sepax2d

A safe Rust crate for finding and resolving collisions of convex shapes using the Separating Axis Theorem (SAT) in two dimensions.

Usage

Add the following to the [dependencies] section of your Cargo.toml:

sepax2d = "0.3"

Import the types of shapes you'd like to use and create some new shapes:

use sepax2d::prelude::*;

let rectangle = AABB::new(top_left, width, height);
let circle = Circle::new(center, radius);
let capsule = Capsule::new(center, arm, radius);

//The vertices of a polygon are position vectors
//relative to the shape's position, i.e. if position 
//is (1, 2), then the absolute location of the 
//first vertex is (1, 0).
let triangle = Polygon::from_vertices
(
    
    position,
    vec![(0.0, -2.0), (-1.0, 2.0), (1.0, 2.0)]

);

Use the sat_overlap(&left, &right) method to get a bool indicating whether or not the two given shapes overlap. Any struct implementing the Shape trait can be used.

assert!(sat_overlap(&circle, &capsule));
assert!(sat_overlap(&triangle, &rectangle));

Use the sat_collision(&left, &right) method to get a (f32, f32) which represents the shift needed to add to right's position in order to resolve the overlap of the two shapes.

let resolution = sat_overlap(&circle, &triangle);

let position = triangle.position();
triangle.set_position((position.0 + resolution.0, position.1 + resolution.1));

assert!(!sat_overlap(&circle, &triangle));

Use the contains_point(&shape, point) method to get a bool indicating whether or not the specified point is inside the given shape.

let rectangle = AABB::new((0.0, 0.0), 5.0, 2.0);

assert!(contains_point(&rect, (1.0, 1.0)));
assert!(!contains_point(&rect, (10.0, -1.0)));

Considerations

The Separating Axis Theorem only holds for convex shapes. If a concave shape is passed in, it is possible for overlap to be missed and false overlap to be detected.

Convexity is not a problem for Circle, AABB, or Capsule as those are convex by definition. For polygons, it is possible to define a concave shape. Polygon convexity can be tested using the polygon.is_convex() method. Alternatively, the Polygon::convex_from_vertices(position, vertices) constructor returns an Option(Polygon), which is None if you try to make a concave polygon.

Examples

The repository includes two example applications built with ggez which show off the overlap and collision functionality. They can be run from the repo via:

cargo run --example overlap

cargo run --example collision

Contribution

Please feel free to suggest additional features, bug fixes, or optimizations. Thanks!