rustic-zen 0.3.0

// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.

/// Some considerations for adding curve support to this:
/// https://blog.demofox.org/2016/03/05/matrix-form-of-bezier-curves/
/// https://pomax.github.io/bezierinfo/
/// https://computergraphics.stackexchange.com/questions/374/how-to-raytrace-bezier-surfaces/378
/// https://en.wikipedia.org/wiki/B-spline
/// https://en.wikipedia.org/wiki/B%C3%A9zier_curve
///
/// Micha's zenphoton did not actually collide curves, curves were implemented only with their normals,
///  which seemed to work well, although I would be lying if I said I understood why. It seems to me
/// that more comtrollable results could be achieved with besier curves, but it seems the computational
/// cost of adding these could be very high, which might explain zenphoton's use of a hack.
use crate::geom::{Matrix, Point, Vector};
use crate::material::Material;
use crate::sampler::SamplerPoint;

use rand::prelude::*;

/// Segments represent boundries in space for light rays to interact with.
///
/// These are the primitive type that scenes are constructed from in rustic zen,
/// and can be in the form of straight lines or 2nd order Bezier curves.
///
/// To create dynamic and interesting scenes segments are not constructed from static
/// points, but instead `SamplerPoint`s, which are a wrapper around two of rustic zen's `Sampler`
/// objects. (one for x and one for y).
///
/// As `SamplerPoint`s do not have a constructor, construction is indirect via a tuple of `Sampler`s.
/// # Example:
/// ```
/// use rustic_zen::prelude::*;
///
/// let m = material::hqz_legacy_default();
///
/// // Construct SamplerPoints in place from a tuple of Samplers.
/// let l =Segment::line_from_points(
///     (Sampler::new_const(0.0),Sampler::new_const(0.0)),
///     (Sampler::new_const(10.0),Sampler::new_const(10.0)),
///     m.clone()
/// );
///
/// // Samplers also support being constructed in place though so this can be simplified to
/// let l2 = Segment::line_from_points((0.0,0.0), (10.0, 10.0), m);
///
/// // You'll likely get compaints about missing type "R" if you don't add
/// // your Segments to the scene. Adding them constrains R.
/// let _ = Scene::new(100, 100).with_object(l).with_object(l2);
/// ```
pub struct Segment<R: Rng> {
    inner: Object<R>,
}

/// Holds a definition of an object
///
/// Interally contains the associated logic.
#[derive(Clone)]
pub(crate) enum Object<R: Rng> {
    /// Straight line variant
    Line {
        /// Material used
        material: Material<R>,
        /// Starting Position
        p0: SamplerPoint<R>,
        /// End Position
        p1: SamplerPoint<R>,
    },
    /// Curve Variant, Implemented as a Quadratic Bezier Curve
    Curve {
        /// Material used
        material: Material<R>,
        /// Bezier Start Locationa
        p0: SamplerPoint<R>,
        /// Bezier Curve Point
        p1: SamplerPoint<R>,
        /// Bezier End Location
        p2: SamplerPoint<R>,
    },
}

impl<R> Segment<R>
where
    R: Rng,
{
    /// Constructs a line from the given points and material.
    pub fn line_from_points<A, B>(start: A, end: B, material: Material<R>) -> Self
    where
        A: Into<SamplerPoint<R>>,
        B: Into<SamplerPoint<R>>,
    {
        let start = start.into();
        let end = end.into();
        Self {
            inner: Object::Line {
                material,
                p0: start.into(),
                p1: end.into(),
            },
        }
    }

    /// Constructs a Bezier curve from the given points, and material.
    ///
    /// __Note__: `mid` is the control point of the Bezier curve, the resulting path is not
    /// guarenteed to pass though this point.  
    pub fn curve_from_points<A, B, C>(start: A, mid: B, end: C, material: Material<R>) -> Self
    where
        A: Into<SamplerPoint<R>>,
        B: Into<SamplerPoint<R>>,
        C: Into<SamplerPoint<R>>,
    {
        let p0 = start.into();
        let p1 = mid.into();
        let p2 = end.into();
        Self {
            inner: Object::Curve {
                material,
                p0,
                p1,
                p2,
            },
        }
    }
}

impl<R> Object<R>
where
    R: Rng,
{
    /**
     * Returns a reference to the material used in this object
     */
    #[inline(always)]
    pub(crate) fn process_material(
        &self,
        direction: &Vector,
        normal: &Vector,
        wavelength: f64,
        alpha: f64,
        rng: &mut R,
    ) -> Option<Vector> {
        let material = match self {
            Object::Curve { material, .. } => material,
            Object::Line { material, .. } => material,
        };

        (material)(direction, normal, wavelength, alpha, rng)
    }

    #[inline(always)]
    fn get_line_hit(
        s1: Point,
        s2: Point,
        origin: &Point,
        dir: &Vector,
    ) -> Option<(Point, Vector, f64)> {
        let sd = s2 - s1;
        let mat_a = Matrix {
            a1: sd.x,
            b1: -dir.x,
            a2: sd.y,
            b2: -dir.y,
        };

        let omega = origin.clone() - s1;

        let result = match mat_a.inverse() {
            Some(m) => m * omega,
            None => {
                return None; // Probably cos rays are parallel
            }
        };
        if (result.x >= 0.0) && (result.x <= 1.0) && (result.y > 0.0) {
        } else {
            return None;
        };

        let alpha = result.x;
        let distance = result.y;

        let hit = *origin + (*dir * distance);
        let norm = Vector { x: -sd.y, y: sd.x };

        return Some((hit, norm, alpha));
    }

    #[inline(always)]
    fn get_point_on_bezier(p0: Point, p1: Point, p2: Point, alpha: f64) -> Point {
        let beta = 1.0 - alpha;
        ((p0.v() * beta * beta) + (p1.v() * beta * alpha * 2.0) + (p2.v() * alpha * alpha)).p()
    }

    #[inline(always)]
    fn get_normal_on_bezier(p0: Point, p1: Point, p2: Point, alpha: f64) -> Vector {
        let w0 = (p1 - p0) * 2.0;
        let w1 = (p2 - p1) * 2.0;
        (w0 * (1.0 - alpha) + w1 * alpha).normal()
    }

    #[inline(always)]
    fn process_curve_hit(
        p0: Point,
        p1: Point,
        p2: Point,
        origin: &Point,
        dir: &Vector,
        alpha: f64,
    ) -> Option<(f64, Point)> {
        if 0.0 >= alpha || alpha >= 1.0 {
            return None;
        }
        let hit = Self::get_point_on_bezier(p0, p1, p2, alpha);
        // bail out early if hit is behind emmitter;
        let ray_alpha = (hit.x - origin.x) / dir.x;
        if ray_alpha < 0.0 {
            return None;
        } else {
            Some((ray_alpha, hit))
        }
    }

    #[inline(always)]
    fn get_curve_hit(
        p0: Point,
        p1: Point,
        p2: Point,
        origin: &Point,
        dir: &Vector,
    ) -> Option<(Point, Vector, f64)> {
        // align coordinate system such that thee roots of the curve are the solutions.
        let rotation_matrix = Matrix {
            a1: dir.x,
            a2: dir.y,
            b1: dir.y,
            b2: -dir.x,
        };

        let pa0 = rotation_matrix * (p0 - *origin).p();
        let pa1 = rotation_matrix * (p1 - *origin).p();
        let pa2 = rotation_matrix * (p2 - *origin).p();
        let a = pa0.y;
        let b = pa1.y;
        let c = pa2.y;
        let d = a - 2.0 * b + c;

        if d.abs() > 0.0001 {
            let m1 = -f64::sqrt(b * b - a * c);
            let m2 = b - a;
            let v1 = -(m1 + m2) / d;
            let v2 = -(-m1 + m2) / d;
            let r1 = Self::process_curve_hit(p0, p1, p2, origin, dir, v1);
            let r2 = Self::process_curve_hit(p0, p1, p2, origin, dir, v2);
            if r1.is_none() && r2.is_none() {
                return None;
            }
            let (d1, hit1) = r1.unwrap_or((f64::MAX, (0.0, 0.0).into()));
            let (d2, hit2) = r2.unwrap_or((f64::MAX, (0.0, 0.0).into()));
            if d1 < d2 {
                let norm = Self::get_normal_on_bezier(p0, p1, p2, v1);
                Some((hit1, norm, v1))
            } else {
                let norm = Self::get_normal_on_bezier(p0, p1, p2, v2);
                Some((hit2, norm, v2))
            }
        } else {
            if b != c {
                let t = (2.0 * b - c) / (2.0 * b - 2.0 * c);
                let (_, hit) = Self::process_curve_hit(p0, p1, p2, origin, dir, t)?;
                let norm = Self::get_normal_on_bezier(p0, p1, p2, t);
                Some((hit, norm, t))
            } else {
                None
            }
        }
    }

    /**
     * Tests if the inbound ray actually hit the object,
     * if so it returns the coords of the hit, followed by the normal
     * to the hit surface.
     *
     * If miss it returns None
     *
     * This test assumes you have done a box test to
     * check the bounds of the line first
     */
    #[inline(always)]
    pub(crate) fn get_hit(
        &self,
        origin: &Point,
        dir: &Vector,
        rng: &mut R,
    ) -> Option<(Point, Vector, f64)> {
        match self {
            Object::Curve { p0, p1, p2, .. } => {
                Self::get_curve_hit(p0.get(rng), p1.get(rng), p2.get(rng), origin, dir)
            }
            Object::Line { p0, p1, .. } => {
                Self::get_line_hit(p0.get(rng), p1.get(rng), origin, dir)
            }
        }
    }
}

impl<R> From<Segment<R>> for Object<R>
where
    R: Rng,
{
    fn from(value: Segment<R>) -> Self {
        value.inner
    }
}

#[cfg(test)]
mod tests {
    type RandGen = rand_pcg::Pcg64Mcg;

    use crate::material::hqz_legacy_default;

    use super::Object;
    use super::Segment;

    use crate::geom::{Point, Vector};
    use crate::material::hqz_legacy;

    use rand::prelude::*;

    #[test]
    fn segment_into() {
        let s = Segment::line_from_points((0.0, 0.0), (10.0, 10.0), hqz_legacy_default());
        let _: Object<RandGen> = s.into();
        // we can't actually check for equlaity on the object or any of it's fields, so if this compiles we assume all is good.
    }

    #[test]
    /// Ray hits object test
    /// Test result should be a hit at (5,5)
    fn hit_line_1() {
        let mut rng = RandGen::from_entropy();

        let m = hqz_legacy(0.3, 0.3, 0.3);

        let obj = Object::Line {
            p0: (0.0, 0.0).into(),
            p1: (10.0, 10.0).into(),
            material: m,
        };

        let origin = Point { x: 10.0, y: 0.0 };
        let dir = Vector { x: -1.0, y: 1.0 };

        let a = obj.get_hit(&origin, &dir, &mut rng);

        let (a, b, _) = a.expect("A was not meant to be `None`");

        //assert hit is at (5,5)
        assert_eq!(a.x, 5.0);
        assert_eq!(a.y, 5.0);

        //assert normal is (-10,10)
        assert_eq!(b.x, -10.0);
        assert_eq!(b.y, 10.0);
        //normal is not normalised
    }

    #[test]
    /// Ray hits object test
    /// Test result should be a hit at (5,5)
    fn hit_curve_1() {
        let mut rng = RandGen::from_entropy();

        let m = hqz_legacy(0.3, 0.3, 0.3);

        let obj = Object::Curve {
            p0: (0.0, 0.0).into(),
            p1: (5.0, 5.0).into(),
            p2: (10.0, 10.0).into(),
            material: m,
        };

        let origin = Point { x: 0.0, y: 5.0 };
        let dir = Vector { x: 1.0, y: 0.0 };

        let a = obj.get_hit(&origin, &dir, &mut rng);

        let (a, b, _) = a.expect("A was not meant to be `None`");

        //assert hit is at (5,5)
        assert_eq!(a.x, 5.0);
        assert_eq!(a.y, 5.0);

        // //assert normal is (-10,10)
        assert_eq!(b.x, -10.0);
        assert_eq!(b.y, 10.0);
        //normal is not normalised
    }

    #[test]
    /// Ray hits object test
    /// Test result should be a hit at (5,5)
    fn hit_curve_2() {
        let mut rng = RandGen::from_entropy();

        let m = hqz_legacy(0.3, 0.3, 0.3);

        let obj = Segment::curve_from_points((0.0, 0.0), (5.0, 5.0), (10.0, 10.0), m).inner;

        let origin = Point { x: 0.0, y: 10.0 };
        let dir = Vector { x: 1.0, y: -1.0 };

        let a = obj.get_hit(&origin, &dir, &mut rng);

        let (a, b, _) = a.expect("A was not meant to be `None`");

        //assert hit is at (5,5)
        assert_eq!(a.x, 5.0);
        assert_eq!(a.y, 5.0);

        //assert normal is (-10,10)
        assert_eq!(b.x, -10.0);
        assert_eq!(b.y, 10.0);
        //normal is not normalised
    }

    #[test]
    /// Ray hits object test
    /// Test result should be a hit at (5,5)
    fn hit_curve_horz() {
        let mut rng = RandGen::from_entropy();

        let m = hqz_legacy(0.3, 0.3, 0.3);

        let obj = Segment::curve_from_points((0.0, 5.0), (5.0, 5.0), (10.0, 5.0), m).inner;

        let origin = Point { x: 5.0, y: 0.0 };
        let dir = Vector { x: 0.0, y: 1.0 };

        let a = obj.get_hit(&origin, &dir, &mut rng);

        let (a, b, _) = a.expect("A was not meant to be `None`");

        //assert hit is at (5,5)
        assert_eq!(a.x.round(), 5.0);
        assert_eq!(a.y.round(), 5.0);

        //assert normal is (-10,10)
        assert_eq!(b.x.round(), 0.0);
        assert_eq!(b.y.round(), 10.0);
        //normal is not normalised
    }

    #[test]
    /// Ray hits object test
    /// Test result should be a hit at (5,5)
    fn hit_curve_vert() {
        let mut rng = RandGen::from_entropy();

        let m = hqz_legacy(0.3, 0.3, 0.3);

        let obj = Segment::curve_from_points((5.0, 0.0), (5.0, 5.0), (5.0, 10.0), m).inner;

        let origin = Point { x: 0.0, y: 5.0 };
        let dir = Vector { x: 1.0, y: 0.0 };

        let a = obj.get_hit(&origin, &dir, &mut rng);

        let (a, b, _) = a.expect("A was not meant to be `None`");

        //assert hit is at (5,5)
        assert_eq!(a.x, 5.0);
        assert_eq!(a.y, 5.0);

        //assert normal is (-10,10)
        assert_eq!(b.x.round(), -10.0);
        assert_eq!(b.y.round(), 0.0);
        //normal is not normalised
    }

    #[test]
    /// Vector misses the object test
    /// Test result should be None as Ray crosses dy/dx
    /// Past the end of the object.
    fn miss_line_1() {
        let mut rng = RandGen::from_entropy();

        let m = hqz_legacy(0.3, 0.3, 0.3);

        let obj = Segment::line_from_points((0.0, 0.0), (10.0, 10.0), m).inner;

        let origin = Point { x: 30.0, y: 0.0 };
        let dir = Vector { x: -1.0, y: 1.0 };

        let a = obj.get_hit(&origin, &dir, &mut rng);

        assert!(a.is_none());
    }

    #[test]
    /// Vector Going the wrong way test
    /// Test result should be None, as Ray is going 180°
    /// in the wrong direction to hit the object.
    fn miss_line_2() {
        let mut rng = RandGen::from_entropy();

        let m = hqz_legacy(0.3, 0.3, 0.3);

        let obj = Segment::line_from_points((0.0, 0.0), (10.0, 10.0), m).inner;

        let origin = Point { x: 10.0, y: 0.0 };
        let dir = Vector { x: 1.0, y: 1.0 };

        let a = obj.get_hit(&origin, &dir, &mut rng);

        assert!(a.is_none());
    }

    #[test]
    /// Vector misses the object test
    /// Test result should be None as Ray crosses dy/dx
    /// Past the end of the object.
    fn miss_curve_1() {
        let mut rng = RandGen::from_entropy();

        let m = hqz_legacy(0.3, 0.3, 0.3);

        let obj = Segment::curve_from_points((0.0, 0.0), (5.0, 5.0), (10.0, 10.0), m).inner;

        let origin = Point { x: 30.0, y: 0.0 };
        let dir = Vector { x: -1.0, y: 1.0 };

        let a = obj.get_hit(&origin, &dir, &mut rng);

        assert!(a.is_none());
    }

    #[test]
    /// Vector Going the wrong way test
    /// Test result should be None, as Ray is going 180°
    /// in the wrong direction to hit the object.
    fn miss_curve_2() {
        let mut rng = RandGen::from_entropy();

        let m = hqz_legacy(0.3, 0.3, 0.3);

        let obj = Segment::curve_from_points((0.0, 0.0), (5.0, 5.0), (10.0, 10.0), m).inner;

        let origin = Point { x: 10.0, y: 0.0 };
        let dir = Vector { x: 1.0, y: 1.0 };

        let a = obj.get_hit(&origin, &dir, &mut rng);

        assert!(a.is_none());
    }
}