A Decade of Slug: GPU Font Rendering Algorithm
Source: terathon.com by Eric Lengyel | March 17, 2026
What is Slug?
Slug is a groundbreaking algorithm for rendering fonts directly from Bézier curves on the GPU without texture maps. Developed in Fall 2016, it celebrates its 10th anniversary in 2026.
Key Highlights
- Licensed by: Activision, Blizzard, id Software, 2K Games, Ubisoft, Warner Brothers, Insomniac, Zenimax, Adobe, and many more
- Used in: Video games, scientific visualization, CAD, video editing, medical equipment, planetariums
- Core Innovation: Direct rendering from Bézier curves - no precomputed textures needed
- Robustness: Zero artifacts (dropped pixels, sparkles, or streaks) through precise winding number calculations
Dynamic Dilation - The Major Update
The biggest improvement since 2017 is "dynamic dilation" - automatically calculating the optimal bounding polygon expansion for each glyph based on the model-view-projection matrix and viewport dimensions.
Before: Users had to manually specify a constant dilation distance, which was either too small (causing aliasing) or too large (wasting performance).
After: The algorithm automatically calculates the perfect dilation distance in the vertex shader for every render, ensuring optimal quality and performance at any scale.
Patent Announcement
Effective March 17, 2026, Eric Lengyel has permanently dedicated the Slug patent (US10373352B1) to the public domain. Anyone can freely implement the Slug algorithm without a license.
Resources
Why This Matters
This is a significant contribution to the graphics programming community. The algorithm enables high-quality, anti-aliased text rendering at any scale and angle, with mathematical guarantees of robustness. The patent dedication ensures this technology will benefit everyone.