Bevy 0.11 single 2D line segment mesh

line_segment.rs

// License: Apache-2.0 / MIT

// Note: this is not a good strategy for performance if you need a lot of these things.
// Consider using rotated sprites which Bevy is heavily optimized for, or its "line gizmos."

use bevy::{
    prelude::*,
    render::{mesh::Indices, render_resource::PrimitiveTopology},
    sprite::MaterialMesh2dBundle,
};

pub struct LineSegment {
    pub start: Vec2,
    pub end: Vec2,
    pub thickness: f32,
}

impl From<LineSegment> for Mesh {
    fn from(segment: LineSegment) -> Self {
        let LineSegment {
            start,
            end,
            thickness,
        } = segment;

        let dir = (start - end).normalize();
        let perp = Vec2::new(-dir.y, dir.x);

        let s1 = start + perp * -thickness;
        let s2 = start + perp * thickness;
        let e1 = end + perp * -thickness;
        let e2 = end + perp * thickness;

        let vertices = [
            ([s1.x, s1.y, 0.0], [0.0, 0.0, 1.0], [0.0, 1.0]),
            ([s2.x, s2.y, 0.0], [0.0, 0.0, 1.0], [0.0, 0.0]),
            ([e1.x, e1.y, 0.0], [0.0, 0.0, 1.0], [1.0, 0.0]),
            ([e2.x, e2.y, 0.0], [0.0, 0.0, 1.0], [1.0, 1.0]),
        ];

        let indices = Indices::U32(vec![0, 1, 2, 1, 3, 2]);

        let positions: Vec<_> = vertices.iter().map(|(p, _, _)| *p).collect();
        let normals: Vec<_> = vertices.iter().map(|(_, n, _)| *n).collect();
        let uvs: Vec<_> = vertices.iter().map(|(_, _, uv)| *uv).collect();

        let mut mesh = Mesh::new(PrimitiveTopology::TriangleList);
        mesh.set_indices(Some(indices));
        mesh.insert_attribute(Mesh::ATTRIBUTE_POSITION, positions);
        mesh.insert_attribute(Mesh::ATTRIBUTE_NORMAL, normals);
        mesh.insert_attribute(Mesh::ATTRIBUTE_UV_0, uvs);
        mesh
    }
}

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .run();
}

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<ColorMaterial>>,
) {
    commands.spawn(Camera2dBundle::default());

    commands.spawn(MaterialMesh2dBundle {
        mesh: meshes
            .add(Mesh::from(LineSegment {
                start: Vec2::new(0., 0.),
                end: Vec2::new(100., 100.),
                thickness: 2.0,
            }))
            .into(),
        material: materials.add(ColorMaterial::from(Color::PURPLE)),
        ..default()
    });
}