GPU-based 2D graphics rendering tools in Rust using path tessellation.

Crates

This meta-crate (lyon) reexports the following sub-crates for convenience:

• - lyon_tessellation - Path tessellation routines.
• - lyon_path - Tools to build and iterate over paths.
• - lyon_algorithms - Various 2d path related algorithms.
• - lyon_geom - 2d utilities for cubic and quadratic bézier curves, arcs and more.
• - lyon_svg - Create paths using SVG's path syntax.
• - lyon_extra - Additional testing and debugging tools.
• - lyon_tess2 - Alternative fill tessellation implementation using libtess2.

Each lyon_<name> crate is reexported as a <name> module in lyon. For example:

extern crate lyon_tessellation;
use lyon_tessellation::FillTessellator;

Is equivalent to:

extern crate lyon;
use lyon::tessellation::FillTessellator;

Feature flags

serialization using serde can be enabled on each crate using the serialization feature flag (disabled by default).

When using the main crate lyon, the lyon_svg, lyon_tess2 and lyon_extra dependencies are disabled by default. They can be added with the feature flags svg, tess2 and extra.

Additional documentation and links

• wgpu example.
• wgpu_svg example similar to the first example, can render a very small subset of SVG.
• There is some useful documentation on the project's wiki.
• The source code is available on the project's git repository.
• Interested in contributing? Pull requests are welcome. If you would like to help but don't know what to do specifically, have a look at the github issues, some of which are tagged as easy.

Examples

Tessellating a rounded rectangle

The lyon_tessellation crate provides a collection of tessellation routines for common shapes such as rectangles and circles. Let's have a look at how to obtain the fill tessellation a rectangle with rounded corners:

use lyon::math::{rect, Point};
use lyon::path::{builder::*, Winding};
use lyon::tessellation::{FillTessellator, FillOptions, VertexBuffers};
use lyon::tessellation::geometry_builder::simple_builder;

fn main() {
let mut geometry: VertexBuffers<Point, u16> = VertexBuffers::new();
let mut geometry_builder = simple_builder(&mut geometry);
let options = FillOptions::tolerance(0.1);
let mut tessellator = FillTessellator::new();

let mut builder = tessellator.builder(
&options,
&mut geometry_builder,
);

builder.add_rounded_rectangle(
&rect(0.0, 0.0, 100.0, 50.0),
&BorderRadii {
top_left: 10.0,
top_right: 5.0,
bottom_left: 20.0,
bottom_right: 25.0,
},
Winding::Positive
);

builder.build();

// The tessellated geometry is ready to be uploaded to the GPU.
println!(" -- {} vertices {} indices",
geometry.vertices.len(),
geometry.indices.len()
);
}

Building and tessellating an arbitrary path

extern crate lyon;
use lyon::math::{point, Point};
use lyon::path::Path;
use lyon::path::builder::*;
use lyon::tessellation::*;

fn main() {
// Build a Path.
let mut builder = Path::builder();
builder.begin(point(0.0, 0.0));
builder.line_to(point(1.0, 0.0));
builder.quadratic_bezier_to(point(2.0, 0.0), point(2.0, 1.0));
builder.cubic_bezier_to(point(1.0, 1.0), point(0.0, 1.0), point(0.0, 0.0));
builder.close();
let path = builder.build();

// Let's use our own custom vertex type instead of the default one.
#[derive(Copy, Clone, Debug)]
struct MyVertex { position: [f32; 2] };

// Will contain the result of the tessellation.
let mut geometry: VertexBuffers<MyVertex, u16> = VertexBuffers::new();

let mut tessellator = FillTessellator::new();

{
// Compute the tessellation.
tessellator.tessellate_path(
&path,
&FillOptions::default(),
&mut BuffersBuilder::new(&mut geometry, |vertex: FillVertex| {
MyVertex {
position: vertex.position().to_array(),
}
}),
).unwrap();
}

// The tessellated geometry is ready to be uploaded to the GPU.
println!(" -- {} vertices {} indices",
geometry.vertices.len(),
geometry.indices.len()
);
}

What is the tolerance variable in these examples?

The tessellator operates on flattened paths (that only contains line segments) so we have to approximate the curves segments with sequences of line segments. To do so we pick a tolerance threshold which is the maximum distance allowed between the curve and its approximation. The documentation of the lyon_geom crate provides more detailed explanations about this tolerance parameter.

Rendering the tessellated geometry

Lyon does not provide with any GPU abstraction or rendering backend (for now). It is up to the user of this crate to decide whether to use OpenGL, vulkan, gfx-rs, wgpu, glium, or any low level graphics API and how to render it. The wgpu example can be used to get an idea of how to render the geometry (in this case using wgpu).