1; i < render_priv->text_info.length; i++) {
+        GlyphInfo *info = render_priv->text_info.glyphs + i;
+        GlyphInfo *last = render_priv->text_info.glyphs + (i - 1);
+        info->starts_new_run =
+            info->effect_type != EF_NONE ||
+            info->drawing_text ||
+            last->drawing_text ||
+            strcmp(last->font->desc.family, info->font->desc.family) ||
+            last->font->desc.vertical != info->font->desc.vertical ||
+            last->font_size != info->font_size ||
+            last->c[0] != info->c[0] ||
+            last->c[1] != info->c[1] ||
+            last->c[2] != info->c[2] ||
+            last->c[3] != info->c[3] ||
+            last->be != info->be ||
+            last->blur != info->blur ||
+            last->shadow_x != info->shadow_x ||
+            last->shadow_y != info->shadow_y ||
+            last->frx != info->frx ||
+            last->fry != info->fry ||
+            last->frz != info->frz ||
+            last->fax != info->fax ||
+            last->fay != info->fay ||
+            last->scale_x != info->scale_x ||
+            last->scale_y != info->scale_y ||
+            last->border_style != info->border_style ||
+            last->border_x != info->border_x ||
+            last->border_y != info->border_y ||
+            last->hspacing != info->hspacing ||
+            last->italic != info->italic ||
+            last->bold != info->bold ||
+            ((last->flags ^ info->flags) & ~DECO_ROTATE);
+    }
 }
 
 // Parse event text.
@@ -2273,14 +2280,13 @@ static void render_and_combine_glyphs(ASS_Renderer *render_priv,
     int left = render_priv->settings.left_margin;
     device_x = (device_x - left) * render_priv->font_scale_x + left;
     unsigned nb_bitmaps = 0;
-    char linebreak = 0;
+    bool new_run = true;
     CombinedBitmapInfo *combined_info = text_info->combined_bitmaps;
     CombinedBitmapInfo *current_info = NULL;
-    GlyphInfo *last_info = NULL;
     ASS_DVector offset;
     for (int i = 0; i < text_info->length; i++) {
         GlyphInfo *info = text_info->glyphs + i;
-        if (info->linebreak) linebreak = 1;
+        if (info->starts_new_run) new_run = true;
         if (info->skip) {
             for (; info; info = info->next)
                 ass_cache_dec_ref(info->outline);
@@ -2310,9 +2316,7 @@ static void render_and_combine_glyphs(ASS_Renderer *render_priv,
                 info->border_style == 3)
                 flags |= FILTER_FILL_IN_BORDER;
 
-            if (linebreak || is_new_bm_run(info, last_info)) {
-                linebreak = 0;
-                last_info = NULL;
+            if (new_run) {
                 if (nb_bitmaps >= text_info->max_bitmaps) {
                     size_t new_size = 2 * text_info->max_bitmaps;
                     if (!ASS_REALLOC_ARRAY(text_info->combined_bitmaps, new_size)) {
@@ -2357,8 +2361,8 @@ static void render_and_combine_glyphs(ASS_Renderer *render_priv,
                 current_info->max_bitmap_count = MAX_SUB_BITMAPS_INITIAL;
 
                 nb_bitmaps++;
+                new_run = false;
             }
-            last_info = info;
             assert(current_info);
 
             ASS_Vector pos, pos_o;
@@ -2606,6 +2610,8 @@ ass_render_event(ASS_Renderer *render_priv, ASS_Event *event,
         return false;
     }
 
+    split_style_runs(render_priv);
+
     // Find shape runs and shape text
     ass_shaper_set_base_direction(render_priv->shaper,
             resolve_base_direction(render_priv->state.font_encoding));
diff --git a/libass/ass_render.h b/libass/ass_render.h
index 4714dfa..2207850 100644
--- a/libass/ass_render.h
+++ b/libass/ass_render.h
@@ -143,11 +143,11 @@ typedef struct glyph_info {
     ASS_Vector pos;
     ASS_Vector offset;
     char linebreak;             // the first (leading) glyph of some line ?
+    bool starts_new_run;
     uint32_t c[4];              // colors
     uint8_t a_pre_fade[4];      // alpha values before applying fades
     ASS_Vector advance;         // 26.6
     ASS_Vector cluster_advance;
-    char effect;                // the first (leading) glyph of some effect ?
     Effect effect_type;
     int effect_timing;          // time duration of current karaoke word
     // after process_karaoke_effects: distance in pixels from the glyph origin.