The Ray Tracer Challenge

Identifying Hits

When rendering your scene, you’ll need to be able to identify which one of all the intersections is actually visible from the ray’s origin. Some may be behind the ray, and others may be hidden behind (or occluded by) other objects. For the sake of discussion, we’ll call the visible intersection the hit. This is really the only intersection that matters for most things.

The hit will never be behind the ray’s origin, since that’s effectively behind the camera, so you can ignore all intersections with negative t values when determining the hit. In fact, the hit will always be the intersection with the lowest nonnegative t value.

Joe asks:

Why do I have to keep all the intersections?

You just read that you can ignore all intersections ...