Ray Tracer，阴影射线会产生黑圈？

Question

如您在图像中看到的，我在球体的顶部出现了一个黑色圆圈，图像看起来呈颗粒状。它应该更锐利，但是会有这些小的黑白斑点。

这是阴影射线的代码

int pos = 0;

float intersect(const ray &r, vector<unique_ptr<object>> &obj)
{
    //gives closest object hit point and position;
    float closest = numeric_limits<float>::max();
    for(int j = 0; j < obj.size(); j++)
    {
        float t = obj[j]->intersect(r);
        if(t > 1e-6 && t < closest)
        {
            closest = t;
            pos = j;
        }
    }
    return closest;
}
vec color(const ray& r, vector<unique_ptr<object>> &shape,  vector<unique_ptr<Light>> &lighting, int depth)
{   
    vec background_color( .678, .847, .902);
    vec total{0.0, 0.0, 0.0};
    vec ambient{0.125, 0.125, 0.125};

    float t_near = intersect(r, shape);

    if(t_near == numeric_limits<float>::max())
            return background_color;
    else
    {
        total += ambient;
        for(int i = 0; i < lighting.size(); i++){
        total += shape[pos]->shade(lighting[i]->position(), t_near, r);//gives specular + diffuse
        vec shadow_dir = unit_vector(lighting[i]->position() - r.p_at_par(t_near));
        ray shadowRay(r.p_at_par(t_near), shadow_dir);
        float dist = shadow_dir.lenght();
        float a = intersect(shadowRay, shape);
        if(a != numeric_limits<float>::max())
                return vec(0.0, 0.0, 0.0);
        }
        return total;
    }
}

Answer 1

[好的，知道了。

对于黑色圆圈，您必须测试阴影射线的距离，使其小于点与光源之间的距离。同样，对于距离，shadow_dir不应标准化。为了处理阴影交叉点的黑白色斑点，必须将N * bias添加到偏差为1e-4的击中点。偏差不应太小

        vec shadow_dir = lighting[i]->position() - r.p_at_par(t_near);
        float dist = shadow_dir.lenght();
        vec N = unit_vector(shape[pos]->normal(r, t_near));
        shadow_dir = unit_vector(shadow_dir);
        ray shadowRay(r.p_at_par(t_near) + N*1e-4, shadow_dir);
        float a = intersect(shadowRay, shape);
        if(a != numeric_limits<float>::max()){
            float m = shadowRay.p_at_par(a).lenght();
            if(a < dist)
                return vec(0.0, 0.0, 0.0);
            }
        }