pbrt/src/lights/goniometric.rs

use std::path::Path;

use crate::core::image::{Image, ImageIO};
use crate::core::light::{CreateLight, lookup_spectrum};
use crate::core::spectrum::spectrum_to_photometric;
use crate::core::texture::FloatTexture;
use crate::utils::sampling::PiecewiseConstant2D;
use crate::utils::{Arena, FileLoc, ParameterDictionary, resolve_filename};
use anyhow::{Result, anyhow};
use shared::core::geometry::Point2i;
use shared::core::light::{Light, LightBase, LightType};
use shared::core::medium::{Medium, MediumInterface};
use shared::core::shape::Shape;
use shared::core::spectrum::Spectrum;
use shared::core::texture::SpectrumType;
use shared::lights::GoniometricLight;
use shared::spectra::RGBColorSpace;
use shared::utils::{Ptr, Transform};
use shared::{Float, PI};

pub trait CreateGoniometricLight {
    fn new(
        render_from_light: Transform,
        medium_interface: MediumInterface,
        le: Spectrum,
        scale: Float,
        image: Ptr<Image>,
    ) -> Self;
}

impl CreateGoniometricLight for GoniometricLight {
    fn new(
        render_from_light: Transform,
        medium_interface: MediumInterface,
        le: Spectrum,
        scale: Float,
        image: Ptr<Image>,
    ) -> Self {
        let base = LightBase::new(
            LightType::DeltaPosition,
            render_from_light,
            medium_interface,
        );

        let iemit = lookup_spectrum(&le);
        let distrib = PiecewiseConstant2D::from_image(&image);
        Self {
            base,
            iemit: Ptr::from(&iemit.device()),
            scale,
            image: Ptr::from(image.device()),
            distrib: Ptr::from(&distrib.device),
        }
    }
}

impl CreateLight for GoniometricLight {
    fn create(
        render_from_light: Transform,
        medium: Medium,
        params: &ParameterDictionary,
        loc: &FileLoc,
        _shape: &Shape,
        _alpha_text: &FloatTexture,
        colorspace: Option<&RGBColorSpace>,
        _arena: &Arena,
    ) -> Result<Light> {
        let i = params
            .get_one_spectrum(
                "I",
                Some(Spectrum::Dense(colorspace.unwrap().illuminant)),
                SpectrumType::Illuminant,
            )
            .expect("Could not retrieve spectrum");
        let mut scale = params.get_one_float("scale", 1.)?;
        let filename = resolve_filename(&params.get_one_string("filename", "")?);
        let image: Ptr<Image> = if filename.is_empty() {
            Ptr::null()
        } else {
            let im = Image::read(Path::new(&filename), None)
                .map_err(|e| anyhow!("could not load image '{}': {}", filename, e))?;

            let loaded = im.image;
            let res = loaded.resolution();

            if loaded.has_any_infinite_pixels() {
                return Err(anyhow!(
                    "image '{}' has infinite pixels, not suitable for light",
                    filename
                ));
            }

            if res.x() != res.y() {
                return Err(anyhow!(
                    "image resolution ({}, {}) is non-square; unlikely to be an equal-area map",
                    res.x(),
                    res.y()
                ));
            }

            Ptr::from(&convert_to_luminance_image(&loaded, &filename, loc)?)
        };

        scale /= spectrum_to_photometric(i);
        let phi_v = params.get_one_float("power", -1.0)?;

        if phi_v > 0.0 {
            let k_e = compute_emissive_power(&image);
            scale *= phi_v / k_e;
        }

        let swap_yz: [Float; 16] = [
            1., 0., 0., 0., 0., 0., 1., 0., 0., 1., 0., 0., 0., 0., 0., 1.,
        ];
        let t = Transform::from_flat(&swap_yz)
            .expect("Could not create transform for GoniometricLight");
        let final_render_from_light = render_from_light * t;

        let specific =
            GoniometricLight::new(final_render_from_light, medium.into(), i, scale, image);

        Ok(Light::Goniometric(specific))
    }
}

fn convert_to_luminance_image(image: &Image, filename: &str, loc: &FileLoc) -> Result<Image> {
    let res = image.resolution();
    let rgb_desc = image.get_channel_desc(&["R", "G", "B"]);
    let y_desc = image.get_channel_desc(&["Y"]);

    match (rgb_desc, y_desc) {
        (Ok(_), Ok(_)) => Err(anyhow!(
            "{}: Image '{}' has both RGB and Y channels; ambiguous",
            loc,
            filename
        )),

        (Ok(_), Err(_)) => {
            // Convert RGB to Y (luminance)
            let mut y_pixels = Vec::with_capacity((res.x() * res.y()) as usize);

            for y in 0..res.y() {
                for x in 0..res.x() {
                    let r = image.get_channel(Point2i::new(x, y), 0);
                    let g = image.get_channel(Point2i::new(x, y), 1);
                    let b = image.get_channel(Point2i::new(x, y), 2);
                    y_pixels.push((r + g + b) / 3.0);
                }
            }

            Ok(Image::from_f32(y_pixels, res, &["Y"].to_vec()))
        }

        (Err(_), Ok(_)) => {
            // Already has Y channel
            Ok(image.clone())
        }

        (Err(_), Err(_)) => Err(anyhow!(
            "{}: Image '{}' has neither RGB nor Y channels",
            loc,
            filename
        )),
    }
}

fn compute_emissive_power(image: &Image) -> Float {
    let res = image.resolution();
    let mut sum_y = 0.0;

    for y in 0..res.y() {
        for x in 0..res.x() {
            sum_y += image.get_channel(Point2i::new(x, y), 0);
        }
    }

    4.0 * PI * sum_y / (res.x() * res.y()) as Float
}