# harfbuzz_rs_now
[](https://crates.io/crates/harfbuzz_rs_now)
[](https://docs.rs/harfbuzz_rs_now)
[](https://github.com/KonghaYao/harfbuzz_rs_now/actions/workflows/rust.yml)
`harfbuzz_rs_now` is a high-level interface to HarfBuzz, exposing its most important functionality in a safe manner using Rust. And we provide more powerful methods to you.
- [x] normal usage
- [x] subset font
- [x] svg string output
# What is HarfBuzz?
HarfBuzz is a library for performing complex text layout. It does not perform
any drawing. This is quite a low-level operation. If you want to simply draw
some text on the screen you should maybe choose another more high-level library.
However if you want to build a library for drawing text on some canvas or need a
lot of control on advanced text layout then this is the right library to use.
# Getting Started
To shape a simple string of text you just create a `Font` from a font file, fill
a `Buffer` with some text and call the `shape` function.
```rust
use harfbuzz_rs_now::*;
fn main() {
let path = "./src/SourceSansVariable-Roman.ttf";
let index = 0; //< face index in the font file
let face = Face::from_file(path, index).unwrap();
let mut font = Font::new(face);
let buffer = UnicodeBuffer::new().add_str("Hello World!");
let output = shape(&font, buffer, &[]);
// The results of the shaping operation are stored in the `output` buffer.
let positions = output.get_glyph_positions();
let infos = output.get_glyph_infos();
// iterate over the shaped glyphs
for (position, info) in positions.iter().zip(infos) {
let gid = info.codepoint;
let cluster = info.cluster;
let x_advance = position.x_advance;
let x_offset = position.x_offset;
let y_offset = position.y_offset;
// Here you would usually draw the glyphs.
println!(
"gid{:?}={:?}@{:?},{:?}+{:?}",
gid, cluster, x_advance, x_offset, y_offset
);
}
// render a simple string to svg!
let svg_string = font.render_svg_text("Hello World\nI can see you", &[]);
// create a font subset
let font_subset = subset::Subset::new();
font_subset.clear_drop_table(); // I want to keep all table inside this font
font_subset.adjust_layout(); // I want to keep all feature and script layout
let new_font_face = font_subset.run_subset(&face);
let binary_data_of_subset = new_font_face.face_data().get_data();
}
```
This should print out something similar to the following:
```text
gid41=0@741,0+0
gid70=1@421,0+0
gid77=2@258,0+0
gid77=3@253,0+0
gid80=4@510,0+0
gid1=5@227,0+0
gid56=6@874,0+0
gid80=7@498,0+0
gid83=8@367,0+0
gid77=9@253,0+0
gid69=10@528,0+0
gid2=11@276,0+0
```
The values of `x_advance`, `x_offset`, `y_advance` and `y_offset` are all given in so-called _font units_ by default.
By calling `face.upem()` you get the number of font units per [EM](<https://en.wikipedia.org/wiki/Em_(typography)>) for
a specific `face`. This `upem` value can be used to scale the advances and offsets to a given font-size.
For example, if you want to display a font at 16 point (pt) size, that means that _1 EM = 16 pt_.
In this example, to convert a value, say `x_advance`, from font-units to points, we compute `((x_advance * font_size) as f64) / (upem as f64)`, where `font_size = 16` is a variable specifying the font size in points.
Note that harfbuzz internally supports scaling fonts itself as well (using `font.set_scale(...)`, etc.) but in my opinion it is easier to scale the results oneself as described in the paragraph above.
# Supported HarfBuzz versions
This crate is tested to work with harfbuzz versions 2.0 and higher. Older versions may work as well. I recommend statically linking the harfbuzz library provided by the `harfbuzz-sys` crate which is always up-to-date.
# Optional Features
If you want to use rusttype as font functions enable the `rusttype` feature.