# Ray Cylinder Intersection in Optix?

I’ve been modifying the tutorial examples recently and I’ve had some trouble getting cylinder intersection to work. I rewrote the code provided for sphere intersection to make it more general and have succeeded in getting it to work for spheres. For some reason, my cylinders don’t seem to work. I have pasted my intersection code below - it is quite simple:

float3 O = ray.origin - center;
float3 D = ray.direction;

float a = D.x * D.x + D.z * D.z;
float b = 2*(O.x * D.x + O.z * D.z);
float c = (O.x * O.x + O.z * O.z) - radius*radius;

float disc = bb-4a*c;

float3 hit_p, offset;

if(disc > 0.0f) {
float root1, root2;

``````float sdisc = copysign(sqrtf(disc), b);
float q = (-b - sdisc) / 2.0;

root1 = q / a;

if (q != 0) {
root2 = c / q;
}
else {
root2 = root1;
}

if (root1 < 0) root1 = root2;
if (root2 < 0) root2 = root1;

float final_root = min(root1, root2);
float3 hit_p  = ray.origin + final_root*D;
float3 dummy_normal = hit_p;

dummy_normal.y = 0;
dummy_normal = normalize(dummy_normal);

if( rtPotentialIntersection( final_root ) ) {