Tracking Intersections

The Ray Tracer Challenge — by Jamis Buck (35 / 108)

👈 Intersecting Rays with Spheres | TOC | Identifying Hits 👉

Currently, your intersect function returns a set of t values, but imagine for a moment a beautifully complex scene, full of spheres, cubes, cylinders, cones and dozens of creative combinations. You cast your ray into that scene and get back a double handful of intersections. You now know where the intersections occurred (thanks to the t values), but you have no idea how to draw them. What object was intersected at that point? What color is it? What are its material properties? Should there be a reflection or not? You just don’t know.

With the addition of one more property, you’ll have the foundation of what you need to answer those questions. You’re going to create a new data structure, called an intersection, which will (for now) aggregate two things:

You’ll add additional properties in later chapters, but these will suffice for now. Go ahead and add the following test to show both how to create an intersection and how its properties are accessed.

You’ll also need a way to aggregate these intersection objects so you can work with multiple intersections at once. (Consider your sphere intersection routine, which can return zero, one, or two intersections.) Write the following test, which introduces a new function called intersections(i1, i2, …). This should return a new collection of the given intersection objects.

This list of intersections could just be an array primitive in your implementation language, but note that you’ll be adding a function shortly (in ​Identifying Hits​) that operates on these lists of intersections.

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