pbrt/shared/src/lights/projection.rs

use crate::{
    spectra::{RGB, RGBColorSpace},
    utils::{Transform, sampling::PiecewiseConstant2D},
};

#[repr(C)]
#[derive(Clone, Copy, Debug)]
pub struct ProjectionLight {
    pub base: LightBase,
    pub scale: Float,
    pub hither: Float,
    pub screen_bounds: Bounds2f,
    pub screen_from_light: Transform,
    pub light_from_screen: Transform,
    pub image_id: u32,
    pub a: Float,
    pub distrib: PiecewiseConstant2D,
    pub image_color_space: *const RGBColorSpace,
}

impl ProjectionLight {
    pub fn new(
        render_from_light: Transform,
        medium_interface: MediumInterface,
        image_id: u32,
        image_color_space: RGBColorSpace,
        scale: Float,
        fov: Float,
    ) -> Self {
        let base = LightBase::new(
            LightType::DeltaPosition,
            &render_from_light,
            &medium_interface,
        );
        let image = Image::new();
        let aspect = image.resolution().x() as Float / image.resolution().y() as Float;
        let screen_bounds = if aspect > 1. {
            Bounds2f::from_points(Point2f::new(-aspect, -1.), Point2f::new(aspect, 1.))
        } else {
            Bounds2f::from_points(
                Point2f::new(-1., 1. / aspect),
                Point2f::new(1., 1. / aspect),
            )
        };

        let hither = 1e-3;
        let screen_from_light = TransformGeneric::perspective(fov, hither, 1e30).unwrap();
        let light_from_screen = screen_from_light.inverse();
        let opposite = (radians(fov) / 2.).tan();
        let aspect_ratio = if aspect > 1. { aspect } else { 1. / aspect };
        let a = 4. * square(opposite) * aspect_ratio;
        let dwda = |p: Point2f| {
            let w =
                Vector3f::from(light_from_screen.apply_to_point(Point3f::new(p.x(), p.y(), 0.)));
            cos_theta(w.normalize()).powi(3)
        };

        let d = image.get_sampling_distribution(dwda, screen_bounds);
        let distrib = PiecewiseConstant2D::new_with_bounds(&d, screen_bounds);

        Self {
            base,
            image_id,
            image_color_space,
            screen_bounds,
            screen_from_light,
            light_from_screen,
            scale,
            hither,
            a,
            distrib,
        }
    }

    pub fn i(&self, w: Vector3f, lambda: SampledWavelengths) -> SampledSpectrum {
        if w.z() < self.hither {
            return SampledSpectrum::new(0.);
        }
        let ps = self.screen_from_light.apply_to_point(w.into());
        if !self.screen_bounds.contains(Point2f::new(ps.x(), ps.y())) {
            return SampledSpectrum::new(0.);
        }
        let uv = Point2f::from(self.screen_bounds.offset(&Point2f::new(ps.x(), ps.y())));
        let mut rgb = RGB::default();
        for c in 0..3 {
            rgb[c] = self.image.lookup_nearest_channel(uv, c);
        }
        let s = RGBIlluminantSpectrum::new(self.image_color_space.as_ref(), RGB::clamp_zero(rgb));
        self.scale * s.sample(&lambda)
    }
}

impl LightTrait for ProjectionLight {
    fn base(&self) -> &LightBase {
        &self.base
    }

    fn sample_li(
        &self,
        _ctx: &LightSampleContext,
        _u: Point2f,
        _lambda: &SampledWavelengths,
        _allow_incomplete_pdf: bool,
    ) -> Option<LightLiSample> {
        todo!()
    }

    fn pdf_li(
        &self,
        _ctx: &LightSampleContext,
        _wi: Vector3f,
        _allow_incomplete_pdf: bool,
    ) -> Float {
        todo!()
    }

    fn l(
        &self,
        _p: Point3f,
        _n: Normal3f,
        _uv: Point2f,
        _w: Vector3f,
        _lambda: &SampledWavelengths,
    ) -> SampledSpectrum {
        todo!()
    }

    fn le(&self, _ray: &Ray, _lambda: &SampledWavelengths) -> SampledSpectrum {
        todo!()
    }

    fn phi(&self, lambda: SampledWavelengths) -> SampledSpectrum {
        let mut sum = SampledSpectrum::new(0.);
        for y in 0..self.image.resolution.y() {
            for x in 0..self.image.resolution.x() {
                let ps = self.screen_bounds.lerp(Point2f::new(
                    (x as Float + 0.5) / self.image.resolution.x() as Float,
                    (y as Float + 0.5) / self.image.resolution.y() as Float,
                ));
                let w_raw = Vector3f::from(self.light_from_screen.apply_to_point(Point3f::new(
                    ps.x(),
                    ps.y(),
                    0.,
                )));
                let w = w_raw.normalize();
                let dwda = cos_theta(w).powi(3);
                let mut rgb = RGB::default();
                for c in 0..3 {
                    rgb[c] = self.image.get_channel(Point2i::new(x, y), c);
                }

                let s = RGBIlluminantSpectrum::new(
                    self.image_color_space.as_ref(),
                    RGB::clamp_zero(rgb),
                );
                sum += s.sample(&lambda) * dwda;
            }
        }
        self.scale * self.a * sum / (self.image.resolution.x() * self.image.resolution.y()) as Float
    }

    fn preprocess(&mut self, _scene_bounds: &Bounds3f) {
        todo!()
    }

    fn bounds(&self) -> Option<LightBounds> {
        todo!()
    }
}