为什么raytracer渲染球体为椭圆形？ [英] Why does raytracer render spheres as ovals?

问题描述

在过去的几天里，我一直在第一次打破光线追踪器。然而，有一些怪癖困扰着我，我真的不知道如何解决。从一开始就一直存在的是场景中的球体形状 - 渲染时，它们看起来像椭圆形。当然，这个场景是有角度的，但最终的形状仍然很古怪。我附加了一个示例渲染，我在图像左下角的反射球上特别看到了这个问题。 b

我不知道可能是什么原因造成的。这可能是射线球交叉点代码，如下所示：

  bool Sphere :: intersect（Ray ray，glm :: vec3& hitPoint）{
 //计算A，B和C系数
 float a = glm :: dot（ray.dir，ray.dir）; 
 float b = 2.0 * glm :: dot（ray.dir，ray.org-pos）; 
 float c = glm :: dot（ray.org-pos，ray.org-pos） - （rad * rad）; 
 
 //查找判别式
 float disc = b * b  -  4 * a * c; 
 
 //如果判别式为负数，则没有真正的根，因此返回
 // false，因为光线未命中sphere 
 if（disc <0）
返回false ; 
 
 //计算q 
 float distSqrt = sqrt（disc）; 
 float q; 
 if（b <0）
 q =（ -  b  -  distSqrt）/2.0; 
 else 
 q =（-b + distSqrt）/2.0; 
 
 //计算t0和t1 
浮动t0 = q / a; 
 float t1 = c / q; 
 
 //确保t0小于t1 
 if（t0> t1）{
 //如果t0大于t1将它们交换
 float temp = t0; 
 t0 = t1; 
 t1 = temp; 
} 
 
 //如果t1小于零，则该物体处于光线的负方向
 //，因此光线会遗漏球体
 if（t1 < 0）
返回false; 
 
 //如果t0小于零，交点在t1 
 if（t0 <0）{
 hitPoint = ray.org + t1 * ray.dir ; 
返回true; 
} else {//其他交点在t0 
 hitPoint = ray.org + t0 * ray.dir; 
返回true; 
} 
} 
  

或者它可能是另一回事。有人有想法吗？非常感谢！

解决方案

看起来您正在使用非常广泛的 field of view （FoV）。这产生了鱼眼镜头的效果，扭曲了画面，尤其是对边缘。典型的例如90度（即任一方向45度）给出了一个合理的图片。

折射实际上看起来相当好，它是倒转的，因为折射率非常高。美丽的图片在这个问题。

I've been hacking up a raytracer for the first time over the past few days. However, there are a few quirks which bother me and I don't really know how to work out. One that has been there since the beginning is the shape of spheres in the scene - when rendered, they actually look like ovals. Of course, there is perspective in the scene, but the final shape still seems odd. I have attached a sample rendering, the problem I have is especially visible on the reflective sphere in the lower left part of the image.

I don't really know what could be causing this. It might be the ray-sphere intersection code which looks as follows:

bool Sphere::intersect(Ray ray, glm::vec3& hitPoint) {
//Compute A, B and C coefficients
float a = glm::dot(ray.dir, ray.dir);
float b = 2.0 * glm::dot(ray.dir, ray.org-pos);
float c = glm::dot(ray.org-pos, ray.org-pos) - (rad * rad);

// Find discriminant
float disc = b * b - 4 * a * c;

// if discriminant is negative there are no real roots, so return
// false as ray misses sphere
if (disc < 0)
    return false;

// compute q
float distSqrt = sqrt(disc);
float q;
if (b < 0)
    q = (-b - distSqrt)/2.0;
else
    q = (-b + distSqrt)/2.0;

// compute t0 and t1
float t0 = q / a;
float t1 = c / q;

// make sure t0 is smaller than t1
if (t0 > t1) {
    // if t0 is bigger than t1 swap them around
    float temp = t0;
    t0 = t1;
    t1 = temp;
}

// if t1 is less than zero, the object is in the ray's negative direction
// and consequently the ray misses the sphere
if (t1 < 0)
    return false;

// if t0 is less than zero, the intersection point is at t1
if (t0 < 0) {
    hitPoint = ray.org + t1 * ray.dir;
    return true;
} else { // else the intersection point is at t0
    hitPoint = ray.org + t0 * ray.dir;
    return true;
    }
}

Or it could be another thing. Does anyone have an idea? Thanks so much!

解决方案

It looks like you're using a really wide field of view (FoV). This gives the effect of a fish-eye lens, distorting the picture, especially towards the edges. Typically something like 90 degrees (i.e. 45 degrees in either direction) gives a reasonable picture.

The refraction actually looks quite good; it's inverted because the index of refraction is so high. Nice pictures are in this question.

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