SphericalSampling.dib

#!meta

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#!csharp

#r "nuget: TinyEmbree"
#r "nuget: SimpleImageIO"
#r "../SeeSharp/bin/Debug/net7.0/SeeSharp.dll"

using SeeSharp;
using SeeSharp.Sampling;
using SeeSharp.Integrators;
using SeeSharp.Experiments;
using SeeSharp.Geometry;
using TinyEmbree;
using SimpleImageIO;
using SimpleImageIO.FlipBook;
using System.Numerics;
using System;
using System.Threading.Tasks;

// Avoids slowing down the Jupyter Kernel with console spam
SeeSharp.Common.ProgressBar.Silent = true;

HTML(FlipBook.MakeHeader()).Display();

#!csharp

SceneRegistry.AddSource("../Data/Scenes");
var sceneConfig = SceneRegistry.LoadScene("CornellBox");
var reference = sceneConfig.GetReferenceImage(512, 512);
var scene = sceneConfig.MakeScene();
scene.FrameBuffer = new(512, 512, "");
scene.Prepare();

#!csharp

abstract class DirectIllum : Integrator {
    protected Scene scene;

    public DirectIllum(int spp) {
        SampleCount = spp;
    }

    public override void Render(Scene scene) {
        this.scene = scene;

        for (uint sampleIndex = 0; sampleIndex < SampleCount; ++sampleIndex) {
            scene.FrameBuffer.StartIteration();
            Parallel.For(0, scene.FrameBuffer.Height, row => {
                for (uint col = 0; col < scene.FrameBuffer.Width; ++col) {
                    uint pixelIndex = (uint)(row * scene.FrameBuffer.Width + col);
                    RNG rng = new(BaseSeed, pixelIndex, sampleIndex);
                    RenderPixel((uint)row, col, rng);
                }
            });
            scene.FrameBuffer.EndIteration();
        }
    }

    private void RenderPixel(uint row, uint col, RNG rng) {
        var offset = rng.NextFloat2D();
        var pixel = new Vector2(col, row) + offset;
        var primaryRay = scene.Camera.GenerateRay(pixel, rng).Ray;
        var primaryHit = scene.Raytracer.Trace(primaryRay);

        if (primaryHit) {
            var estimate = EstimateIncidentRadiance(primaryRay, primaryHit, rng);
            scene.FrameBuffer.Splat(col, row, estimate);
        }
    }

    protected abstract RgbColor EstimateIncidentRadiance(in Ray ray, in SurfacePoint hit, RNG rng);
}

#!csharp

class UniformArea : DirectIllum {
    public UniformArea(int spp) : base(spp) { }

    protected override RgbColor EstimateIncidentRadiance(in Ray ray, in SurfacePoint hit, RNG rng) {
        // Select a light source
        var light = scene.Emitters[rng.NextInt(0, scene.Emitters.Count)];
        float lightSelectProb = 1.0f / scene.Emitters.Count;

        // Sample a point on the light source
        var lightSample = light.SampleUniformArea(rng.NextFloat2D());
        Vector3 lightToSurface = Vector3.Normalize(hit.Position - lightSample.Point.Position);

        if (!scene.Raytracer.IsOccluded(hit, lightSample.Point)) {
            var emission = light.EmittedRadiance(lightSample.Point, lightToSurface);
            float jacobian = SampleWarp.SurfaceAreaToSolidAngle(hit, lightSample.Point);
            var bsdfCos = hit.Material.EvaluateWithCosine(hit, -ray.Direction, -lightToSurface, false);
            var pdf = lightSample.Pdf * lightSelectProb;
            return emission / pdf * jacobian * bsdfCos;
        }
        return RgbColor.Black;
    }
}

#!csharp

class SolidAngle : DirectIllum {
    public SolidAngle(int spp) : base(spp) { }

    protected override RgbColor EstimateIncidentRadiance(in Ray ray, in SurfacePoint hit, RNG rng) {
        // Select a light source
        var light = scene.Emitters[rng.NextInt(0, scene.Emitters.Count)];
        float lightSelectProb = 1.0f / scene.Emitters.Count;

        // Sample a point on the light source
        var lightSample = light.SampleSolidAngle(hit, rng.NextFloat2D());
        Vector3 lightToSurface = Vector3.Normalize(hit.Position - lightSample.Point.Position);

        if (!scene.Raytracer.IsOccluded(hit, lightSample.Point)) {
            var emission = light.EmittedRadiance(lightSample.Point, lightToSurface);
            float jacobian = SampleWarp.SurfaceAreaToSolidAngle(hit, lightSample.Point);
            var bsdfCos = hit.Material.EvaluateWithCosine(hit, -ray.Direction, -lightToSurface, false);
            var pdf = lightSample.Pdf * lightSelectProb;
            return emission / pdf * jacobian * bsdfCos;
        }
        return RgbColor.Black;
    }
}

#!csharp

scene.FrameBuffer = new(512, 512, "");
new UniformArea(1).Render(scene);
var uniform = scene.FrameBuffer.Image;

scene.FrameBuffer = new(512, 512, "");
new SolidAngle(1).Render(scene);
var solidAngle = scene.FrameBuffer.Image;

Metrics.RelMSE(uniform, reference).Display();
Metrics.RelMSE(solidAngle, reference).Display();

HTML(FlipBook.Make(("uniform", uniform), ("spherical", solidAngle)))