Algo - Ray tracing : spheres like eggs

Question

I am currently working on a project called "Raytracer" in c. I encounter a problem, the spheres are oval when they are not centered.

Here is an excerpt of my code:

int           i;
int           j;
t_ray         vect;
i = -1;

vect.x = 100. - cam.x;

while (++i < screenx)
{
    j = -1;

    vect.y = ((screenx / 2.) - i - cam.y) * -1.;

    while (++j < screeny)
    {
        vect.z = (screeny / 2.) - j - cam.z;
    }
}

Answer 1

This is likely not a bug, but simply a reality of how perspective projections work. When the camera is directly looking at a sphere, the projection is circular, but as it moves away from the center, it distorts. For more info read this link in the POV-Ray wiki: http://wiki.povray.org/content/Knowledgebase:Misconceptions#Topic_3

Answer 2

In that way the vector has different length on different pixels. You should normalize the vector at the end (dividing the components by the vector length)

Answer 3

It's probably late now, but to give you an answer, your "problem" is in reality called "fish-eye". I encounted this problem too. there're many ways to avoid this problem. The easiest is to increase the distance between the camera and your scene. It's not the cleaner way.

You also can normalize your rays, here are some reasons :

.keep the same distance ratio for every rays

.keep the same angle difference between every ray and its neighbors

.it makes many intersection computations ways easier