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use bevy_math::{Mat4, Vec3, Vec4};
/// A distance calculator for the draw order of [`PhaseItem`](crate::render_phase::PhaseItem)s.
pub struct ViewRangefinder3d {
view_from_world_row_2: Vec4,
}
impl ViewRangefinder3d {
/// Creates a 3D rangefinder for a view matrix.
pub fn from_world_from_view(world_from_view: &Mat4) -> ViewRangefinder3d {
let view_from_world = world_from_view.inverse();
ViewRangefinder3d {
view_from_world_row_2: view_from_world.row(2),
}
}
/// Calculates the distance, or view-space `Z` value, for the given `translation`.
#[inline]
pub fn distance_translation(&self, translation: &Vec3) -> f32 {
// NOTE: row 2 of the inverse view matrix dotted with the translation from the model matrix
// gives the z component of translation of the mesh in view-space
self.view_from_world_row_2.dot(translation.extend(1.0))
}
/// Calculates the distance, or view-space `Z` value, for the given `transform`.
#[inline]
pub fn distance(&self, transform: &Mat4) -> f32 {
// NOTE: row 2 of the inverse view matrix dotted with column 3 of the model matrix
// gives the z component of translation of the mesh in view-space
self.view_from_world_row_2.dot(transform.col(3))
}
}
#[cfg(test)]
mod tests {
use super::ViewRangefinder3d;
use bevy_math::{Mat4, Vec3};
#[test]
fn distance() {
let view_matrix = Mat4::from_translation(Vec3::new(0.0, 0.0, -1.0));
let rangefinder = ViewRangefinder3d::from_world_from_view(&view_matrix);
assert_eq!(rangefinder.distance(&Mat4::IDENTITY), 1.0);
assert_eq!(
rangefinder.distance(&Mat4::from_translation(Vec3::new(0.0, 0.0, 1.0))),
2.0
);
}
}