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
  65 static void init_font_cache(void)
  66 {
  67         int code;
  68
  69         code = FT_Init_FreeType(&g_freetype_lib);
  70         if (code)
  71                 errx(1, "cannot initialize freetype");
  72
  73         glGenTextures(1, &g_cache_tex);
  74         glBindTexture(GL_TEXTURE_2D, g_cache_tex);
  75         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
  76         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
  77         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
  78         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
  79         glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, g_cache_w, g_cache_h, 0, GL_ALPHA, GL_UNSIGNED_BYTE, NULL);
  80 }
  81
  82 static void clear_font_cache(void)
  83 {
  84 #if PADDING > 0
  85         unsigned char *zero = calloc(g_cache_w, g_cache_h);
  86         if (!zero)
  87                 err(1, "malloc zero (%u bytes failed)", g_cache_w * g_cache_h);
  88         glBindTexture(GL_TEXTURE_2D, g_cache_tex);
  89         glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, g_cache_w, g_cache_h, GL_ALPHA, GL_UNSIGNED_BYTE, zero);
  90         free(zero);
  91 #endif
  92
  93         memset(g_table, 0, sizeof(g_table));
  94         g_table_load = 0;
  95
  96         g_cache_row_y = PADDING;
  97         g_cache_row_x = PADDING;
  98         g_cache_row_h = 0;
  99 }
 100
 101 static FT_Face load_font(char *fontname)
 102 {
 103         FT_Face face;
 104         int code;
 105
 106         if (g_freetype_lib == NULL)
 107         {
 108                 init_font_cache();
 109                 clear_font_cache();
 110         }
 111
 112         code = FT_New_Face (g_freetype_lib, fontname, 0, &face);
 113         if (code) {
 114                 fprintf (stderr, "failed to load font `%s'\n", fontname);
 115                 return NULL;
 116         }
 117
 118         FT_Select_Charmap(face, ft_encoding_unicode);
 119         return face;
 120 }
 121
 122 static FT_Face load_builtin_font(void *base, int len)
 123 {
 124         FT_Face face;
 125         int code;
 126
 127         if (g_freetype_lib == NULL)
 128         {
 129                 init_font_cache();
 130                 clear_font_cache();
 131         }
 132
 133         code = FT_New_Memory_Face(g_freetype_lib, base, len, 0, &face);
 134         if (code) {
 135                 fprintf (stderr, "failed to load builtin font\n");
 136                 return NULL;
 137         }
 138
 139         FT_Select_Charmap(face, ft_encoding_unicode);
 140         return face;
 141 }
 142
 143 static void UNUSED free_font(FT_Face face)
 144 {
 145         clear_font_cache();
 146         FT_Done_Face(face);
 147 }
 148
 149 static unsigned int hashfunc(struct key *key)
 150 {
 151         unsigned char *buf = (unsigned char *)key;
 152         unsigned int len = sizeof(struct key);
 153         unsigned int h = 0;
 154         while (len--)
 155                 h = *buf++ + (h << 6) + (h << 16) - h;
 156         return h;
 157 }
 158
 159 static unsigned int lookup_table(struct key *key)
 160 {
 161         unsigned int pos = hashfunc(key) % MAXGLYPHS;
 162         while (1)
 163         {
 164                 if (!g_table[pos].key.face) /* empty slot */
 165                         return pos;
 166                 if (!memcmp(key, &g_table[pos].key, sizeof(struct key))) /* matching slot */
 167                         return pos;
 168                 pos = (pos + 1) % MAXGLYPHS;
 169         }
 170 }
 171
 172 static struct glyph * lookup_glyph(FT_Face face, int size, int gid, int subx, int suby)
 173 {
 174         FT_Vector subv;
 175         struct key key;
 176         unsigned int pos;
 177         int code;
 178         int w, h;
 179
 180         /*
 181          * Look it up in the table
 182          */
 183
 184         key.face = face;
 185         key.size = size;
 186         key.gid = gid;
 187         key.subx = subx;
 188         key.suby = suby;
 189
 190         pos = lookup_table(&key);
 191         if (g_table[pos].key.face)
 192                 return &g_table[pos].glyph;
 193
 194         /*
 195          * Render the bitmap
 196          */
 197
 198         glEnd();
 199
 200         subv.x = subx;
 201         subv.y = suby;
 202
 203         FT_Set_Transform(face, NULL, &subv);
 204
 205         code = FT_Load_Glyph(face, gid, FT_LOAD_NO_BITMAP | FT_LOAD_NO_HINTING);
 206         if (code < 0)
 207                 return NULL;
 208
 209         code = FT_Render_Glyph(face->glyph, FT_RENDER_MODE_LIGHT);
 210         if (code < 0)
 211                 return NULL;
 212
 213         w = face->glyph->bitmap.width;
 214         h = face->glyph->bitmap.rows;
 215
 216         /*
 217          * Find an empty slot in the texture
 218          */
 219
 220         if (g_table_load == (MAXGLYPHS * 3) / 4)
 221         {
 222                 lprintf("font cache table full, clearing cache");
 223                 clear_font_cache();
 224                 pos = lookup_table(&key);
 225         }
 226
 227         if (h + PADDING > g_cache_h || w + PADDING > g_cache_w)
 228                 errx(1, "rendered glyph exceeds cache dimensions");
 229
 230         if (g_cache_row_x + w + PADDING > g_cache_w)
 231         {
 232                 g_cache_row_y += g_cache_row_h + PADDING;
 233                 g_cache_row_x = PADDING;
 234         }
 235         if (g_cache_row_y + h + PADDING > g_cache_h)
 236         {
 237                 lprintf("font cache texture full, clearing cache");
 238                 clear_font_cache();
 239                 pos = lookup_table(&key);
 240         }
 241
 242         /*
 243          * Copy bitmap into texture
 244          */
 245
 246         memcpy(&g_table[pos].key, &key, sizeof(struct key));
 247         g_table[pos].glyph.w = face->glyph->bitmap.width;
 248         g_table[pos].glyph.h = face->glyph->bitmap.rows;
 249         g_table[pos].glyph.lsb = face->glyph->bitmap_left;
 250         g_table[pos].glyph.top = face->glyph->bitmap_top;
 251         g_table[pos].glyph.s = g_cache_row_x;
 252         g_table[pos].glyph.t = g_cache_row_y;
 253         g_table[pos].glyph.advance = face->glyph->advance.x / 64.0;
 254         g_table_load ++;
 255
 256         glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
 257         glPixelStorei(GL_UNPACK_ROW_LENGTH, face->glyph->bitmap.pitch);
 258         glTexSubImage2D(GL_TEXTURE_2D, 0, g_cache_row_x, g_cache_row_y, w, h,
 259                         GL_ALPHA, GL_UNSIGNED_BYTE, face->glyph->bitmap.buffer);
 260         glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
 261
 262         glBegin(GL_QUADS);
 263
 264         g_cache_row_x += w + PADDING;
 265         if (g_cache_row_h < h + PADDING)
 266                 g_cache_row_h = h + PADDING;
 267
 268         return &g_table[pos].glyph;
 269 }
 270
 271 static float draw_glyph(FT_Face face, int size, int gid, float x, float y)
 272 {
 273         struct glyph *glyph;
 274         int subx = (x - floor(x)) * XPRECISION;
 275         int suby = (y - floor(y)) * YPRECISION;
 276         subx = (subx * 64) / XPRECISION;
 277         suby = (suby * 64) / YPRECISION;
 278
 279         glyph = lookup_glyph(face, size, gid, subx, suby);
 280         if (!glyph)
 281                 return 0.0;
 282
 283         float s0 = (float) glyph->s / g_cache_w;
 284         float t0 = (float) glyph->t / g_cache_h;
 285         float s1 = (float) (glyph->s + glyph->w) / g_cache_w;
 286         float t1 = (float) (glyph->t + glyph->h) / g_cache_h;
 287         float xc = floor(x) + glyph->lsb;
 288         float yc = floor(y) - glyph->top + glyph->h;
 289
 290         glTexCoord2f(s0, t0); glVertex2f(xc, yc - glyph->h);
 291         glTexCoord2f(s1, t0); glVertex2f(xc + glyph->w, yc - glyph->h);
 292         glTexCoord2f(s1, t1); glVertex2f(xc + glyph->w, yc);
 293         glTexCoord2f(s0, t1); glVertex2f(xc, yc);
 294
 295         return glyph->advance;
 296 }
 297
 298 static float measure_string(FT_Face face, float fsize, char *str)
 299 {
 300         int size = fsize * 64;
 301         FT_Fixed advance;
 302         FT_Vector kern;
 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 += 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                 FT_Get_Kerning(face, left, gid, FT_KERNING_UNFITTED, &kern);
 316                 w += kern.x / 64.0;
 317                 left = gid;
 318         }
 319
 320         return w;
 321 }
 322
 323 static float draw_string(FT_Face face, float fsize, float x, float y, char *str)
 324 {
 325         int size = fsize * 64;
 326         FT_Vector kern;
 327         Rune ucs, gid;
 328         int left = 0;
 329
 330         FT_Set_Char_Size(face, size, size, 72, 72);
 331
 332         glBindTexture(GL_TEXTURE_2D, g_cache_tex);
 333         glBegin(GL_QUADS);
 334
 335         while (*str)
 336         {
 337                 str += chartorune(&ucs, str);
 338                 gid = FT_Get_Char_Index(face, ucs);
 339                 x += draw_glyph(face, size, gid, x, y);
 340                 FT_Get_Kerning(face, left, gid, FT_KERNING_UNFITTED, &kern);
 341                 x += kern.x / 64.0;
 342                 left = gid;
 343         }
 344
 345         glEnd();
 346
 347         return x;
 348 }