ugui/text_rendering/font.c

#define _POSIX_C_SOURCE 200809l
#define STB_TRUETYPE_IMPLEMENTATION
#define STBTT_STATIC
#define MSDF_IMPLEMENTATION
#define STB_IMAGE_WRITE_IMPLEMENTATION

#include <grapheme.h>
#include <assert.h>

#include "font.h"
#include "msdf_c/stb_truetype.h"
#include "msdf_c/msdf.h"
#include "stb_image_write.h"
#include "util.h"
#include "cache.h"


#define UTF8(c) (c&0x80)
#define BDEPTH 3
#define BORDER 4

// Generates a cached atlas of font glyphs encoded usign a signed distance field
// https://www.youtube.com/watch?v=1b5hIMqz_wM
// https://github.com/pjako/msdf_c
// this way the texture atlas for the font will be bigger but we save up the space
// needed for rendering the font in multiple sizes

// as of now only monospaced fonts work correctly since no kerning information is stored 


const unsigned int glyph_w = 32;
const unsigned int glyph_h = 32;


struct priv {
	stbtt_fontinfo stb;
	msdf_AllocCtx ctx;
	msdf_Result msdf;
	float scale;
};
#define PRIV(x) ((struct priv *)x->priv)


// only useful for msdf_c
static inline void * _emalloc(size_t x, void *_) { (void)_; return emalloc(x); }
static inline void _efree(void *x, void *_) { (void)_; efree(x); }


struct font_atlas * font_init(void)
{
	struct font_atlas *p = emalloc(sizeof(struct font_atlas));
	memset(p, 0, sizeof(struct font_atlas));
	p->priv = emalloc(sizeof(struct priv));
	memset(p->priv, 0, sizeof(struct priv));
	return p;
}


// loads a font into memory, storing all the ASCII characters in the atlas
int font_load(struct font_atlas *atlas, const char *path)
{
	if (!atlas || !path)
		return -1;

	int err;

	dump_file(path, &(atlas->file), &(atlas->file_size));

	err = stbtt_InitFont(&(PRIV(atlas)->stb), (unsigned char *)atlas->file, 0);
	ERROR(err == 0, -1);

	PRIV(atlas)->scale = stbtt_ScaleForPixelHeight(&(PRIV(atlas)->stb), glyph_h);
	//int ascent, descent, linegap, baseline;
	//int x0,y0,x1,y1;
	//stbtt_GetFontVMetrics(&(PRIV(atlas)->stb), &ascent, &descent, &linegap);
	//stbtt_GetFontBoundingBox(&(PRIV(atlas)->stb), &x0, &y0, &x1, &y1);
	//baseline = PRIV(atlas)->scale * -y0;
	//atlas->glyph_max_w = (PRIV(atlas)->scale*x1) - (PRIV(atlas)->scale*x0);
	//atlas->glyph_max_h = (baseline+PRIV(atlas)->scale*y1) - (baseline+PRIV(atlas)->scale*y0);
	//atlas->atlas = emalloc(atlas->glyph_max_w*atlas->glyph_max_h*CACHE_SIZE);

	atlas->atlas  = emalloc(CACHE_SIZE*BDEPTH*glyph_h*glyph_w);
	memset(atlas->atlas, 0, CACHE_SIZE*BDEPTH*glyph_h*glyph_w);
	// FIXME: make this a square atlas
	atlas->width  = glyph_w*CACHE_SIZE/4;
	atlas->height = glyph_h*4;

	PRIV(atlas)->ctx = (msdf_AllocCtx){_emalloc, _efree, NULL};

	cache_init();

	// preallocate all ascii characters
	for (char c = ' '; c <= '~'; c++) {
		if (!font_get_glyph_texture(atlas, c, NULL))
			return -1;
	}

	return 0;
}


int font_free(struct font_atlas *atlas)
{
	efree(atlas->atlas);
	efree(atlas->file);
	efree(atlas->priv);
	efree(atlas);
	cache_destroy();
	return 0;
}


// FIXME: when generating the sdf I only use the height, so to not encounter memory
//        errors height and width must be equal
const struct font_glyph * font_get_glyph_texture(struct font_atlas *atlas, unsigned int code, int *updated)
{
	int u = 0;
	if (!updated) updated = &u;

	const struct font_glyph *r;
	if ((r = cache_search(code)) != NULL) {
		*updated = 0;
		return r;
	}

	*updated = 1;
	// generate the sdf and put it into the cache
	// TODO: generate the whole block at once
	int idx = stbtt_FindGlyphIndex(&PRIV(atlas)->stb, code);
	// FIXME: what happens if I change the range?
	int err;
	err = msdf_genGlyph(&PRIV(atlas)->msdf,
		&PRIV(atlas)->stb,
		idx,
		BORDER,
		PRIV(atlas)->scale,
		2.0f/glyph_h,
		&PRIV(atlas)->ctx);
	// msdf_genGlyph returns 0 only when there are no contours, so only for
	// whitespace and such, for those insert a zero uv map into the cache
	// FIXME: this is a waste of space
	if (!err) {
		PRIV(atlas)->msdf.width = 0;
		PRIV(atlas)->msdf.height = 0;
	}

	unsigned int spot = cache_get();
	unsigned int oy   = (glyph_h * spot) / atlas->width;
	unsigned int ox   = (glyph_h * spot) % atlas->height;
	unsigned int w    = atlas->width;

	// sum magic shit
	struct {unsigned char r,g,b;} *a = (void *)atlas->atlas;
	msdf_Result  *res = &PRIV(atlas)->msdf;
	float s  = glyph_h;
	float tw = ((s * 0.7f) + s) / (s * 2.0f);
	float ta = tw - 0.5f;
	float ts = 0.5 - ta / 2;
	float te = ts + ta;

	#define NORMALIZE(x) x = x > ts ? (x > te ? 1.0f : (x-ts)/ta+0.0f) : (0.0f)

	for (int y = 0; y < res->height; y++) {
	        int yPos = res->width * 3 * y;
		for (int x = 0; x < res->width; x++) {

			int i = yPos + (x * 3);
			float r = res->rgb[i+0];
			float g = res->rgb[i+1];
			float b = res->rgb[i+2];

			r = (r + s) / (s * 2.0f);
			g = (g + s) / (s * 2.0f);
			b = (b + s) / (s * 2.0f);

			NORMALIZE(r);
			NORMALIZE(g);
			NORMALIZE(b);

			a[(oy+y)*w + (ox+x)].r = r * 255.0f; // (r > 0.5f) ? 255.0f : r * 255.0f;
			a[(oy+y)*w + (ox+x)].g = g * 255.0f; // (g > 0.5f) ? 255.0f : g * 255.0f;
			a[(oy+y)*w + (ox+x)].b = b * 255.0f; // (b > 0.5f) ? 255.0f : b * 255.0f;
		}
	}

	struct font_glyph g = {
		.codepoint = code,
		.u = ox,
		.v = oy,
		.w = res->width,
		.h = res->height,
	};
	const struct font_glyph *ret = cache_insert(&g, spot);

	efree(PRIV(atlas)->msdf.rgb);

	return ret;
}


void font_dump(const struct font_atlas *atlas, const char *path)
{
	stbi_write_png(
		path,
		atlas->width,
		atlas->height,
		BDEPTH,
		atlas->atlas,
		BDEPTH*atlas->width);
}