# CST 325 – Week 1 – Vectors

It’s the first week of Graphics Programming, and I am really glad to be back to programming after a lack of it in Computer Networks. It has been about a decade since I took a math class, and I have never taken Linear Algebra, so I had to really sit down and talk through the math required for this week.

We are also required to do all the programming assignments with a partner in this class, which is helpful since it forces you to see another’s ideas and talk through points of confusion.

This week we covered vectors, operations on vectors, and how to convert from a vector to a scalar. We also learned how to find the closest point of intersection of a (unit) ray and a sphere, given the distance vector of the ray, the ray’s origin, the sphere’s radius, and the sphere’s center vector. This can be done by using the quadratic formula (after some rearranging of terms to get the equation into a standard form, we can identify each component–a, b, and c).

However, there are cases that we need to catch: when the ray’s point of intersection is opposite the ray’s direction (the result of the quadratic is negative), when the c component of the quadratic is negative (this means that the magnitude of the vector from the ray origin to the sphere center is LESS THAN the radius. In other words, the ray is INSIDE the sphere), and when the discriminant is negative (there are no points of intersection). These three cases should be caught to yield no result.

In our first programming assignment, we implemented a Vector3 class and a Sphere class in order to calculate the nearest points of intersection between a given ray and a sphere (and to catch instances that were invalid).