Learn to scan Google Fonts for fonts that support a given codepoint.
It is assumed that all code is cloned into the same directory and that cargo new is run in that directory.
At times only partial commandline output is given to reduce noise.
See https://www.rust-lang.org/tools/install
If you haven’t written Rust at all so far take the time to complete at least one of:
VSCode with rust-analyzer is a good default if you don’t already have a favorite.
Clone https://github.com/google/fonts
Let’s write a program! We’ll make a command line tool for now.
# Create a new binary project
$ cargo new melting_face_finder
Created binary (application) `melting_face_finder` package
$ cd melting_face_finder/
$ tree
.
├── Cargo.toml
└── src
└── main.rs
2 directories, 2 files
$ cargo run
Hello, world!
Cargo.toml is your manifest. It configures your package name, dependencies, license, and more.
This isn’t a serious program. When you encounter a Result or Option feel free to call use unwrap or expect. This will cause a panic if it fails. That’s fine for exploration, it’ll make things go much faster.
First off, scan your copy of Google Fonts (cloned above) to find font files. Let’s say those are files names *.ttf and *.otf. glob is good at this sort of thing, let’s add a dependency!
$ cargo add glob
Updating crates.io index
Adding glob v0.3.1 to dependencies.
Updating crates.io index
$ cat Cargo.toml
[package]
name = "melting_face_finder"
version = "0.1.0"
edition = "2021"
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
[dependencies]
glob = "0.3.1"
Glob should find you quite a lot of font files. If scanning them all is slow you could narrow things to ../fonts/ofl/noto*/*.ttf.
Print what you find using println!. Hint:
{:?} to print the Debug representation.Stuck? See 1-glob.rs.
https://unicode.org/Public/emoji/15.1/emoji-test.txt says 0x1FAE0 is melting face and that’s just what we need. But … which fonts support it?!
Let’s use Skrifa to query our fonts cmap. Add a dependency!
$ cargo add skrifa
Updating crates.io index
Adding skrifa v0.16.0 to dependencies.
Updating crates.io index
$ cat Cargo.toml
[package]
name = "melting_face_finder"
version = "0.1.0"
edition = "2021"
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
[dependencies]
glob = "0.3.1"
skrifa = "0.16.0"
Next up, after we find each font let’s load the bytes into memory. std::fs::read
should help. Just to confirm it’s working maybe print the number of bytes for each path?
Stuck? See 2-bytes.rs.
Now it gets a little tricky. We need to load the bytes as a FontRef, passing a reference to our bytes to the constructor. Note that FontRef does not take ownership over those bytes. You can ignore that for now if you want.
To find out what codepoints are supported we need a Charmap. Those are obtained from the MetadataProvider. But … we’ve got a FontRef, where do we get a MetadataProvider?! Well, if you squint hard at FontRef you should see two interesting clues:
FontRef is a Table Provider and all Table Providers are MetadataProviders. Traits are fun, why not read about Traits? Oh right, we have an actual job to do!
We need to import some things. It’s easiest by using an IDE, in VSCode just type let charmap = font.ch and you should get a list of options, one of which is charmap() (use skrifa::MetadataProvider). Press Enter and it should add MetadataProvider to the things you are importing from Skrifa, probably by modifying the use at the top of your program to use skrifa::{FontRef, MetadataProvider};.
Now we’ve got a charmap we can at last query our font to see if it calims to support melting face using the map method. Hint: you might need to make a literal for 0x1FAE0 that is explicitly u32. See integer literal expressions. In general, Rust wants you to be a lot more explicit about types than you might be used to.
And … we’re done!
$ cargo run | grep true
"../fonts/ofl/notocoloremoji/NotoColorEmoji-Regular.ttf" supports melting face? true
"../fonts/ofl/notocoloremojicompattest/NotoColorEmojiCompatTest-Regular.ttf" supports melting face? true
"../fonts/ofl/notoemoji/NotoEmoji[wght].ttf" supports melting face? true
Stuck? See 3-charmap.rs.