Support for underline and strikethrough

Add support for the underline (\u) and strikethrough/strikeout (\s)
properties.  This is a bit tricky, since FreeType doesn't offer
any method of adding the lines, so you have to draw them yourself.
libass uses various information from TrueType tables to get position
and size of the lines, does a few simple consistency checks (some fonts
might be broken) and if everything is alright, adds new contours for
the lines.

Sometimes, rendering errors can occur:
- Currently, kerning isn't taken into account, which means the lines
can overlap a little, leading to small optical glitches.
- Some (broken) fonts use the wrong winding direction.  In this case,
the FreeType stroker will only consider the added lines to be "outside"
and only stroke the line instead of the whole glyph.

1 files changed, 19 insertions, 1 deletions

diff --git a/libass/ass_render.c b/libass/ass_render.c
index c112399b..19870a55 100644
--- a/libass/ass_render.c
+++ b/libass/ass_render.c
@@ -144,6 +144,7 @@ typedef struct render_context_s {
     ass_font_t *font;
     char *font_path;
     double font_size;
+    int flags;                  // decoration flags (underline/strike-through)
 
     FT_Stroker stroker_x;
     FT_Stroker stroker_y;
@@ -1561,6 +1562,18 @@ static char *parse_tag(ass_renderer_t *render_priv, char *p, double pwr)
         } else
             val = 0.;
         render_priv->state.shadow_x = render_priv->state.shadow_y = val;
+    } else if (mystrcmp(&p, "s")) {
+        int val;
+        if (mystrtoi(&p, &val) && val)
+            render_priv->state.flags |= DECO_STRIKETHROUGH;
+        else
+            render_priv->state.flags &= ~DECO_STRIKETHROUGH;
+    } else if (mystrcmp(&p, "u")) {
+        int val;
+        if (mystrtoi(&p, &val) && val)
+            render_priv->state.flags |= DECO_UNDERLINE;
+        else
+            render_priv->state.flags &= ~DECO_UNDERLINE;
     } else if (mystrcmp(&p, "pbo")) {
         double val = 0;
         if (mystrtod(&p, &val))
@@ -1716,6 +1729,9 @@ static void reset_render_context(ass_renderer_t *render_priv)
     render_priv->state.c[1] = render_priv->state.style->SecondaryColour;
     render_priv->state.c[2] = render_priv->state.style->OutlineColour;
     render_priv->state.c[3] = render_priv->state.style->BackColour;
+    render_priv->state.flags =
+        (render_priv->state.style->Underline ? DECO_UNDERLINE : 0) |
+        (render_priv->state.style->StrikeOut ? DECO_STRIKETHROUGH : 0);
     render_priv->state.font_size = render_priv->state.style->FontSize;
 
     if (render_priv->state.family)
@@ -1904,6 +1920,7 @@ get_outline_glyph(ass_renderer_t *render_priv, int symbol,
         key.advance = *advance;
         key.outline.x = render_priv->state.border_x * 0xFFFF;
         key.outline.y = render_priv->state.border_y * 0xFFFF;
+        key.flags = render_priv->state.flags;
     }
     memset(info, 0, sizeof(glyph_info_t));
 
@@ -1928,7 +1945,8 @@ get_outline_glyph(ass_renderer_t *render_priv, int symbol,
             info->glyph =
                 ass_font_get_glyph(render_priv->fontconfig_priv,
                                    render_priv->state.font, symbol,
-                                   render_priv->settings.hinting);
+                                   render_priv->settings.hinting,
+                                   render_priv->state.flags);
         }
         if (!info->glyph)
             return;