sondro / vefontcache

Single-header minimalistic pragmatic GPU font rendering library.

VE Font Cache is a single header-only GPU font rendering library designed for game engines.

It aims to:

• Be fast and simple to integrate.
• Take advantage of modern GPU power.
• Be backend agnostic and easy to port to any API such as Vulkan, DirectX, OpenGL.
• Load TTF & OTF file formats directly.
• Use only runtime cache with no offline calculation.
• Render glyphs at reasonable quality at a wide range of font sizes.
• Support a good amount of internationalisation. そうですね!
• Support cached text shaping with HarfBuzz with simple Latin-style fallback.
• Load and unload fonts at any time.

How it works

Glyphs are GPU rasterised with 16x supersampling. This method is a simplification of "Easy Scalable Text Rendering on the GPU", by Evan Wallace, making use of XOR blending. Bézier curves are handled via brute force triangle tessellation; even 6 triangles per curve only generates < 300 triangles, which is nothing for modern GPUs! This avoids complex frag shader for reasonable quality.

Texture atlas caching uses naïve grid placement; this wastes a lot of space but ensures interchangeable cache slots allowing for straight up LRU ( Least Recently Used ) caching scheme to be employed.

The font atlas is a single 4k x 2k R8 texture divided into 4 regions:

     2k
     --------------------
     |         |        |
     |    A    |        |
     |         |        | 2
     |---------|    C   | k  
     |         |        |
  1k |    B    |        |
     |         |        |
     --------------------
     |                  |
     |                  |
     |                  | 2
     |        D         | k  
     |                  |
     |                  |
     |                  |
     --------------------        
               
     Region A = 32x32 caches, 1024 glyphs
     Region B = 32x64 caches, 512 glyphs
     Region C = 64x64 caches, 512 glyphs
     Region D = 128x128 caches, 256 glyphs

Region A is designed for small glyphs, Region B is for tall glyphs, Region C is for large glyphs, and Region D for huge glyphs. Glyphs are first rendered to an intermediate 2k x 512px R8 texture. This allows for minimum 4 Region D glyphs supersampled at 4 x 4 = 16x supersampling, and 8 Region C glyphs similarly. A simple 16-tap box downsample shader is then used to blit from this intermediate texture to the final atlas location.

The atlas texture looks something like this:

Usage

Pseudo-code demonstrating simple usage:

#define VE_FONTCACHE_IMPL
#include "../ve_fontcache.h"

static std::vector< uint8_t > buffer;
ve_fontcache_init( &cache );
ve_fontcache_configure_snap( &cache, width, height );
print_font = ve_fontcache_loadfile( &cache, "fonts/NotoSansJP-Light.otf", buffer, 19.0f );
ve_fontcache_draw_text( &cache, print_font, u8"hello world", 0, 0, 1.0f / width,  1.0f / height );

These header files need to be copied to your project:

ve_fontcache.h
utf8.h
stb_truetype.h

Except HarfBuzz, that's all the required dependencies. That said it's strongly recommended to use HarfBuzz ( TODO: HarfBuzz not supported yet, coming soon!! ) over the default utf8.h latin fallback text shaper.

Integration with rendering backend

VEFontCache is largely backend agnostic. Currently the demo project uses OpenGL 3.3 for Windows. That said it's designed to be integrated with VE, a Vulkan engine. Please read the "How to plug into rendering API" section in ve_fontcache.h for more documentation on how to implement your own backend to plumb this directly into your engine!

Screenshots

Similar projects and links

Here are links to some awesome similar and related projects:

• fontstash - https://github.com/memononen/fontstash
• stb_truetype ( has font rasterisation itself ) - https://github.com/nothings/stb/blob/master/stb_truetype.h
• slug - http://sluglibrary.com/
• pathfinder - https://github.com/pcwalton/pathfinder
• https://medium.com/@evanwallace/easy-scalable-text-rendering-on-the-gpu-c3f4d782c5ac