minimum-viable-game-engine/src/geometry.rs

use bytemuck::{Pod, Zeroable};
use nalgebra::Vector4;

#[repr(C)]
#[derive(Clone, Copy, Debug)]
pub struct Vertex {
    pos: [f32; 4],
    normal: [f32; 4],
    uv: [f32; 2],
}

impl Vertex {
    pub fn position(&self) -> Vector4<f32> {
        Vector4::new(self.pos[0], self.pos[1], self.pos[2], self.pos[3])
    }
    pub fn from(pos: [f32; 3], nor: [f32; 3], uv: [f32; 2]) -> Vertex {
        Vertex {
            pos: [pos[0], pos[1], pos[2], 1.0],
            normal: [nor[0], nor[1], nor[2], 0.0],
            uv: [0.0, 0.0],
        }
    }
}

unsafe impl Pod for Vertex {}
unsafe impl Zeroable for Vertex {}

#[derive(Clone, Debug)]
pub struct RawMesh {
    vertices: Vec<Vertex>,
    normals: Vec<[u32; 3]>,
}

pub fn load_obj(obj_path: &str, mtl_path: Option<&str>) -> (Vec<Vertex>, Vec<u32>) {

    let (models, materials) = tobj::load_obj(obj_path, true).expect("Failed to load file");

    println!("# of models: {}", models.len());
    println!("# of materials: {}", materials.len());


    let mut index_data: Vec<u32> = Vec::new();
    let mut vertex_data = Vec::new();

    for model in models {
        let mesh = &model.mesh;
        let mut next_face = 0;
        for f in 0..mesh.num_face_indices.len() {
            let end = next_face + mesh.num_face_indices[f] as usize;
            let face_indices: Vec<_> = mesh.indices[next_face..end].iter().collect();

            for i in face_indices {
                index_data.push(*i);
            }
            next_face = end;
        }

        assert!(mesh.positions.len() % 3 == 0);
        assert!(mesh.texcoords.len() % 2 == 0);

        for v in 0..mesh.positions.len() / 3 {
            let texcoords = if mesh.texcoords.len() == 0 {
                [0.0, 0.0]
            } else {
                [mesh.texcoords[2 * v], mesh.texcoords[2 * v + 1]]
            };

            vertex_data.push(Vertex::from(
                [
                    mesh.positions[3 * v],
                    mesh.positions[3 * v + 1],
                    mesh.positions[3 * v + 2],
                ],
                [
                    mesh.normals[3 * v],
                    mesh.normals[3 * v + 1],
                    mesh.normals[3 * v + 2],
                ],
                texcoords,
            ));
        }
    }
    (vertex_data.to_vec(), index_data.to_vec())
}