x/image: packages to render TrueType fonts

[nigeltao]

github.com/golang/freetype already exists, but its license (the Freetype license) differs from the Go standard library, and code in the stdlib or under golang.org/x cannot depend on out-of-tree code.

I propose to add two new packages in the golang.org/x/image repo that together lets you use TTFs to draw text. There are existing packages under golang.org/x/image/font that can draw bitmap fonts, but this would be the first golang.org/x package that draws vector fonts.

The golang.org/x/image/vector package rasterizes 2-D vector graphics: filled and stroked polygons and Bézier curves. 2-D vector graphics (and the scope of this package) encompasses more than just fonts, but this package will rasterize the glyphs of a vector font such as TrueType. It'd be comparable to the github.com/golang/freetype/raster package, but not based on the Freetype code.

The golang.org/x/image/font/sfnt package parses sfnt font formats, including TrueType (.ttf) and OpenType (.otf). It will implement the existing golang.org/x/image/font font.Face interface for font format agnostic text drawing. It'd be comparable to the github.com/golang/freetype/truetype package, but not based on the Freetype code.

A proof of concept (as a single "package main" instead of two separate packages) exists in a separate repository, https://github.com/google/font-go, which is in turn based on https://github.com/google/font-rs and the accompanying article (https://medium.com/@raphlinus/inside-the-fastest-font-renderer-in-the-world-75ae5270c445) by Raph Levien of Google. Roughly speaking, font.go would become package sfnt, and raster.go and acc*.{go,s} would become package vector.

[adg]

I'm @adg and I approve this proposal.

[bradfitz]

I'm not @adg and I approve this proposal.

[gopherbot]

CL https://golang.org/cl/28347 mentions this issue.

[akavel]

Is the reference API of the Rust package published somewhere, or does one have to browse the sources? Will it be possible to stroke curves with dashes/dots pattern? (I use forked freetype-go to draw dashed lines and curves in my Go port of ditaa.)

[nigeltao]

I don't know enough about the Rust community to know if the API is published anywhere other than the source at https://github.com/google/font-rs but its API is pretty minimal: it is a prototype / proof of concept rather than a polished library.

I expect golang.org/x/image/vector will be as capable as github.com/golang/freetype/raster in terms of strokes, so you can build your own dashing code on top of that.

[gopherbot]

CL https://golang.org/cl/33417 mentions this issue.