61 lines
1.5 KiB
Rust
61 lines
1.5 KiB
Rust
use std::f64::consts::PI;
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use crate::math::Vec3;
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use super::{RandomDistribution, UnitDisc};
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#[derive(Default)]
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pub struct CosineWeightedHemisphere {
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unit_disc: UnitDisc,
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}
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impl CosineWeightedHemisphere {
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pub fn new() -> CosineWeightedHemisphere {
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let unit_disc = UnitDisc::new();
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CosineWeightedHemisphere { unit_disc }
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}
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}
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impl RandomDistribution<Vec3<f64>> for CosineWeightedHemisphere {
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fn value(&self) -> Vec3<f64> {
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let point_on_disc = self.unit_disc.value();
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let z = 0.0f64
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.max(
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1.0 - point_on_disc.x() * point_on_disc.x() - point_on_disc.y() * point_on_disc.y(),
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)
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.sqrt();
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Vec3::new(point_on_disc.x(), point_on_disc.y(), z)
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}
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fn pdf(&self, v: Vec3<f64>) -> f64 {
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(v.x() * v.x() + v.y() * v.y()).sqrt() / PI
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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#[ignore]
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fn print_values() {
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let target = CosineWeightedHemisphere::new();
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for _ in 0..1000 {
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let value = target.value();
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println!("{}, {}, {}", value.x(), value.y(), value.z());
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}
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}
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#[test]
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#[ignore]
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fn integral_is_near_area() {
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let target = CosineWeightedHemisphere::new();
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let integral = (0..100000)
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.map(|_| target.value())
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.map(|value| 1.0 / target.pdf(value))
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.sum::<f64>()
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/ 100000.0;
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println!("Area: {}\nIntegral: {}", 2.0 * PI, integral);
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}
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}
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