fontselect: overhaul font scoring and faux-ing; fixes libass#437

This emulates GDI's behavior, both around scoring and faux decisions.

The fontconfig provider doesn't provide the full information we'd need to handle this 100% accurately, so it's best-guessed.

libass/ass_font.c

@@ -548,6 +548,29 @@ int ass_face_get_weight(FT_Face face)
     }
 }
 
+static FT_Long fsSelection_to_style_flags(uint16_t fsSelection)
+{
+    FT_Long ret = 0;
+
+    if (fsSelection & 1)
+        ret |= FT_STYLE_FLAG_ITALIC;
+    if (fsSelection & (1 << 5))
+        ret |= FT_STYLE_FLAG_BOLD;
+
+    return ret;
+}
+
+FT_Long ass_face_get_style_flags(FT_Face face)
+{
+    // If we have an OS/2 table, compute this ourselves, since FreeType
+    // will mix in some flags that GDI ignores.
+    TT_OS2 *os2 = FT_Get_Sfnt_Table(face, FT_SFNT_OS2);
+    if (os2)
+        return fsSelection_to_style_flags(os2->fsSelection);
+
+    return face->style_flags;
+}
+
 /**
  * \brief Get maximal font ascender and descender.
  **/
@@ -693,9 +716,12 @@ bool ass_font_get_glyph(ASS_Font *font, int face_index, int index,
                 index);
         return false;
     }
-    if (!(face->style_flags & FT_STYLE_FLAG_ITALIC) && (font->desc.italic > 55))
+
+    FT_Long style_flags = ass_face_get_style_flags(face);
+    if (!(style_flags & FT_STYLE_FLAG_ITALIC) && (font->desc.italic > 55))
         ass_glyph_italicize(face->glyph);
-    if (font->desc.bold > ass_face_get_weight(face) + 150)
+    if (!(style_flags & FT_STYLE_FLAG_BOLD) &&
+        font->desc.bold > ass_face_get_weight(face) + 150)
         ass_glyph_embolden(face->glyph);
     return true;
 }

libass/ass_font.h

@@ -52,6 +52,7 @@ void ass_charmap_magic(ASS_Library *library, FT_Face face);
 ASS_Font *ass_font_new(ASS_Renderer *render_priv, ASS_FontDesc *desc);
 void ass_face_set_size(FT_Face face, double size);
 int ass_face_get_weight(FT_Face face);
+FT_Long ass_face_get_style_flags(FT_Face face);
 void ass_font_get_asc_desc(ASS_Font *font, int face_index,
                            int *asc, int *desc);
 int ass_font_get_index(ASS_FontSelector *fontsel, ASS_Font *font,

libass/ass_fontconfig.c

@@ -98,6 +98,7 @@ static void scan_fonts(FcConfig *config, ASS_FontProvider *provider)
         FcBool outline;
         int index;
         double weight;
+        int slant;
         char *path;
         char *fullnames[MAX_NAME];
         char *families[MAX_NAME];
@@ -108,7 +109,7 @@ static void scan_fonts(FcConfig *config, ASS_FontProvider *provider)
             continue;
 
         // simple types
-        result  = FcPatternGetInteger(pat, FC_SLANT, 0, &meta.slant);
+        result  = FcPatternGetInteger(pat, FC_SLANT, 0, &slant);
         result |= FcPatternGetDouble(pat, FC_WEIGHT, 0, &weight);
         result |= FcPatternGetInteger(pat, FC_INDEX, 0, &index);
         if (result != FcResultMatch)
@@ -158,6 +159,9 @@ static void scan_fonts(FcConfig *config, ASS_FontProvider *provider)
             meta.weight = 1000;
 #endif
 
+        // Take a guess at the italic flag
+        meta.style_flags = (slant >= FC_SLANT_ITALIC) ? FT_STYLE_FLAG_ITALIC : 0;
+
         // path
         result = FcPatternGetString(pat, FC_FILE, 0, (FcChar8 **)&path);
         if (result != FcResultMatch)

libass/ass_fontselect.c

@@ -34,6 +34,7 @@
 #include FT_FREETYPE_H
 #include FT_SFNT_NAMES_H
 #include FT_TRUETYPE_IDS_H
+#include FT_TRUETYPE_TABLES_H
 #include FT_TYPE1_TABLES_H
 
 #include "ass_utils.h"
@@ -60,8 +61,8 @@ struct font_info {
     int n_family;
     int n_fullname;
 
-    int slant;
-    int weight;         // TrueType scale, 100-900
+    FT_Long style_flags;
+    int weight;           // TrueType scale, 100-900
 
     // how to access this face
     char *path;            // absolute path
@@ -256,7 +257,6 @@ get_font_info(FT_Library lib, FT_Face face, const char *fallback_family_name,
     int num_fullname = 0;
     int num_family   = 0;
     int num_names = FT_Get_Sfnt_Name_Count(face);
-    int slant, weight;
     char *fullnames[MAX_FULLNAME];
     char *families[MAX_FULLNAME];
     PS_FontInfoRec postscript_info;
@@ -309,13 +309,9 @@ get_font_info(FT_Library lib, FT_Face face, const char *fallback_family_name,
     if (num_family == 0)
         goto error;
 
-    // calculate sensible slant and weight from style attributes
-    slant  = 110 * !!(face->style_flags & FT_STYLE_FLAG_ITALIC);
-    weight = ass_face_get_weight(face);
-
-    // fill our struct
-    info->slant  = slant;
-    info->weight = weight;
+    // calculate sensible weight
+    info->weight = ass_face_get_weight(face);
+    info->style_flags = ass_face_get_style_flags(face);
 
     info->postscript_name = (char *)FT_Get_Postscript_Name(face);
     info->is_postscript = !FT_Get_PS_Font_Info(face, &postscript_info);
@@ -389,7 +385,6 @@ ass_font_provider_add_font(ASS_FontProvider *provider,
                            int index, void *data)
 {
     int i;
-    int weight, slant;
     ASS_FontSelector *selector = provider->parent;
     ASS_FontInfo *info = NULL;
     ASS_FontProviderMetaData implicit_meta = {0};
@@ -445,21 +440,12 @@ ass_font_provider_add_font(ASS_FontProvider *provider,
     for (j = 0; j < meta->n_fullname; j++)
         printf("'%s' ", meta->fullnames[j]);
     printf("\n");
-    printf("  slant: %d\n", meta->slant);
+    printf("  style_flags: %lx\n", meta->style_flags);
     printf("  weight: %d\n", meta->weight);
     printf("  path: %s\n", path);
     printf("  index: %d\n", index);
 #endif
 
-    weight = meta->weight;
-    slant  = meta->slant;
-
-    // check slant/weight for validity, use defaults if they're invalid
-    if (weight < 100 || weight > 900)
-        weight = 400;
-    if (slant < 0 || slant > 110)
-        slant = 0;
-
     // check size
     if (selector->n_font >= selector->alloc_font) {
         selector->alloc_font = FFMAX(1, 2 * selector->alloc_font);
@@ -474,8 +460,8 @@ ass_font_provider_add_font(ASS_FontProvider *provider,
     // set uid
     info->uid = selector->uid++;
 
-    info->slant         = slant;
-    info->weight        = weight;
+    info->style_flags   = meta->style_flags;
+    info->weight        = meta->weight;
     info->n_fullname    = meta->n_fullname;
     info->n_family      = meta->n_family;
     info->is_postscript = meta->is_postscript;
@@ -668,11 +654,26 @@ static bool matches_full_or_postscript_name(ASS_FontInfo *f,
  */
 static unsigned font_attributes_similarity(ASS_FontInfo *a, ASS_FontInfo *req)
 {
-    unsigned similarity = 0;
-    similarity += ABS(a->weight - req->weight);
-    similarity += ABS(a->slant - req->slant);
+    unsigned score = 0;
+
+    // Assign score for italics mismatch
+    if ((req->style_flags & FT_STYLE_FLAG_ITALIC) &&
+        !(a->style_flags & FT_STYLE_FLAG_ITALIC))
+        score += 1;
+    else if (!(req->style_flags & FT_STYLE_FLAG_ITALIC) &&
+             (a->style_flags & FT_STYLE_FLAG_ITALIC))
+        score += 4;
+
+    int a_weight = a->weight;
+
+    // Offset effective weight for faux-bold (only if font isn't flagged as bold)
+    if ((req->weight > a->weight + 150) && !(a->style_flags & FT_STYLE_FLAG_BOLD))
+        a_weight += 120;
+
+    // Assign score for weight mismatch
+    score += (73 * ABS(a_weight - req->weight)) / 256;
 
-    return similarity;
+    return score;
 }
 
 #if 0
@@ -724,8 +725,8 @@ find_font(ASS_FontSelector *priv,
         return NULL;
 
     // fill font request
-    req.slant   = italic;
-    req.weight  = bold;
+    req.style_flags = (italic ? FT_STYLE_FLAG_ITALIC : 0);
+    req.weight      = bold;
 
     // Match font family name against font list
     unsigned score_min = UINT_MAX;

libass/ass_fontselect.h

@@ -205,7 +205,7 @@ struct ass_font_provider_meta_data {
     int n_family;       // Number of localized family names
     int n_fullname;     // Number of localized full names
 
-    int slant;          // Font slant value from FONT_SLANT_*
+    FT_Long style_flags; // Computed from OS/2 table, or equivalent
     int weight;         // Font weight in TrueType scale, 100-900
                         // See FONT_WEIGHT_*