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use glam::{Vec2, Vec3, Vec3A};
pub fn generate_normals(index: &[[u32; 3]], position: &[Vec3]) -> Vec<Vec3> {
let mut normal_denom = vec![0; position.len()];
let mut normal = vec![Vec3::ZERO; position.len()];
for &[a, b, c] in index {
let pos_a = position[a as usize];
let pos_b = position[b as usize];
let pos_c = position[c as usize];
// TODO is this right?
let norm = (pos_b - pos_a).cross(pos_c - pos_a).normalize();
normal[a as usize] += norm;
normal[b as usize] += norm;
normal[c as usize] += norm;
normal_denom[a as usize] += 1;
normal_denom[b as usize] += 1;
normal_denom[c as usize] += 1;
}
for (denom, tang) in normal_denom.iter().zip(normal.iter_mut()) {
*tang /= *denom as f32;
}
normal
}
pub fn generate_tangents(index: &[[u32; 3]], position: &[Vec3], texcoord: &[Vec2]) -> Vec<Vec3> {
let mut tangent_denom = vec![0; position.len()];
let mut tangent = vec![Vec3::ZERO; position.len()];
for &[a, b, c] in index {
let (pos_a, uv_a) = (position[a as usize], texcoord[a as usize]);
let (pos_b, uv_b) = (position[b as usize], texcoord[b as usize]);
let (pos_c, uv_c) = (position[c as usize], texcoord[c as usize]);
let pd_ba = pos_b - pos_a;
let pd_ca = pos_c - pos_a;
let td_ba = uv_b - uv_a;
let td_ca = uv_c - uv_a;
let face_tangent =
(pd_ba * td_ca.y - pd_ca * td_ba.y) * (td_ba.x * td_ca.y - td_ba.y * td_ca.x);
tangent[a as usize] += face_tangent;
tangent[b as usize] += face_tangent;
tangent[c as usize] += face_tangent;
tangent_denom[a as usize] += 1;
tangent_denom[b as usize] += 1;
tangent_denom[c as usize] += 1;
}
for (denom, tang) in tangent_denom.iter().zip(tangent.iter_mut()) {
*tang /= *denom as f32;
}
tangent
}
pub fn generate_texcoords(index: &[[u32; 3]], position: &[Vec3A]) -> Vec<Vec2> {
let _ = (index, position);
// TODO implement equirectangular projection
todo!()
}
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