ray tracer objects stretch when off center

Question

I am writing a ray tracer program for my computer graphics class. So far I only have spheres implemented and a shadow ray. The current problem is that when i move my sphere off center it stretches. here is the code that i use to calculate if a ray is intersecting a sphere:

bool Sphere::onSphere(Ray r)
{
    float b = (r.dir*2).innerProduct(r.pos + centre*-1);
    float c = (r.pos + centre*-1).innerProduct(r.pos + centre*-1) - radius*radius;
    return b*b - 4*c >= 0;
}

here is the code that i use to spawn each ray:

for(int i = -cam.width/2; i &lt cam.width/2; i++)
    {
        for(int j = -cam.height/2; j &lt cam.height/2; j++)
         {
            float normi = (float)i;
            float normj = (float)j;
            Vector pixlePos = cam.right*normi + cam.up*normj + cam.forward*cam.dist + cam.pos*1;
            Vector direction = pixlePos + cam.pos*-1;
            direction.normalize();
            Vector colour = recursiveRayTrace(Ray(pixlePos, direction), 30, 1, 0);
            float red = colour.getX()/255;
            float green = colour.getY()/255;
            float blue = colour.getZ()/255;
            fwrite (&red, sizeof(float), 1, myFile);
            fwrite (&green, sizeof(float), 1, myFile);
            fwrite (&blue, sizeof(float), 1, myFile);
        }
    }

recursiveRayTrace:

Vector Scene::recursiveRayTrace(Ray r, float maxDist, int maxBounces, int bounces)
{
    if(maxBounces &lt bounces)
        return Vector(0,0,0);
    int count = 0;
    for(int i = 0; i &lt spheres.size(); i++)
    {
        if(spheres.at(i).onSphere(r))
        {
            Vector colour(ambiant.colour);
            for(int j = 0; j &lt lights.size(); j++)
            {
                Vector intersection(r.pos + r.dir*spheres.at(i).getT(r));
                Ray nRay(intersection, lights.at(i).centre + intersection*-1);
                colour = colour + lights.at(i).colour;
        }
        return colour;
        }
    }
    return Vector(0,0,0);
}

What i get is an sphere that is stretched in the direction of the vector from the center to the center of the circle. I'm not looking for anyone to do my homework. I am just having a really hard time debugging this on. Any hints are appreciated :) Thanks!

Edit: cam.dist is the distance from the camera to the view plane

Answer 1

The stretching is actually a natural consequence of perspective viewing and it is exaggerated if you have a very wide field of view. In other words moving the camera back from your image plane should make it seem more natural.