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Toy CPU and GPU implementations of the Slug rendering algorithm
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UNLICENSE.MD initial commit Apr 9, 2019



This is a toy/experimental project showing off how to get started rendering glyphs with Eric Lengyel's Slug algorithm on both CPUs and GPUs.

I recommend reading at least the slides linked in the reference section before any of the code.


  • Windows x64
  • Visual C++ 2013 or later for compiling
  • OpenGL 3.2 for the hardware renderer

Project breakdown

Sub-project Purpose
Font generator Reads a .ttf TrueType font file and outputs a .sluggish file
Software renderer Reads a .sluggish file and outputs a .tga image per specified code point
Hardware renderer Reads a .sluggish file and renders up to 6 specified glyphs using OpenGL
Feature Support
Curves texture (FP32) YES
Bands texture (U16) YES
Cutting glyphs into bands (performance) YES
Sorting curves (performance) YES
High-quality implementation of anything NO
High performance NO
16-bit floating point encoding NO
Data de-duplication and compression NO
Text layouting NO
Colored shapes NO
Adaptive super-sampling NO
Gamma correction NO
Bounding polygons NO

The goal was to keep things pretty simple while still not having awful performance. For instance, cutting the glyphs into bands has been implemented because it's simple and improves performance massively.


By default, the debugger's target executable isn't in the output directory but a directory path specified by the SLUGGISH_APP_DIR environment variable.

The .exe and .pdb files are copied over to that directory after every build.

To make this process easy, you can launch Visual Studio through a simple batch script:

:: This file would sit next to the Sluggish directory
cd Sluggish\makefiles\vs2013
set SLUGGISH_APP_DIR=C:\important_stuff\sluggish


To learn more about how the Slug algorithm works, refer to:
GPU-Centered Font Rendering Directly from Glyph Outlines by Eric Lengyel
Journal of Computer Graphics Techniques (JCGT), vol. 6, no. 2, 31-47, 2017


Project/File License(s) License File(s)
This project Unlicense (public domain) UNLICENSE.MD
SDL 2 zlib libs/SDL2/COPYING.txt
GLEW Modified BSD License
Mesa 3-D License (MIT)
Khronos License (MIT)
premake 5 premake 5 makefiles/PREMAKE_LICENSE.txt
stb_truetype.h Pick-a-license:
Unlicense (public domain)
stb_image_write.h Pick-a-license:
Unlicense (public domain)


While there is no patent on the Slug algorithm as of the time of writing, Eric Lengyel has made an application for one and the process is still on-going...

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