Raytracer 光反射错误

Question

我正在尝试将 smallpt: Global Illumination in 99 lines of C++ 移植到 C#，但当光线从漫反射表面反射时，我遇到了这个奇怪的错误。有谁知道问题出在哪里？

This what I'm getting with 40 samples

This is what it's supposed to look like

这是我的漫反射表面代码：

if(sphere.Reflection == Sphere.ReflectionType.DIFFUSE)
        {
            double angleRand = random.NextDouble(seed) *2f*Math.PI;
            double distanceRand = random.NextDouble(seed);
            double distanceRandSqtr = Math.Sqrt(distanceRand);

            Vector3 w = surfaceNormal;
            Vector3 u = Vector3.Normalize(Vector3.Cross(Math.Abs(w.X) > .1 ? new Vector3(0f, 1f, 0f) : new Vector3(1f, 0f, 0f), w));
            Vector3 v = Vector3.Cross(w, u);

            Vector3 ref1 = Vector3.Multiply(u, (float)Math.Cos(angleRand));
            ref1 = Vector3.Multiply(ref1, (float)distanceRandSqtr);
            Vector3 ref2 = Vector3.Multiply(v, (float)Math.Sin(angleRand));
            ref2 = Vector3.Multiply(ref2, (float)distanceRandSqtr);
            Vector3 ref3 = Vector3.Multiply(w, (float)Math.Sqrt(1 - distanceRand));
            Vector3 ref4 = Vector3.Add(ref1, ref2);
            ref4 = Vector3.Add(ref4, ref3);

            Vector3 reflectionRayRand = Vector3.Normalize(ref4);

            Vector3 nextRadiance = ComputeRadiance(new Ray(intersectionPoint, reflectionRayRand), depth, seed);

            Vector3 result = Vector3.Multiply(color, nextRadiance);
            result = Vector3.Add(sphere.Emission, result);

            if (float.IsNaN(result.X) || float.IsNaN(result.Y) || float.IsNaN(result.Z))
            {
                throw new Exception();
            } 

            return result;
        }

这是原文：

if (obj.refl == DIFF){                  // Ideal DIFFUSE reflection
double r1=2*M_PI*erand48(Xi), r2=erand48(Xi), r2s=sqrt(r2);
Vec w=nl, u=((fabs(w.x)>.1?Vec(0,1):Vec(1))%w).norm(), v=w%u;
Vec d = (u*cos(r1)*r2s + v*sin(r1)*r2s + w*sqrt(1-r2)).norm();
return obj.e + f.mult(radiance(Ray(x,d),depth,Xi));}

Answer 1

你得到的效果让我想起了一点阴影粉刺。通常这是一个更圆形的图案，这就是我不确定的原因。阴影痤疮的发生是由于浮动不准确。当你散射或反射时，你会从一个表面上的某个原点沿一个方向产生一条新射线。原点有时会根据浮点误差移动 under/above 表面。这就是为什么您经常在法线方向上用少量 EPSILON 偏移光线。所以你的新原点变成：intersection + intersection.normal * EPSILON。您应该测试 epsilon 的不同值，但通常在 0.01 到 0.02 左右或附近。在您的代码中，您仍在使用交点，我认为它没有偏移量。我不确定这是否有效，因为你的结果看起来与我习惯的阴影痤疮有点不同，但值得一试，对吗？

Answer 2

我放弃了 Vector3 并使用了自定义的 class，它适用于双精度而不是浮点数。这解决了问题。感谢@AmberElferink 的帮助！

class Vec
{
    public double X { get; set; }
    public double Y { get; set; }

    public double Z { get; set; }

    public Vec(double x=0, double y=0, double z=0)
    {
        X = x;
        Y = y;
        Z = z;
    }

    public static Vec Normalize(Vec vec) { return vec.GetNormal(); }

    public static Vec Cross(Vec right, Vec left) { return right.CrossWith(left); }

    public static double Dot(Vec right, Vec left) { return right.DotWith(left); }

    public static Vec Multiply(Vec right, Vec left) { return right * left; }

    public static Vec Multiply(Vec right, double left) { return right * left; }

    public static Vec Add(Vec right, Vec left) { return right + left; }

    public static Vec Subtract(Vec right, Vec left) { return right - left; }

    public static Vec operator+(Vec right, Vec left) { return new Vec(right.X + left.X, right.Y + left.Y, right.Z + left.Z); }
    public static Vec operator-(Vec right, Vec left) { return new Vec(right.X - left.X, right.Y - left.Y, right.Z - left.Z); }

    public static Vec operator *(Vec right, Vec left) { return new Vec(right.X * left.X, right.Y * left.Y, right.Z * left.Z); }

    public static Vec operator *(Vec right, double left) { return new Vec(right.X * left, right.Y * left, right.Z * left); }

    public Vec GetNormal() { return this * (1 / Math.Sqrt(X * X + Y * Y + Z * Z)); }

    public double DotWith(Vec b) { return X * b.X + Y * b.Y + Z * b.Z; }

    public Vec CrossWith(Vec b) { return new Vec(Y * b.Z - Z * b.Y, Z * b.X - X * b.Z, X * b.Y - Y * b.X); }
}

Raytracer 光反射错误

Raytracer light reflection bug

c#

c++

raytracing