95 lines
2.9 KiB
Rust
95 lines
2.9 KiB
Rust
|
use bevy::prelude::*;
|
||
|
|
use bevy::math::Mat4;
|
||
|
|
|
||
|
|
/// creates a conventional projection matrix from frustum planes
|
||
|
|
///
|
||
|
|
/// returns a potentially off-axis projection matrix
|
||
|
|
pub fn make_projection_rh_from_frustum(left: f32, right: f32, bottom: f32, top: f32, near:f32, far:f32) -> Mat4
|
||
|
|
{
|
||
|
|
// based on OpenSceneGraph / glFrustum implementation
|
||
|
|
let a = (right + left) / (right - left);
|
||
|
|
let b: f32 = (top + bottom) / (top - bottom);
|
||
|
|
let c= if far.abs() > f32::MAX { -1.0 } else { -(far + near) / (far - near)};
|
||
|
|
let d = if far.abs() > f32::MAX { -2.0 * near } else { -2.0 * far * near / (far - near) };
|
||
|
|
|
||
|
|
Mat4::from_cols(
|
||
|
|
Vec4::new(2.0 * near / (right-left),0.0,0.0,0.0),
|
||
|
|
Vec4::new(0.0, 2.0 *near / (top-bottom), 0.0,0.0),
|
||
|
|
Vec4::new(a, b, c, -1.0),
|
||
|
|
Vec4::new(0.0, 0.0, d, 0.0))
|
||
|
|
}
|
||
|
|
|
||
|
|
|
||
|
|
/// creates a projection from a frustum planes with a reversed depth mapped to [0..1]
|
||
|
|
pub fn make_projection_rh_from_frustum_reversed(left: f32, right: f32, bottom: f32, top: f32, z_near:f32, z_far:f32) -> Mat4
|
||
|
|
{
|
||
|
|
assert!(z_near > 0.0 && z_far > 0.0);
|
||
|
|
|
||
|
|
//
|
||
|
|
// reversed z 0..1 projection based on https://thxforthefish.com/posts/reverse_z/
|
||
|
|
//
|
||
|
|
let a = (right + left) / (right - left);
|
||
|
|
let b: f32 = (top + bottom) / (top - bottom);
|
||
|
|
|
||
|
|
let c = z_near / (z_far - z_near);
|
||
|
|
let d = z_far * z_near / (z_far - z_near);
|
||
|
|
|
||
|
|
|
||
|
|
Mat4::from_cols(
|
||
|
|
Vec4::new(2.0 * z_near / (right-left),0.0,0.0,0.0),
|
||
|
|
Vec4::new(0.0, 2.0 * z_near / (top-bottom), 0.0,0.0),
|
||
|
|
Vec4::new(a, b, c, -1.0),
|
||
|
|
Vec4::new(0.0, 0.0, d, 0.0))
|
||
|
|
}
|
||
|
|
|
||
|
|
|
||
|
|
pub fn make_projection_rh_custom(fov_y: f32, aspect_ratio: f32, z_near: f32, z_far: f32) -> Mat4
|
||
|
|
{
|
||
|
|
let tan_fovy = (fov_y * 0.5).tan(); // use half angle beta
|
||
|
|
let right = tan_fovy * aspect_ratio * z_near;
|
||
|
|
let left = -right;
|
||
|
|
let top = tan_fovy * z_near;
|
||
|
|
let bottom = -top;
|
||
|
|
|
||
|
|
//make_projection_rh_from_frustum(left, right, bottom, top, z_near, z_far)
|
||
|
|
|
||
|
|
make_projection_rh_from_frustum_reversed(left, right, bottom, top, z_near, z_far)
|
||
|
|
}
|
||
|
|
|
||
|
|
|
||
|
|
#[cfg(test)]
|
||
|
|
mod tests {
|
||
|
|
use bevy::prelude::Mat4;
|
||
|
|
|
||
|
|
use super::make_projection_rh_from_frustum;
|
||
|
|
|
||
|
|
|
||
|
|
#[test]
|
||
|
|
fn compare_projections() {
|
||
|
|
|
||
|
|
// build an on-axis frustum
|
||
|
|
let fovy = 33.0_f32;
|
||
|
|
let aspect_ratio = 1.6666_f32;
|
||
|
|
let z_near = 1.0_f32;
|
||
|
|
let z_far = 1000.0_f32;
|
||
|
|
|
||
|
|
let tan_fovy = (fovy * 0.5).to_radians().tan(); // use half angle beta
|
||
|
|
let right = tan_fovy * aspect_ratio * z_near;
|
||
|
|
let left = -right;
|
||
|
|
let top = tan_fovy * z_near;
|
||
|
|
let bottom = -top;
|
||
|
|
|
||
|
|
let mat_frust = make_projection_rh_from_frustum(left, right, bottom, top, z_near, z_far);
|
||
|
|
|
||
|
|
println!("mat 1 {:?}",mat_frust);
|
||
|
|
|
||
|
|
let mat_pers = Mat4::perspective_rh_gl(fovy.to_radians(),aspect_ratio,z_near,z_far);
|
||
|
|
|
||
|
|
println!("mat 2 {:?}",mat_pers);
|
||
|
|
|
||
|
|
assert!(mat_frust.abs_diff_eq(mat_pers, f32::EPSILON));
|
||
|
|
|
||
|
|
}
|
||
|
|
|
||
|
|
}
|