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 = malloc(g_cache_w * g_cache_h);
  86         memset(zero, 0, g_cache_w * g_cache_h);
  87         glBindTexture(GL_TEXTURE_2D, g_cache_tex);
  88         glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, g_cache_w, g_cache_h, GL_ALPHA, GL_UNSIGNED_BYTE, zero);
  89         free(zero);
  90 #endif
  91
  92         memset(g_table, 0, sizeof(g_table));
  93         g_table_load = 0;
  94
  95         g_cache_row_y = PADDING;
  96         g_cache_row_x = PADDING;
  97         g_cache_row_h = 0;
  98 }
  99
 100 static FT_Face load_font(char *fontname)
 101 {
 102         FT_Face face;
 103         int code;
 104
 105         if (g_freetype_lib == NULL)
 106         {
 107                 init_font_cache();
 108                 clear_font_cache();
 109         }
 110
 111         code = FT_New_Face (g_freetype_lib, fontname, 0, &face);
 112         if (code) {
 113             fprintf (stderr, "failed to load font `%s'\n", fontname);
 114             return NULL;
 115         }
 116
 117         FT_Select_Charmap(face, ft_encoding_unicode);
 118         return face;
 119 }
 120
 121 static FT_Face load_builtin_font(void *base, int len)
 122 {
 123         FT_Face face;
 124         int code;
 125
 126         if (g_freetype_lib == NULL)
 127         {
 128                 init_font_cache();
 129                 clear_font_cache();
 130         }
 131
 132         code = FT_New_Memory_Face(g_freetype_lib, base, len, 0, &face);
 133         if (code) {
 134             fprintf (stderr, "failed to load builtin font\n");
 135             return NULL;
 136         }
 137
 138         FT_Select_Charmap(face, ft_encoding_unicode);
 139         return face;
 140 }
 141
 142 static void UNUSED free_font(FT_Face face)
 143 {
 144         clear_font_cache();
 145         FT_Done_Face(face);
 146 }
 147
 148 static unsigned int hashfunc(struct key *key)
 149 {
 150         unsigned char *buf = (unsigned char *)key;
 151         unsigned int len = sizeof(struct key);
 152         unsigned int h = 0;
 153         while (len--)
 154                 h = *buf++ + (h << 6) + (h << 16) - h;
 155         return h;
 156 }
 157
 158 static unsigned int lookup_table(struct key *key)
 159 {
 160         unsigned int pos = hashfunc(key) % MAXGLYPHS;
 161         while (1)
 162         {
 163                 if (!g_table[pos].key.face) /* empty slot */
 164                         return pos;
 165                 if (!memcmp(key, &g_table[pos].key, sizeof(struct key))) /* matching slot */
 166                         return pos;
 167                 pos = (pos + 1) % MAXGLYPHS;
 168         }
 169 }
 170
 171 static struct glyph * lookup_glyph(FT_Face face, int size, int gid, int subx, int suby)
 172 {
 173         FT_Vector subv;
 174         struct key key;
 175         unsigned int pos;
 176         int code;
 177         int w, h;
 178
 179         /*
 180          * Look it up in the table
 181          */
 182
 183         key.face = face;
 184         key.size = size;
 185         key.gid = gid;
 186         key.subx = subx;
 187         key.suby = suby;
 188
 189         pos = lookup_table(&key);
 190         if (g_table[pos].key.face)
 191                 return &g_table[pos].glyph;
 192
 193         /*
 194          * Render the bitmap
 195          */
 196
 197         glEnd();
 198
 199         subv.x = subx;
 200         subv.y = suby;
 201
 202         FT_Set_Transform(face, NULL, &subv);
 203
 204         code = FT_Load_Glyph(face, gid, FT_LOAD_NO_BITMAP | FT_LOAD_NO_HINTING);
 205         if (code < 0)
 206                 return NULL;
 207
 208         code = FT_Render_Glyph(face->glyph, FT_RENDER_MODE_LIGHT);
 209         if (code < 0)
 210                 return NULL;
 211
 212         w = face->glyph->bitmap.width;
 213         h = face->glyph->bitmap.rows;
 214
 215         /*
 216          * Find an empty slot in the texture
 217          */
 218
 219         if (g_table_load == (MAXGLYPHS * 3) / 4)
 220         {
 221                 lprintf("font cache table full, clearing cache");
 222                 clear_font_cache();
 223                 pos = lookup_table(&key);
 224         }
 225
 226         if (h + PADDING > g_cache_h || w + PADDING > g_cache_w)
 227                 errx(1, "rendered glyph exceeds cache dimensions");
 228
 229         if (g_cache_row_x + w + PADDING > g_cache_w)
 230         {
 231                 g_cache_row_y += g_cache_row_h + PADDING;
 232                 g_cache_row_x = PADDING;
 233         }
 234         if (g_cache_row_y + h + PADDING > g_cache_h)
 235         {
 236                 lprintf("font cache texture full, clearing cache");
 237                 clear_font_cache();
 238                 pos = lookup_table(&key);
 239         }
 240
 241         /*
 242          * Copy bitmap into texture
 243          */
 244
 245         memcpy(&g_table[pos].key, &key, sizeof(struct key));
 246         g_table[pos].glyph.w = face->glyph->bitmap.width;
 247         g_table[pos].glyph.h = face->glyph->bitmap.rows;
 248         g_table[pos].glyph.lsb = face->glyph->bitmap_left;
 249         g_table[pos].glyph.top = face->glyph->bitmap_top;
 250         g_table[pos].glyph.s = g_cache_row_x;
 251         g_table[pos].glyph.t = g_cache_row_y;
 252         g_table[pos].glyph.advance = face->glyph->advance.x / 64.0;
 253         g_table_load ++;
 254
 255         glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
 256         glPixelStorei(GL_UNPACK_ROW_LENGTH, face->glyph->bitmap.pitch);
 257         glTexSubImage2D(GL_TEXTURE_2D, 0, g_cache_row_x, g_cache_row_y, w, h,
 258                         GL_ALPHA, GL_UNSIGNED_BYTE, face->glyph->bitmap.buffer);
 259         glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
 260
 261         glBegin(GL_QUADS);
 262
 263         g_cache_row_x += w + PADDING;
 264         if (g_cache_row_h < h + PADDING)
 265                 g_cache_row_h = h + PADDING;
 266
 267         return &g_table[pos].glyph;
 268 }
 269
 270 static float draw_glyph(FT_Face face, int size, int gid, float x, float y)
 271 {
 272         struct glyph *glyph;
 273         int subx = (x - floor(x)) * XPRECISION;
 274         int suby = (y - floor(y)) * YPRECISION;
 275         subx = (subx * 64) / XPRECISION;
 276         suby = (suby * 64) / YPRECISION;
 277
 278         glyph = lookup_glyph(face, size, gid, subx, suby);
 279         if (!glyph)
 280                 return 0.0;
 281
 282         float s0 = (float) glyph->s / g_cache_w;
 283         float t0 = (float) glyph->t / g_cache_h;
 284         float s1 = (float) (glyph->s + glyph->w) / g_cache_w;
 285         float t1 = (float) (glyph->t + glyph->h) / g_cache_h;
 286         float xc = floor(x) + glyph->lsb;
 287         float yc = floor(y) - glyph->top + glyph->h;
 288
 289         glTexCoord2f(s0, t0); glVertex2f(xc, yc - glyph->h);
 290         glTexCoord2f(s1, t0); glVertex2f(xc + glyph->w, yc - glyph->h);
 291         glTexCoord2f(s1, t1); glVertex2f(xc + glyph->w, yc);
 292         glTexCoord2f(s0, t1); glVertex2f(xc, yc);
 293
 294         return glyph->advance;
 295 }
 296
 297 static float measure_string(FT_Face face, float fsize, char *str)
 298 {
 299         int size = fsize * 64;
 300         FT_Fixed advance;
 301         FT_Vector kern;
 302         Rune ucs, gid;
 303         float w = 0.0;
 304         int left = 0;
 305
 306         FT_Set_Char_Size(face, size, size, 72, 72);
 307
 308         while (*str)
 309         {
 310                 str += chartorune(&ucs, str);
 311                 gid = FT_Get_Char_Index(face, ucs);
 312                 FT_Get_Advance(face, gid, FT_LOAD_NO_BITMAP | FT_LOAD_NO_HINTING, &advance);
 313                 w += advance / 65536.0;
 314                 FT_Get_Kerning(face, left, gid, FT_KERNING_UNFITTED, &kern);
 315                 w += kern.x / 64.0;
 316                 left = gid;
 317         }
 318
 319         return w;
 320 }
 321
 322 static float draw_string(FT_Face face, float fsize, float x, float y, char *str)
 323 {
 324         int size = fsize * 64;
 325         FT_Vector kern;
 326         Rune ucs, gid;
 327         int left = 0;
 328
 329         FT_Set_Char_Size(face, size, size, 72, 72);
 330
 331         glBindTexture(GL_TEXTURE_2D, g_cache_tex);
 332         glBegin(GL_QUADS);
 333
 334         while (*str)
 335         {
 336                 str += chartorune(&ucs, str);
 337                 gid = FT_Get_Char_Index(face, ucs);
 338                 x += draw_glyph(face, size, gid, x, y);
 339                 FT_Get_Kerning(face, left, gid, FT_KERNING_UNFITTED, &kern);
 340                 x += kern.x / 64.0;
 341                 left = gid;
 342         }
 343
 344         glEnd();
 345
 346         return x;
 347 }