Font Stash

Font stash is light-weight online font texture atlas builder written in C. It uses stb_truetype to render fonts on demand to a texture atlas.

The code is split in two parts, the font atlas and glyph quad generator fontstash.h, and an example OpenGL backend (glstash.h.

Screenshot

Example

// Create GL stash for 512x512 texture, our coordinate system has zero at top-left.
struct FONScontext* fs = glfonsCreate(512, 512, FONS_ZERO_TOPLEFT);

// Add font to stash.
int fontNormal = fonsAddFont(fs, "sans", "DroidSerif-Regular.ttf");

// Render some text
float dx = 10, dy = 10;
unsigned int white = glfonsRGBA(255,255,255,255);
unsigned int brown = glfonsRGBA(192,128,0,128);

fonsSetFont(fs, fontNormal);
fonsSetSize(fs, 124.0f);
fonsSetColor(fs, white);
fonsDrawText(fs, dx,dy,"The big ", NULL);

fonsSetSize(fs, 24.0f);
fonsSetColor(fs, brown);
fonsDrawText(fs, dx,dy,"brown fox", NULL);

Using Font Stash in your project

In order to use fontstash in your own project, just copy fontstash.h, stb_truetype.h, and potentially glstash.h to your project. In one C/C++ define FONTSTASH_IMPLEMENTATION before including the library to expand the font stash implementation in that file.

#include <stdio.h>					// malloc, free, fopen, fclose, ftell, fseek, fread
#include <string.h>					// memset
#define FONTSTASH_IMPLEMENTATION	// Expands implementation
#include "fontstash.h"

#include <GLFW/glfw3.h>				// Or any other GL header of your choice.
#define GLFONTSTASH_IMPLEMENTATION	// Expands implementation
#include "glfontstash.h"

Creating new rendering backend

The default rendering backend uses OpenGL to render the glyphs. If you want to render the text using some other API, or want tighter integration with your code base you can write your own rendering backend. Take a look at the glfontstash.h for reference implementation.

The rendering interface FontStash assumes access to is defined in the FONSparams structure. The renderer initialization function is assumed to fill in the FONSparams structure and call fonsCreateInternal to create the FontStash context.

struct FONSparams {
	...
	void* userPtr;
	int (*renderCreate)(void* uptr, int width, int height);
	int (*renderResize)(void* uptr, int width, int height);
	void (*renderUpdate)(void* uptr, int* rect, const unsigned char* data);
	void (*renderDraw)(void* uptr, const float* verts, const float* tcoords, const unsigned int* colors, int nverts);
	void (*renderDelete)(void* uptr);
};

• renderCreate is called to create renderer for specific API, this is where you should create a texture of given size.
  • return 1 of success, or 0 on failure.
• renderResize is called to resize the texture. Called when user explicitly expands or resets the atlas texture.
  • return 1 of success, or 0 on failure.
• renderUpdate is called to update texture data
  • rect describes the region of the texture that has changed
  • data pointer to full texture data
• renderDraw is called when the font triangles should be drawn
  • verts pointer to vertex position data, 2 floats per vertex
  • tcoords pointer to texture coordinate data, 2 floats per vertex
  • colors pointer to color data, 1 uint per vertex (or 4 bytes)
  • nverts is the number of vertices to draw
• renderDelete is called when the renderer should be deleted
• userPtr is passed to all calls as first parameter

FontStash uses this API as follows:

fonsDrawText() {
	foreach (glyph in input string) {
		if (internal buffer full) {
			updateTexture()
			render()
		}
		add glyph to interal draw buffer
	}
	updateTexture()
	render()
}

The size of the internal buffer is defined using FONS_VERTEX_COUNT define. The default value is 1024, you can override it when you include fontstash.h and specify the implementation:

#define FONS_VERTEX_COUNT 2048
#define FONTSTASH_IMPLEMENTATION	// Expands implementation
#include "fontstash.h"

OpenGL 3+ support

When using font stash with OpenGL 3 you run into problems due to OGLs switch to using vertex arrays, vertex buffers and removal of the fixed rendering pipeline. Simply include gl3fontstash.h instead of glfontstash.h to use the OpenGL 3 render additions.

Note that this requires an extension manager to be used such as GLEW and that a new function called gl3fonsProjection must be called before rendering text.

GLfloat mat[16];

memset(mat, 0, 16 * sizeof(GLfloat));
mat[0] = 2.0 / screenwidth;
mat[5] = -2.0 / screenheight;
mat[10] = 2.0;
mat[12] = -1.0;
mat[13] = 1.0;
mat[14] = -1.0;
mat[15] = 1.0;

gl3fonsProjection(mFS, mat);

License

The library is licensed under zlib license

Links

Uses stb_truetype for font rendering.