glfont.c

   1 /* This is a slightly modified
   2    https://github.com/ccxvii/snippets/blob/master/glfont.c by Tor Andersson
   3 */
   4 /*
   5  * A very simple font cache and rasterizer that uses freetype
   6  * to draw fonts from a single OpenGL texture. The code uses
   7  * a linear-probe hashtable, and writes new glyphs into
   8  * the texture using glTexSubImage2D. When the texture fills
   9  * up, or the hash table gets too crowded, everything is wiped.
  10  *
  11  * This is designed to be used for horizontal text only,
  12  * and draws unhinted text with subpixel accurate metrics
  13  * and kerning. As such, you should always call the drawing
  14  * function with an identity transform that maps units
  15  * to pixels accurately.
  16  *
  17  * If you wish to use it to draw arbitrarily transformed
  18  * text, change the min and mag filters to GL_LINEAR and
  19  * add a pixel of padding between glyphs and rows, and
  20  * make sure to clear the texture when wiping the cache.
  21  */
  22
  23 #include FT_ADVANCES_H
  24 typedef int Rune;               /* 32 bits */
  25
  26 #define PADDING 1               /* set to 0 to save some space but disallow arbitrary transforms */
  27
  28 #define MAXGLYPHS 4093  /* prime number for hash table goodness */
  29 #define CACHESIZE 256
  30 #define XPRECISION 4
  31 #define YPRECISION 1
  32
  33 struct key
  34 {
  35         FT_Face face;
  36         short size;
  37         short gid;
  38         short subx;
  39         short suby;
  40 };
  41
  42 struct glyph
  43 {
  44         signed char lsb, top, w, h;
  45         short s, t;
  46         float advance;
  47 };
  48
  49 struct table
  50 {
  51         struct key key;
  52         struct glyph glyph;
  53 };
  54
  55 static FT_Library g_freetype_lib = NULL;
  56 static struct table g_table[MAXGLYPHS];
  57 static int g_table_load = 0;
  58 static unsigned int g_cache_tex = 0;
  59 static int g_cache_w = CACHESIZE;
  60 static int g_cache_h = CACHESIZE;
  61 static int g_cache_row_y = 0;
  62 static int g_cache_row_x = 0;
  63 static int g_cache_row_h = 0;
  64 static int g_use_kern = 0;
  65
  66 static void init_font_cache(void)
  67 {
  68         int code;
  69
  70         code = FT_Init_FreeType(&g_freetype_lib);
  71         if (code)
  72                 errx(1, "cannot initialize freetype");
  73
  74         glGenTextures(1, &g_cache_tex);
  75         glBindTexture(GL_TEXTURE_2D, g_cache_tex);
  76         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
  77         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
  78         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
  79         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
  80         glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, g_cache_w, g_cache_h, 0, GL_ALPHA, GL_UNSIGNED_BYTE, NULL);
  81 }
  82
  83 static void clear_font_cache(void)
  84 {
  85 #if PADDING > 0
  86         unsigned char *zero = calloc(g_cache_w, g_cache_h);
  87         if (!zero)
  88                 err(1, "malloc zero (%u bytes failed)", g_cache_w * g_cache_h);
  89         glBindTexture(GL_TEXTURE_2D, g_cache_tex);
  90         glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, g_cache_w, g_cache_h, GL_ALPHA, GL_UNSIGNED_BYTE, zero);
  91         free(zero);
  92 #endif
  93
  94         memset(g_table, 0, sizeof(g_table));
  95         g_table_load = 0;
  96
  97         g_cache_row_y = PADDING;
  98         g_cache_row_x = PADDING;
  99         g_cache_row_h = 0;
 100 }
 101
 102 static void *filecontents (const char *path, int *len)
 103 {
 104         int ret, fd;
 105         void *res;
 106         struct stat st;
 107         ssize_t nread;
 108
 109         ret = stat(path, &st);
 110         if (ret) err(1, "failed to stat `%s'", path);
 111         if (st.st_size > INT_MAX) errx(1, "font `%s' is too big", path);
 112         res = malloc(st.st_size);
 113         if (!res)
 114                 err(1, "failed to allocate %llu bytes for `%s'",
 115                     st.st_size+0ull, path);
 116
 117         fd = open(path, O_RDONLY);
 118         if (fd < 0) err(1, "failed to open `%s'", path);
 119
 120         nread = read(fd, res, st.st_size);
 121         if (nread - st.st_size)
 122                 err(1, "read %llu failed, ret=%zd", st.st_size+0llu, nread);
 123
 124         *len = (int) st.st_size;
 125         return res;
 126 }
 127
 128 static FT_Face load_font(const char *fontname)
 129 {
 130         FT_Face face;
 131         int code, len;
 132         void *base;
 133
 134         if (g_freetype_lib == NULL)
 135         {
 136                 init_font_cache();
 137                 clear_font_cache();
 138         }
 139
 140         base = filecontents(fontname, &len);
 141         code = FT_New_Memory_Face(g_freetype_lib, base, len, 0, &face);
 142         if (code)
 143         {
 144                 errx(1, "FT_New_Memory_Face for `%s' failed: %d",
 145                      fontname, code);
 146         }
 147
 148         FT_Select_Charmap(face, ft_encoding_unicode);
 149         return face;
 150 }
 151
 152 static FT_Face load_builtin_font(const void *base, int len)
 153 {
 154         FT_Face face;
 155         int code;
 156
 157         if (g_freetype_lib == NULL)
 158         {
 159                 init_font_cache();
 160                 clear_font_cache();
 161         }
 162
 163         code = FT_New_Memory_Face(g_freetype_lib, base, len, 0, &face);
 164         if (code)
 165         {
 166                 errx (1, "failed to load builtin font: %d\n", code);
 167                 return NULL;
 168         }
 169
 170         FT_Select_Charmap(face, ft_encoding_unicode);
 171         return face;
 172 }
 173
 174 static void UNUSED_ATTR free_font(FT_Face face)
 175 {
 176         clear_font_cache();
 177         FT_Done_Face(face);
 178 }
 179
 180 static unsigned int hashfunc(struct key *key)
 181 {
 182         unsigned char *buf = (unsigned char *)key;
 183         unsigned int len = sizeof(struct key);
 184         unsigned int h = 0;
 185         while (len--)
 186                 h = *buf++ + (h << 6) + (h << 16) - h;
 187         return h;
 188 }
 189
 190 static unsigned int lookup_table(struct key *key)
 191 {
 192         unsigned int pos = hashfunc(key) % MAXGLYPHS;
 193         while (1)
 194         {
 195                 if (!g_table[pos].key.face) /* empty slot */
 196                         return pos;
 197                 if (!memcmp(key, &g_table[pos].key, sizeof(struct key))) /* matching slot */
 198                         return pos;
 199                 pos = (pos + 1) % MAXGLYPHS;
 200         }
 201 }
 202
 203 static struct glyph * lookup_glyph(FT_Face face, int size, int gid, int subx, int suby)
 204 {
 205         FT_Vector subv;
 206         struct key key;
 207         unsigned int pos;
 208         int code;
 209         int w, h;
 210
 211         /*
 212          * Look it up in the table
 213          */
 214
 215         key.face = face;
 216         key.size = size;
 217         key.gid = gid;
 218         key.subx = subx;
 219         key.suby = suby;
 220
 221         pos = lookup_table(&key);
 222         if (g_table[pos].key.face)
 223                 return &g_table[pos].glyph;
 224
 225         /*
 226          * Render the bitmap
 227          */
 228 #ifdef FFP
 229         glEnd();
 230 #endif
 231
 232         subv.x = subx;
 233         subv.y = suby;
 234
 235         FT_Set_Transform(face, NULL, &subv);
 236
 237         code = FT_Load_Glyph(face, gid, FT_LOAD_NO_BITMAP | FT_LOAD_NO_HINTING);
 238         if (code < 0)
 239                 return NULL;
 240
 241         code = FT_Render_Glyph(face->glyph, FT_RENDER_MODE_LIGHT);
 242         if (code < 0)
 243                 return NULL;
 244
 245         w = face->glyph->bitmap.width;
 246         h = face->glyph->bitmap.rows;
 247
 248         /*
 249          * Find an empty slot in the texture
 250          */
 251
 252         if (g_table_load == (MAXGLYPHS * 3) / 4)
 253         {
 254                 lprintf("font cache table full, clearing cache");
 255                 clear_font_cache();
 256                 pos = lookup_table(&key);
 257         }
 258
 259         if (h + PADDING > g_cache_h || w + PADDING > g_cache_w)
 260                 errx(1, "rendered glyph exceeds cache dimensions");
 261
 262         if (g_cache_row_x + w + PADDING > g_cache_w)
 263         {
 264                 g_cache_row_y += g_cache_row_h + PADDING;
 265                 g_cache_row_x = PADDING;
 266                 g_cache_row_h = 0;
 267         }
 268         if (g_cache_row_y + h + PADDING > g_cache_h)
 269         {
 270                 lprintf("font cache texture full, clearing cache");
 271                 clear_font_cache();
 272                 pos = lookup_table(&key);
 273         }
 274
 275         /*
 276          * Copy bitmap into texture
 277          */
 278
 279         memcpy(&g_table[pos].key, &key, sizeof(struct key));
 280         g_table[pos].glyph.w = face->glyph->bitmap.width;
 281         g_table[pos].glyph.h = face->glyph->bitmap.rows;
 282         g_table[pos].glyph.lsb = face->glyph->bitmap_left;
 283         g_table[pos].glyph.top = face->glyph->bitmap_top;
 284         g_table[pos].glyph.s = g_cache_row_x;
 285         g_table[pos].glyph.t = g_cache_row_y;
 286         g_table[pos].glyph.advance = face->glyph->advance.x / 64.0;
 287         g_table_load ++;
 288
 289         glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
 290         glPixelStorei(GL_UNPACK_ROW_LENGTH, face->glyph->bitmap.pitch);
 291         glTexSubImage2D(GL_TEXTURE_2D, 0, g_cache_row_x, g_cache_row_y, w, h,
 292                         GL_ALPHA, GL_UNSIGNED_BYTE, face->glyph->bitmap.buffer);
 293         glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
 294
 295 #ifdef FFP
 296         glBegin(GL_QUADS);
 297 #endif
 298         g_cache_row_x += w + PADDING;
 299         if (g_cache_row_h < h + PADDING)
 300                 g_cache_row_h = h + PADDING;
 301
 302         return &g_table[pos].glyph;
 303 }
 304
 305 static float draw_glyph(FT_Face face, int size, int gid, float x, float y)
 306 {
 307         struct glyph *glyph;
 308         int subx = (x - floor(x)) * XPRECISION;
 309         int suby = (y - floor(y)) * YPRECISION;
 310 #ifndef FFP
 311         GLfloat *t = state.texcoords;
 312         GLfloat *v = state.vertices;
 313 #endif
 314         float s0, t0, s1, t1, xc, yc;
 315
 316         subx = (subx * 64) / XPRECISION;
 317         suby = (suby * 64) / YPRECISION;
 318
 319         glyph = lookup_glyph(face, size, gid, subx, suby);
 320         if (!glyph)
 321                 return 0.0;
 322
 323         s0 = (float) glyph->s / g_cache_w;
 324         t0 = (float) glyph->t / g_cache_h;
 325         s1 = (float) (glyph->s + glyph->w) / g_cache_w;
 326         t1 = (float) (glyph->t + glyph->h) / g_cache_h;
 327         xc = floor(x) + glyph->lsb;
 328         yc = floor(y) - glyph->top + glyph->h;
 329
 330 #ifndef FFP
 331         t[0] = s0; t[1] = t0; v[0] = xc;            v[1] = yc - glyph->h;
 332         t[2] = s1; t[3] = t0; v[2] = xc + glyph->w; v[3] = yc - glyph->h;
 333         t[4] = s0; t[5] = t1; v[4] = xc;            v[5] = yc;
 334         t[6] = s1; t[7] = t1; v[6] = xc + glyph->w; v[7] = yc;
 335
 336         glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 337 #else
 338         glTexCoord2f(s0, t0); glVertex2f(xc, yc - glyph->h);
 339         glTexCoord2f(s1, t0); glVertex2f(xc + glyph->w, yc - glyph->h);
 340         glTexCoord2f(s1, t1); glVertex2f(xc + glyph->w, yc);
 341         glTexCoord2f(s0, t1); glVertex2f(xc, yc);
 342 #endif
 343
 344         return glyph->advance;
 345 }
 346
 347 static float measure_string(FT_Face face, float fsize, const char *str)
 348 {
 349         int size = fsize * 64;
 350         FT_Fixed advance;
 351         Rune ucs, gid;
 352         float w = 0.0;
 353         int left = 0;
 354
 355         FT_Set_Char_Size(face, size, size, 72, 72);
 356
 357         while (*str)
 358         {
 359                 str += fz_chartorune(&ucs, str);
 360                 gid = FT_Get_Char_Index(face, ucs);
 361                 FT_Get_Advance(face, gid, FT_LOAD_NO_BITMAP | FT_LOAD_NO_HINTING, &advance);
 362                 w += advance / 65536.0;
 363                 if (g_use_kern) {
 364                     FT_Vector kern;
 365
 366                     FT_Get_Kerning(face, left, gid, FT_KERNING_UNFITTED, &kern);
 367                     w += kern.x / 64.0;
 368                 }
 369                 left = gid;
 370         }
 371
 372         return w;
 373 }
 374
 375 static float draw_string(FT_Face face, float fsize, float x, float y,
 376                          const char *str)
 377 {
 378         int size = fsize * 64;
 379         Rune ucs, gid;
 380         int left = 0;
 381
 382         FT_Set_Char_Size(face, size, size, 72, 72);
 383
 384         glBindTexture(GL_TEXTURE_2D, g_cache_tex);
 385 #ifdef FFP
 386         glBegin(GL_QUADS);
 387 #else
 388         glVertexPointer(2, GL_FLOAT, 0, state.vertices);
 389         glTexCoordPointer(2, GL_FLOAT, 0, state.texcoords);
 390 #endif
 391         while (*str)
 392         {
 393                 str += fz_chartorune(&ucs, str);
 394                 gid = FT_Get_Char_Index(face, ucs);
 395                 x += draw_glyph(face, size, gid, x, y);
 396                 if (g_use_kern) {
 397                     FT_Vector kern;
 398
 399                     FT_Get_Kerning(face, left, gid, FT_KERNING_UNFITTED, &kern);
 400                     x += kern.x / 64.0;
 401                 }
 402                 left = gid;
 403         }
 404
 405 #ifdef FFP
 406         glEnd();
 407 #endif
 408
 409         return x;
 410 }
 411 /*
 412   Local Variables:
 413   c-file-style: "linux"
 414   End:
 415 */