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, errno, "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, errno, "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, errno, "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, errno, "failed to open `%s'", path);
 119
 120         nread = read(fd, res, st.st_size);
 121         if (nread - st.st_size)
 122                 err(1, errno, "read %llu failed, ret=%zd",
 123                     st.st_size+0llu, nread);
 124
 125         *len = (int) st.st_size;
 126         return res;
 127 }
 128
 129 static FT_Face load_font(const char *fontname)
 130 {
 131         FT_Face face;
 132         int code, len;
 133         void *base;
 134
 135         if (g_freetype_lib == NULL)
 136         {
 137                 init_font_cache();
 138                 clear_font_cache();
 139         }
 140
 141         base = filecontents(fontname, &len);
 142         code = FT_New_Memory_Face(g_freetype_lib, base, len, 0, &face);
 143         if (code)
 144         {
 145                 errx(1, "FT_New_Memory_Face for `%s' failed: %d",
 146                      fontname, code);
 147         }
 148
 149         FT_Select_Charmap(face, ft_encoding_unicode);
 150         return face;
 151 }
 152
 153 static FT_Face load_builtin_font(const void *base, int len)
 154 {
 155         FT_Face face;
 156         int code;
 157
 158         if (g_freetype_lib == NULL)
 159         {
 160                 init_font_cache();
 161                 clear_font_cache();
 162         }
 163
 164         code = FT_New_Memory_Face(g_freetype_lib, base, len, 0, &face);
 165         if (code)
 166         {
 167                 errx (1, "failed to load builtin font: %d\n", code);
 168                 return NULL;
 169         }
 170
 171         FT_Select_Charmap(face, ft_encoding_unicode);
 172         return face;
 173 }
 174
 175 static void UNUSED_ATTR free_font(FT_Face face)
 176 {
 177         clear_font_cache();
 178         FT_Done_Face(face);
 179 }
 180
 181 static unsigned int hashfunc(struct key *key)
 182 {
 183         unsigned char *buf = (unsigned char *)key;
 184         unsigned int len = sizeof(struct key);
 185         unsigned int h = 0;
 186         while (len--)
 187                 h = *buf++ + (h << 6) + (h << 16) - h;
 188         return h;
 189 }
 190
 191 static unsigned int lookup_table(struct key *key)
 192 {
 193         unsigned int pos = hashfunc(key) % MAXGLYPHS;
 194         while (1)
 195         {
 196                 if (!g_table[pos].key.face) /* empty slot */
 197                         return pos;
 198                 if (!memcmp(key, &g_table[pos].key, sizeof(struct key))) /* matching slot */
 199                         return pos;
 200                 pos = (pos + 1) % MAXGLYPHS;
 201         }
 202 }
 203
 204 static struct glyph * lookup_glyph(FT_Face face, int size, int gid, int subx, int suby)
 205 {
 206         FT_Vector subv;
 207         struct key key;
 208         unsigned int pos;
 209         int code;
 210         int w, h;
 211
 212         /*
 213          * Look it up in the table
 214          */
 215
 216         key.face = face;
 217         key.size = size;
 218         key.gid = gid;
 219         key.subx = subx;
 220         key.suby = suby;
 221
 222         pos = lookup_table(&key);
 223         if (g_table[pos].key.face)
 224                 return &g_table[pos].glyph;
 225
 226         /*
 227          * Render the bitmap
 228          */
 229         subv.x = subx;
 230         subv.y = suby;
 231
 232         FT_Set_Transform(face, NULL, &subv);
 233
 234         code = FT_Load_Glyph(face, gid, FT_LOAD_NO_BITMAP | FT_LOAD_NO_HINTING);
 235         if (code < 0)
 236                 return NULL;
 237
 238         code = FT_Render_Glyph(face->glyph, FT_RENDER_MODE_LIGHT);
 239         if (code < 0)
 240                 return NULL;
 241
 242         w = face->glyph->bitmap.width;
 243         h = face->glyph->bitmap.rows;
 244
 245         /*
 246          * Find an empty slot in the texture
 247          */
 248
 249         if (g_table_load == (MAXGLYPHS * 3) / 4)
 250         {
 251                 clear_font_cache();
 252                 pos = lookup_table(&key);
 253         }
 254
 255         if (h + PADDING > g_cache_h || w + PADDING > g_cache_w)
 256                 errx(1, "rendered glyph exceeds cache dimensions");
 257
 258         if (g_cache_row_x + w + PADDING > g_cache_w)
 259         {
 260                 g_cache_row_y += g_cache_row_h + PADDING;
 261                 g_cache_row_x = PADDING;
 262                 g_cache_row_h = 0;
 263         }
 264         if (g_cache_row_y + h + PADDING > g_cache_h)
 265         {
 266                 clear_font_cache();
 267                 pos = lookup_table(&key);
 268         }
 269
 270         /*
 271          * Copy bitmap into texture
 272          */
 273
 274         memcpy(&g_table[pos].key, &key, sizeof(struct key));
 275         g_table[pos].glyph.w = face->glyph->bitmap.width;
 276         g_table[pos].glyph.h = face->glyph->bitmap.rows;
 277         g_table[pos].glyph.lsb = face->glyph->bitmap_left;
 278         g_table[pos].glyph.top = face->glyph->bitmap_top;
 279         g_table[pos].glyph.s = g_cache_row_x;
 280         g_table[pos].glyph.t = g_cache_row_y;
 281         g_table[pos].glyph.advance = face->glyph->advance.x / 64.0;
 282         g_table_load ++;
 283
 284         glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
 285         glPixelStorei(GL_UNPACK_ROW_LENGTH, face->glyph->bitmap.pitch);
 286         glTexSubImage2D(GL_TEXTURE_2D, 0, g_cache_row_x, g_cache_row_y, w, h,
 287                         GL_ALPHA, GL_UNSIGNED_BYTE, face->glyph->bitmap.buffer);
 288         glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
 289
 290         g_cache_row_x += w + PADDING;
 291         if (g_cache_row_h < h + PADDING)
 292                 g_cache_row_h = h + PADDING;
 293
 294         return &g_table[pos].glyph;
 295 }
 296
 297 static float draw_glyph(FT_Face face, int size, int gid, float x, float y)
 298 {
 299         struct glyph *glyph;
 300         int subx = (x - floor(x)) * XPRECISION;
 301         int suby = (y - floor(y)) * YPRECISION;
 302         GLfloat *t = state.texcoords;
 303         GLfloat *v = state.vertices;
 304         float s0, t0, s1, t1, xc, yc;
 305
 306         subx = (subx * 64) / XPRECISION;
 307         suby = (suby * 64) / YPRECISION;
 308
 309         glyph = lookup_glyph(face, size, gid, subx, suby);
 310         if (!glyph)
 311                 return 0.0;
 312
 313         s0 = (float) glyph->s / g_cache_w;
 314         t0 = (float) glyph->t / g_cache_h;
 315         s1 = (float) (glyph->s + glyph->w) / g_cache_w;
 316         t1 = (float) (glyph->t + glyph->h) / g_cache_h;
 317         xc = floor(x) + glyph->lsb;
 318         yc = floor(y) - glyph->top + glyph->h;
 319
 320         t[0] = s0; t[1] = t0; v[0] = xc;            v[1] = yc - glyph->h;
 321         t[2] = s1; t[3] = t0; v[2] = xc + glyph->w; v[3] = yc - glyph->h;
 322         t[4] = s0; t[5] = t1; v[4] = xc;            v[5] = yc;
 323         t[6] = s1; t[7] = t1; v[6] = xc + glyph->w; v[7] = yc;
 324
 325         glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 326         return glyph->advance;
 327 }
 328
 329 static float measure_string(FT_Face face, float fsize, const char *str)
 330 {
 331         int size = fsize * 64;
 332         FT_Fixed advance;
 333         Rune ucs, gid;
 334         float w = 0.0;
 335         int left = 0;
 336
 337         FT_Set_Char_Size(face, size, size, 72, 72);
 338
 339         while (*str)
 340         {
 341                 str += fz_chartorune(&ucs, str);
 342                 gid = FT_Get_Char_Index(face, ucs);
 343                 FT_Get_Advance(face, gid, FT_LOAD_NO_BITMAP | FT_LOAD_NO_HINTING, &advance);
 344                 w += advance / 65536.0;
 345                 if (g_use_kern) {
 346                     FT_Vector kern;
 347
 348                     FT_Get_Kerning(face, left, gid, FT_KERNING_UNFITTED, &kern);
 349                     w += kern.x / 64.0;
 350                 }
 351                 left = gid;
 352         }
 353
 354         return w;
 355 }
 356
 357 static float draw_string(FT_Face face, float fsize, float x, float y,
 358                          const char *str)
 359 {
 360         int size = fsize * 64;
 361         Rune ucs, gid;
 362         int left = 0;
 363
 364         FT_Set_Char_Size(face, size, size, 72, 72);
 365
 366         glBindTexture(GL_TEXTURE_2D, g_cache_tex);
 367         glVertexPointer(2, GL_FLOAT, 0, state.vertices);
 368         glTexCoordPointer(2, GL_FLOAT, 0, state.texcoords);
 369
 370         while (*str)
 371         {
 372                 str += fz_chartorune(&ucs, str);
 373                 gid = FT_Get_Char_Index(face, ucs);
 374                 x += draw_glyph(face, size, gid, x, y);
 375                 if (g_use_kern) {
 376                     FT_Vector kern;
 377
 378                     FT_Get_Kerning(face, left, gid, FT_KERNING_UNFITTED, &kern);
 379                     x += kern.x / 64.0;
 380                 }
 381                 left = gid;
 382         }
 383
 384         return x;
 385 }
 386 /*
 387   Local Variables:
 388   c-file-style: "linux"
 389   End:
 390 */