cgmath/src/cgmath/sphere.rs

// Copyright 2013 The CGMath Developers. For a full listing of the authors,
// refer to the AUTHORS 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.

//! Bounding sphere

use intersect::Intersect;
use point::{Point, Point3};
use ray::Ray3;
use vector::Vector;
use partial_ord::PartOrdFloat;

use std::num::NumCast;
use std::num;

fn cast<T: NumCast, U: NumCast>(n: T) -> U {
            num::cast(n).unwrap()
}

#[deriving(Clone, Eq)]
pub struct Sphere<S> {
    center: Point3<S>,
    radius: S,
}

impl<S: PartOrdFloat<S>> Intersect<Option<Point3<S>>> for (Sphere<S>, Ray3<S>) {
    fn intersection(&self) -> Option<Point3<S>> {
        match *self {
            (ref s, ref r) => {
                let l = s.center.sub_p(&r.origin);
                let tca = l.dot(&r.direction);
                if tca < cast(0.0) { return None; }
                let d2 = l.dot(&l) - tca*tca;
                if d2 > s.radius*s.radius { return None; }
                let thc = num::sqrt(s.radius*s.radius - d2);
                Some(r.origin.add_v(&r.direction.mul_s(tca - thc)))
            }
        }
    }
}