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115 lines
4.3 KiB
Markdown
115 lines
4.3 KiB
Markdown
# Notice
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This is the original readme fo the C++ implementation by Xi Chen.
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# VE Font Cache is a single header-only GPU font rendering library designed for game engines.
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It aims to:
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* Be fast and simple to integrate.
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* Take advantage of modern GPU power.
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* Be backend agnostic and easy to port to any API such as Vulkan, DirectX, OpenGL.
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* Load TTF & OTF file formats directly.
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* Use only runtime cache with no offline calculation.
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* Render glyphs at reasonable quality at a wide range of font sizes.
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* Support a good amount of internationalisation. そうですね!
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* Support cached text shaping with HarfBuzz with simple Latin-style fallback.
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* Load and unload fonts at any time.
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# How it works
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Glyphs are GPU rasterised with 16x supersampling. This method is a simplification of "Easy Scalable Text Rendering on the GPU",
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by Evan Wallace, making use of XOR blending. Bézier curves are handled via brute force triangle tessellation; even 6 triangles per
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curve only generates < 300 triangles, which is nothing for modern GPUs! This avoids complex frag shader for reasonable quality.
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Texture atlas caching uses naïve grid placement; this wastes a lot of space but ensures interchangeable cache slots allowing for
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straight up LRU ( Least Recently Used ) caching scheme to be employed.
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The font atlas is a single 4k x 2k R8 texture divided into 4 regions:
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```
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2k
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--------------------
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| | |
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| A | |
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| | | 2
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|---------| C | k
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| | |
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1k | B | |
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| | |
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--------------------
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| | 2
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| D | k
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--------------------
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Region A = 32x32 caches, 1024 glyphs
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Region B = 32x64 caches, 512 glyphs
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Region C = 64x64 caches, 512 glyphs
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Region D = 128x128 caches, 256 glyphs
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```
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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.
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Glyphs are first rendered to an intermediate 2k x 512px R8 texture. This allows for minimum 4 Region D glyphs supersampled at
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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
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intermediate texture to the final atlas location.
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The atlas texture looks something like this:
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# Usage
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Pseudo-code demonstrating simple usage:
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```cpp
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#define VE_FONTCACHE_IMPL
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#include "../ve_fontcache.h"
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static std::vector< uint8_t > buffer;
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ve_fontcache_init( &cache );
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ve_fontcache_configure_snap( &cache, width, height );
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print_font = ve_fontcache_loadfile( &cache, "fonts/NotoSansJP-Light.otf", buffer, 19.0f );
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ve_fontcache_draw_text( &cache, print_font, u8"hello world", 0, 0, 1.0f / width, 1.0f / height );
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```
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These header files need to be copied to your project:
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```
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ve_fontcache.h
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utf8.h
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stb_truetype.h
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```
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Except HarfBuzz, that's all the required dependencies. That said it's strongly recommended
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to use HarfBuzz ( TODO: HarfBuzz not supported yet, coming soon!! ) over the default utf8.h latin
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fallback text shaper.
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## Integration with rendering backend
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VEFontCache is largely backend agnostic. Currently the demo project uses OpenGL 3.3 for Windows.
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That said it's designed to be integrated with VE, a Vulkan engine.
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Please read the "How to plug into rendering API" section in ve_fontcache.h for more documentation
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on how to implement your own backend to plumb this directly into your engine!
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# Screenshots
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# Similar projects and links
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Here are links to some awesome similar and related projects:
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* fontstash - https://github.com/memononen/fontstash
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* stb_truetype ( has font rasterisation itself ) - https://github.com/nothings/stb/blob/master/stb_truetype.h
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* slug - http://sluglibrary.com/
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* pathfinder - https://github.com/pcwalton/pathfinder
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* https://medium.com/@evanwallace/easy-scalable-text-rendering-on-the-gpu-c3f4d782c5ac
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