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 FT_Face load_font(char *fontname)
 103 {
 104         FT_Face face;
 105         int code;
 106
 107         if (g_freetype_lib == NULL)
 108         {
 109                 init_font_cache();
 110                 clear_font_cache();
 111         }
 112
 113         code = FT_New_Face (g_freetype_lib, fontname, 0, &face);
 114         if (code) {
 115                 fprintf (stderr, "failed to load font `%s'\n", fontname);
 116                 return NULL;
 117         }
 118
 119         FT_Select_Charmap(face, ft_encoding_unicode);
 120         return face;
 121 }
 122
 123 static FT_Face UNUSED_ATTR load_builtin_font(void *base, int len)
 124 {
 125         FT_Face face;
 126         int code;
 127
 128         if (g_freetype_lib == NULL)
 129         {
 130                 init_font_cache();
 131                 clear_font_cache();
 132         }
 133
 134         code = FT_New_Memory_Face(g_freetype_lib, base, len, 0, &face);
 135         if (code) {
 136                 fprintf (stderr, "failed to load builtin font\n");
 137                 return NULL;
 138         }
 139
 140         FT_Select_Charmap(face, ft_encoding_unicode);
 141         return face;
 142 }
 143
 144 static void UNUSED_ATTR free_font(FT_Face face)
 145 {
 146         clear_font_cache();
 147         FT_Done_Face(face);
 148 }
 149
 150 static unsigned int hashfunc(struct key *key)
 151 {
 152         unsigned char *buf = (unsigned char *)key;
 153         unsigned int len = sizeof(struct key);
 154         unsigned int h = 0;
 155         while (len--)
 156                 h = *buf++ + (h << 6) + (h << 16) - h;
 157         return h;
 158 }
 159
 160 static unsigned int lookup_table(struct key *key)
 161 {
 162         unsigned int pos = hashfunc(key) % MAXGLYPHS;
 163         while (1)
 164         {
 165                 if (!g_table[pos].key.face) /* empty slot */
 166                         return pos;
 167                 if (!memcmp(key, &g_table[pos].key, sizeof(struct key))) /* matching slot */
 168                         return pos;
 169                 pos = (pos + 1) % MAXGLYPHS;
 170         }
 171 }
 172
 173 static struct glyph * lookup_glyph(FT_Face face, int size, int gid, int subx, int suby)
 174 {
 175         FT_Vector subv;
 176         struct key key;
 177         unsigned int pos;
 178         int code;
 179         int w, h;
 180
 181         /*
 182          * Look it up in the table
 183          */
 184
 185         key.face = face;
 186         key.size = size;
 187         key.gid = gid;
 188         key.subx = subx;
 189         key.suby = suby;
 190
 191         pos = lookup_table(&key);
 192         if (g_table[pos].key.face)
 193                 return &g_table[pos].glyph;
 194
 195         /*
 196          * Render the bitmap
 197          */
 198
 199         glEnd();
 200
 201         subv.x = subx;
 202         subv.y = suby;
 203
 204         FT_Set_Transform(face, NULL, &subv);
 205
 206         code = FT_Load_Glyph(face, gid, FT_LOAD_NO_BITMAP | FT_LOAD_NO_HINTING);
 207         if (code < 0)
 208                 return NULL;
 209
 210         code = FT_Render_Glyph(face->glyph, FT_RENDER_MODE_LIGHT);
 211         if (code < 0)
 212                 return NULL;
 213
 214         w = face->glyph->bitmap.width;
 215         h = face->glyph->bitmap.rows;
 216
 217         /*
 218          * Find an empty slot in the texture
 219          */
 220
 221         if (g_table_load == (MAXGLYPHS * 3) / 4)
 222         {
 223                 lprintf("font cache table full, clearing cache");
 224                 clear_font_cache();
 225                 pos = lookup_table(&key);
 226         }
 227
 228         if (h + PADDING > g_cache_h || w + PADDING > g_cache_w)
 229                 errx(1, "rendered glyph exceeds cache dimensions");
 230
 231         if (g_cache_row_x + w + PADDING > g_cache_w)
 232         {
 233                 g_cache_row_y += g_cache_row_h + PADDING;
 234                 g_cache_row_x = PADDING;
 235         }
 236         if (g_cache_row_y + h + PADDING > g_cache_h)
 237         {
 238                 lprintf("font cache texture full, clearing cache");
 239                 clear_font_cache();
 240                 pos = lookup_table(&key);
 241         }
 242
 243         /*
 244          * Copy bitmap into texture
 245          */
 246
 247         memcpy(&g_table[pos].key, &key, sizeof(struct key));
 248         g_table[pos].glyph.w = face->glyph->bitmap.width;
 249         g_table[pos].glyph.h = face->glyph->bitmap.rows;
 250         g_table[pos].glyph.lsb = face->glyph->bitmap_left;
 251         g_table[pos].glyph.top = face->glyph->bitmap_top;
 252         g_table[pos].glyph.s = g_cache_row_x;
 253         g_table[pos].glyph.t = g_cache_row_y;
 254         g_table[pos].glyph.advance = face->glyph->advance.x / 64.0;
 255         g_table_load ++;
 256
 257         glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
 258         glPixelStorei(GL_UNPACK_ROW_LENGTH, face->glyph->bitmap.pitch);
 259         glTexSubImage2D(GL_TEXTURE_2D, 0, g_cache_row_x, g_cache_row_y, w, h,
 260                         GL_ALPHA, GL_UNSIGNED_BYTE, face->glyph->bitmap.buffer);
 261         glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
 262
 263         glBegin(GL_QUADS);
 264
 265         g_cache_row_x += w + PADDING;
 266         if (g_cache_row_h < h + PADDING)
 267                 g_cache_row_h = h + PADDING;
 268
 269         return &g_table[pos].glyph;
 270 }
 271
 272 static float draw_glyph(FT_Face face, int size, int gid, float x, float y)
 273 {
 274         struct glyph *glyph;
 275         int subx = (x - floor(x)) * XPRECISION;
 276         int suby = (y - floor(y)) * YPRECISION;
 277         subx = (subx * 64) / XPRECISION;
 278         suby = (suby * 64) / YPRECISION;
 279
 280         glyph = lookup_glyph(face, size, gid, subx, suby);
 281         if (!glyph)
 282                 return 0.0;
 283
 284         float s0 = (float) glyph->s / g_cache_w;
 285         float t0 = (float) glyph->t / g_cache_h;
 286         float s1 = (float) (glyph->s + glyph->w) / g_cache_w;
 287         float t1 = (float) (glyph->t + glyph->h) / g_cache_h;
 288         float xc = floor(x) + glyph->lsb;
 289         float yc = floor(y) - glyph->top + glyph->h;
 290
 291         glTexCoord2f(s0, t0); glVertex2f(xc, yc - glyph->h);
 292         glTexCoord2f(s1, t0); glVertex2f(xc + glyph->w, yc - glyph->h);
 293         glTexCoord2f(s1, t1); glVertex2f(xc + glyph->w, yc);
 294         glTexCoord2f(s0, t1); glVertex2f(xc, yc);
 295
 296         return glyph->advance;
 297 }
 298
 299 static float measure_string(FT_Face face, float fsize, char *str)
 300 {
 301         int size = fsize * 64;
 302         FT_Fixed advance;
 303         Rune ucs, gid;
 304         float w = 0.0;
 305         int left = 0;
 306
 307         FT_Set_Char_Size(face, size, size, 72, 72);
 308
 309         while (*str)
 310         {
 311                 str += fz_chartorune(&ucs, str);
 312                 gid = FT_Get_Char_Index(face, ucs);
 313                 FT_Get_Advance(face, gid, FT_LOAD_NO_BITMAP | FT_LOAD_NO_HINTING, &advance);
 314                 w += advance / 65536.0;
 315                 if (g_use_kern) {
 316                     FT_Vector kern;
 317
 318                     FT_Get_Kerning(face, left, gid, FT_KERNING_UNFITTED, &kern);
 319                     w += kern.x / 64.0;
 320                 }
 321                 left = gid;
 322         }
 323
 324         return w;
 325 }
 326
 327 static float draw_string(FT_Face face, float fsize, float x, float y, char *str)
 328 {
 329         int size = fsize * 64;
 330         Rune ucs, gid;
 331         int left = 0;
 332
 333         FT_Set_Char_Size(face, size, size, 72, 72);
 334
 335         glBindTexture(GL_TEXTURE_2D, g_cache_tex);
 336         glBegin(GL_QUADS);
 337
 338         while (*str)
 339         {
 340                 str += fz_chartorune(&ucs, str);
 341                 gid = FT_Get_Char_Index(face, ucs);
 342                 x += draw_glyph(face, size, gid, x, y);
 343                 if (g_use_kern) {
 344                     FT_Vector kern;
 345
 346                     FT_Get_Kerning(face, left, gid, FT_KERNING_UNFITTED, &kern);
 347                     x += kern.x / 64.0;
 348                 }
 349                 left = gid;
 350         }
 351
 352         glEnd();
 353
 354         return x;
 355 }