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use smallvec::smallvec;

use crate::{
    mesh::{CpuMesh, Material, MeshError},
    CpuModel, RenderContext, Rgba32Unmul,
};

#[derive(thiserror::Error, Debug)]
pub enum ObjImportError {
    #[error(transparent)]
    ObjLoading(#[from] tobj::LoadError),

    #[error(transparent)]
    Mesh(#[from] MeshError),
}

/// Load a [Wavefront .obj file](https://en.wikipedia.org/wiki/Wavefront_.obj_file)
/// into the mesh & texture manager.
pub fn load_obj_from_buffer(
    buffer: &[u8],
    ctx: &RenderContext,
) -> Result<CpuModel, ObjImportError> {
    re_tracing::profile_function!();

    let (models, _materials) = tobj::load_obj_buf(
        &mut std::io::Cursor::new(buffer),
        &tobj::LoadOptions {
            single_index: true,
            triangulate: true,
            ..Default::default()
        },
        |_material_path| Err(tobj::LoadError::MaterialParseError),
    )?;

    // TODO(andreas) Merge all obj meshes into a single re_renderer mesh with multiple materials.
    let mut model = CpuModel::default();
    for obj_model in models {
        // This could be optimized by using bytemuck.

        let mesh = obj_model.mesh;
        let vertex_positions: Vec<glam::Vec3> = mesh
            .positions
            .chunks_exact(3)
            .map(|p| glam::vec3(p[0], p[1], p[2]))
            .collect();

        let triangle_indices = mesh
            .indices
            .chunks_exact(3)
            .map(|p| glam::uvec3(p[0], p[1], p[2]))
            .collect();

        let mut vertex_colors: Vec<Rgba32Unmul> = mesh
            .vertex_color
            .chunks_exact(3)
            .map(|c| {
                Rgba32Unmul::from_rgb(
                    // It is not specified if the color is in linear or gamma space, but gamma seems a safe bet.
                    (c[0] * 255.0).round() as u8,
                    (c[1] * 255.0).round() as u8,
                    (c[2] * 255.0).round() as u8,
                )
            })
            .collect();
        vertex_colors.resize(vertex_positions.len(), Rgba32Unmul::WHITE);

        let mut vertex_normals: Vec<glam::Vec3> = mesh
            .normals
            .chunks_exact(3)
            .map(|n| glam::vec3(n[0], n[1], n[2]))
            .collect();
        vertex_normals.resize(vertex_positions.len(), glam::Vec3::ZERO);

        let mut vertex_texcoords: Vec<glam::Vec2> = mesh
            .texcoords
            .chunks_exact(2)
            .map(|t| glam::vec2(t[0], t[1]))
            .collect();
        vertex_texcoords.resize(vertex_positions.len(), glam::Vec2::ZERO);

        let texture = ctx.texture_manager_2d.white_texture_unorm_handle();

        let mesh = CpuMesh {
            label: obj_model.name.into(),
            triangle_indices,
            vertex_positions,
            vertex_colors,
            vertex_normals,
            vertex_texcoords,

            // TODO(andreas): proper material loading
            materials: smallvec![Material {
                label: "default material".into(),
                index_range: 0..mesh.indices.len() as u32,
                albedo: texture.clone(),
                albedo_factor: crate::Rgba::WHITE,
            }],
        };

        mesh.sanity_check()?;
        model.add_single_instance_mesh(mesh);
    }

    Ok(model)
}