VarFont

VarFont is an innovative solution designed for re-rasterization-free variable-font morphing, utilizing a technique known as knot-lattice multilinear blending. This repository allows developers and researchers to significantly enhance rendering performance when manipulating variable fonts.

Key Features

• Speed: Achieve approximately 3× faster axis drags, with rendering times reaching 0.23 µs per glyph for the 13-axis Roboto Flex, compared to 0.71 µs for FreeType re-instancing.
• Efficiency: Experience a reduction of 4× fewer re-rasterizations per drag. With only 0.24 cell rebuilds per glyph, this method eliminates the need for full re-instancing each frame, allowing the glyph atlas to remain valid throughout the rendering process.
• Accuracy: Maintain high fidelity with a maximum outline error of 0.25% em and a mean per-pixel coverage error of 0.08%, closely matching the performance of FreeType.

Important Consideration

It’s noteworthy that this technique does not perform grid-fitting (hinting). Therefore, it does not provide speed advantages at smaller text sizes where hinted rendering is crucial.

Project Structure

The VarFont repository contains:

• Academic Manuscript: Detailed documentation, including figures and citations, can be found in the paper directory. Access the full paper here.
• Engine Snapshot: The vendored engine snapshot is available in the lib/imvarfont/ directory.
• Research Tools: Tools like morph_probe and benchmarks are located in the research/ directory, which provides multiple resources for validation.
• Documentation: Additional implementation notes and benchmarks can be found in the docs/ directory.

Quick Start Guide

To generate paper documentation or run validations and benchmarks, the following commands can be executed:

# Generate Paper PDF (requires pandoc + tectonic)  
make -C paper

# Run Validation / Benchmarks  
cmake -B build -DCMAKE_BUILD_TYPE=Release  
cmake --build build --target morph_probe bench

Explore how VarFont can optimize your variable-font implementations and improve rendering performance in applications. Further insights and the underlying technology principles are substantiated through the academic manuscript provided.