fauntlet - the font gauntlet

A tool to compare the output of Skrifa and FreeType.

Capabilities

This currently compares glyph outlines (in path form) and advance widths for fixed sets of sizes and locations in variation space. Prior to comparison, the outlines are “regularized” to account for minor differences in output. These differences do not affect rendering and exist for the following reasons:

1. All contours are implicitly closed in FreeType. Skrifa emits close elements to allow our output to be further processed by, e.g. a stroke converter without requiring modification.
2. The FreeType CFF loader drops degenerate move and line elements but does so before a final scaling step which may produce additional unused path commands. Skrifa performs this filtering step after all scaling steps have been applied, leading to more aggressive removal of degenerates.
3. In unscaled (FT_LOAD_NO_SCALE) mode, the FreeType TrueType loader yields outlines with coordinates in integral font units. Passing these to FT_Outline_Decompose results in truncated coordinates for some implicit oncurve points (those with odd deltas in either direction). Skrifa produces fractional values for these midpoints.

Usage

To compare glyphs for a single font:

cargo run --release -p fauntlet -- compare-glyphs path/to/font.ttf

You can specify multiple font files and each file may use glob syntax. For example:

cargo run --release -p fauntlet -- compare-glyphs /myfonts/noto/**/hinted/**.ttf otherfonts/*.?tf

This will process all fonts in parallel, emitting diagnostics to stderr if mismatches are found. Use the --exit-on-fail flag to end the process on the first failure.