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// Copyright 2013-2014 The CGMath Developers. For a full listing of the authors,
// refer to the Cargo.toml file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use std::marker::PhantomData;
use cgmath::{BaseFloat, BaseNum, InnerSpace};
use cgmath::{EuclideanSpace, Point2, Point3};
use cgmath::{VectorSpace, Vector2, Vector3};

use intersect::{Continuous, Discrete};


/// A generic ray starting at `origin` and extending infinitely in
/// `direction`.
#[derive(Copy, Clone, PartialEq)]
#[cfg_attr(feature = "eders", derive(Serialize, Deserialize))]
pub struct Ray<S, P, V> {
    pub origin: P,
    pub direction: V,
    phantom_s: PhantomData<S>,
}

impl<S, V, P> Ray<S, P, V>
where
    S: BaseNum,
    V: VectorSpace<Scalar = S>,
    P: EuclideanSpace<Scalar = S, Diff = V>,
{
    pub fn new(origin: P, direction: V) -> Ray<S, P, V> {
        Ray {
            origin: origin,
            direction: direction,
            phantom_s: PhantomData,
        }
    }
}

pub type Ray2<S> = Ray<S, Point2<S>, Vector2<S>>;
pub type Ray3<S> = Ray<S, Point3<S>, Vector3<S>>;

impl<S, P> Continuous<Ray<S, P, P::Diff>, P> for P
where
    S: BaseFloat,
    P: EuclideanSpace<Scalar = S>,
    P::Diff: InnerSpace<Scalar = S>,
{
    fn intersection(&self, ray: &Ray<S, P, P::Diff>) -> Option<P> {
        if self.intersects(ray) {
            Some(self.clone())
        } else {
            None
        }
    }
}

impl<S, P> Discrete<Ray<S, P, P::Diff>> for P
where
    S: BaseFloat,
    P: EuclideanSpace<Scalar = S>,
    P::Diff: InnerSpace<Scalar = S>,
{
    fn intersects(&self, ray: &Ray<S, P, P::Diff>) -> bool {
        let p = self.clone();
        let l = p - ray.origin;
        let tca = l.dot(ray.direction);
        tca > S::zero() &&
            (tca * tca).relative_eq(
                &l.magnitude2(),
                S::default_epsilon(),
                S::default_max_relative(),
            )
    }
}