cuboid.rs

use crate::{Indices, Mesh, MeshBuilder, Meshable, PrimitiveTopology};
use bevy_asset::RenderAssetUsages;
use bevy_math::{primitives::Cuboid, Vec3};
use bevy_reflect::prelude::*;

/// A builder used for creating a [`Mesh`] with a [`Cuboid`] shape.
#[derive(Clone, Copy, Debug, Reflect)]
#[reflect(Default, Debug, Clone)]
pub struct CuboidMeshBuilder {
    half_size: Vec3,
}

impl Default for CuboidMeshBuilder {
    /// Returns the default [`CuboidMeshBuilder`] with a width, height, and depth of `1.0`.
    fn default() -> Self {
        Self {
            half_size: Vec3::splat(0.5),
        }
    }
}

impl MeshBuilder for CuboidMeshBuilder {
    fn build(&self) -> Mesh {
        let min = -self.half_size;
        let max = self.half_size;

        // Suppose Y-up right hand, and camera look from +Z to -Z
        let vertices = &[
            // Front
            ([min.x, min.y, max.z], [0.0, 0.0, 1.0], [0.0, 0.0]),
            ([max.x, min.y, max.z], [0.0, 0.0, 1.0], [1.0, 0.0]),
            ([max.x, max.y, max.z], [0.0, 0.0, 1.0], [1.0, 1.0]),
            ([min.x, max.y, max.z], [0.0, 0.0, 1.0], [0.0, 1.0]),
            // Back
            ([min.x, max.y, min.z], [0.0, 0.0, -1.0], [1.0, 0.0]),
            ([max.x, max.y, min.z], [0.0, 0.0, -1.0], [0.0, 0.0]),
            ([max.x, min.y, min.z], [0.0, 0.0, -1.0], [0.0, 1.0]),
            ([min.x, min.y, min.z], [0.0, 0.0, -1.0], [1.0, 1.0]),
            // Right
            ([max.x, min.y, min.z], [1.0, 0.0, 0.0], [0.0, 0.0]),
            ([max.x, max.y, min.z], [1.0, 0.0, 0.0], [1.0, 0.0]),
            ([max.x, max.y, max.z], [1.0, 0.0, 0.0], [1.0, 1.0]),
            ([max.x, min.y, max.z], [1.0, 0.0, 0.0], [0.0, 1.0]),
            // Left
            ([min.x, min.y, max.z], [-1.0, 0.0, 0.0], [1.0, 0.0]),
            ([min.x, max.y, max.z], [-1.0, 0.0, 0.0], [0.0, 0.0]),
            ([min.x, max.y, min.z], [-1.0, 0.0, 0.0], [0.0, 1.0]),
            ([min.x, min.y, min.z], [-1.0, 0.0, 0.0], [1.0, 1.0]),
            // Top
            ([max.x, max.y, min.z], [0.0, 1.0, 0.0], [1.0, 0.0]),
            ([min.x, max.y, min.z], [0.0, 1.0, 0.0], [0.0, 0.0]),
            ([min.x, max.y, max.z], [0.0, 1.0, 0.0], [0.0, 1.0]),
            ([max.x, max.y, max.z], [0.0, 1.0, 0.0], [1.0, 1.0]),
            // Bottom
            ([max.x, min.y, max.z], [0.0, -1.0, 0.0], [0.0, 0.0]),
            ([min.x, min.y, max.z], [0.0, -1.0, 0.0], [1.0, 0.0]),
            ([min.x, min.y, min.z], [0.0, -1.0, 0.0], [1.0, 1.0]),
            ([max.x, min.y, min.z], [0.0, -1.0, 0.0], [0.0, 1.0]),
        ];

        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 indices = Indices::U32(vec![
            0, 1, 2, 2, 3, 0, // front
            4, 5, 6, 6, 7, 4, // back
            8, 9, 10, 10, 11, 8, // right
            12, 13, 14, 14, 15, 12, // left
            16, 17, 18, 18, 19, 16, // top
            20, 21, 22, 22, 23, 20, // bottom
        ]);

        Mesh::new(
            PrimitiveTopology::TriangleList,
            RenderAssetUsages::default(),
        )
        .with_inserted_attribute(Mesh::ATTRIBUTE_POSITION, positions)
        .with_inserted_attribute(Mesh::ATTRIBUTE_NORMAL, normals)
        .with_inserted_attribute(Mesh::ATTRIBUTE_UV_0, uvs)
        .with_inserted_indices(indices)
    }
}

impl Meshable for Cuboid {
    type Output = CuboidMeshBuilder;

    fn mesh(&self) -> Self::Output {
        CuboidMeshBuilder {
            half_size: self.half_size,
        }
    }
}

impl From<Cuboid> for Mesh {
    fn from(cuboid: Cuboid) -> Self {
        cuboid.mesh().build()
    }
}