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```//! Traits and structure needed to cast rays.

use crate::math::{Isometry, Point, Vector};
use crate::shape::FeatureId;
#[cfg(feature = "dim3")]
use na::Point2;
use na::RealField;

/// A Ray.
#[derive(Debug, Clone, Copy)]
pub struct Ray<N: RealField> {
/// Starting point of the ray.
pub origin: Point<N>,
/// Direction of the ray.
pub dir: Vector<N>,
}

impl<N: RealField> Ray<N> {
/// Creates a new ray starting from `origin` and with the direction `dir`. `dir` must be
/// normalized.
pub fn new(origin: Point<N>, dir: Vector<N>) -> Ray<N> {
Ray {
origin: origin,
dir: dir,
}
}

/// Transforms this ray by the given isometry.
#[inline]
pub fn transform_by(&self, m: &Isometry<N>) -> Self {
Self::new(m * self.origin, m * self.dir)
}

/// Transforms this ray by the inverse of the given isometry.
#[inline]
pub fn inverse_transform_by(&self, m: &Isometry<N>) -> Self {
Self::new(
m.inverse_transform_point(&self.origin),
m.inverse_transform_vector(&self.dir),
)
}

/// Translates this ray by the given vector. Its direction is left unchanged.
#[inline]
pub fn translate_by(&self, v: Vector<N>) -> Self {
Self::new(self.origin + v, self.dir)
}

/// Computes the point at the given parameter on this line.
///
/// This computes `self.origin + self.dir * t`.
#[inline]
pub fn point_at(&self, t: N) -> Point<N> {
self.origin + self.dir * t
}
}

/// Structure containing the result of a successful ray cast.
#[derive(Copy, Clone, Debug)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub struct RayIntersection<N: RealField> {
/// The time of impact of the ray with the object.  The exact contact point can be computed
/// with: `ray.point_at(toi)` or equivalently `origin + dir * toi` where `origin` is the origin of the ray;
/// `dir` is its direction and `toi` is the value of this field.
pub toi: N,

/// The normal at the intersection point.
///
/// If the `toi` is exactly zero, the normal might not be reliable.
// XXX: use a Unit<Vetor<N>> instead.
pub normal: Vector<N>,

/// Feature at the intersection point.
pub feature: FeatureId,

/// The textures coordinates at the intersection point.  This is an `Option` because some shape
/// do not support texture coordinates.
#[cfg(feature = "dim3")]
pub uvs: Option<Point2<N>>,
}

impl<N: RealField> RayIntersection<N> {
#[inline]
/// Creates a new `RayIntersection`.
#[cfg(feature = "dim3")]
pub fn new_with_uvs(
toi: N,
normal: Vector<N>,
feature: FeatureId,
uvs: Option<Point2<N>>,
) -> RayIntersection<N> {
RayIntersection {
toi,
normal,
feature,
uvs,
}
}

#[inline]
/// Creates a new `RayIntersection`.
#[cfg(feature = "dim3")]
pub fn new(toi: N, normal: Vector<N>, feature: FeatureId) -> RayIntersection<N> {
RayIntersection {
toi,
normal,
feature,
uvs: None,
}
}

#[inline]
/// Creates a new `RayIntersection`.
#[cfg(feature = "dim2")]
pub fn new(toi: N, normal: Vector<N>, feature: FeatureId) -> RayIntersection<N> {
RayIntersection {
toi,
normal,
feature,
}
}
}

/// Traits of objects which can be transformed and tested for intersection with a ray.
pub trait RayCast<N: RealField> {
/// Computes the time of impact between this transform shape and a ray.
fn toi_with_ray(&self, m: &Isometry<N>, ray: &Ray<N>, max_toi: N, solid: bool) -> Option<N> {
self.toi_and_normal_with_ray(m, ray, max_toi, solid)
.map(|inter| inter.toi)
}

/// Computes the time of impact, and normal between this transformed shape and a ray.
fn toi_and_normal_with_ray(
&self,
m: &Isometry<N>,
ray: &Ray<N>,
max_toi: N,
solid: bool,
) -> Option<RayIntersection<N>>;

/// Computes time of impact, normal, and texture coordinates (uv) between this transformed
/// shape and a ray.
#[cfg(feature = "dim3")]
#[inline]
fn toi_and_normal_and_uv_with_ray(
&self,
m: &Isometry<N>,
ray: &Ray<N>,
max_toi: N,
solid: bool,
) -> Option<RayIntersection<N>> {
self.toi_and_normal_with_ray(m, ray, max_toi, solid)
}

/// Tests whether a ray intersects this transformed shape.
#[inline]
fn intersects_ray(&self, m: &Isometry<N>, ray: &Ray<N>, max_toi: N) -> bool {
self.toi_with_ray(m, ray, max_toi, true).is_some()
}
}
```