Ray Tracing Basics

Yesterday I finished some React challenges from the bootcamp I’m doing. I also learned about Bounding volume hierarchy and The Rendering Equation.

A Bounding volume hierarchy is a tree structure that delimits the objects we need to render in a scene. Each node in this tree is either an object that we might have to render, or a virtual object that contains more than one object.

If we cast a ray and we hit a node in the tree we know we only have check if the ray hits any of the objects below that node, reducing the amount of objects we need to check. This basic optimization drastically increases performance as the scenes have more objects and as the objects become more complex (with different textures and polygons).

The Rendering Equation is a simple but complete model of how ray-tracing works:

The Rendering Equation

The term on the left

Total spectral radiance term

represent the spectral radiance of an arbitrary ray we cast. In computer terms the spectral radiance is pretty much the rgba, the hue we calculate for the ray. The aim of a ray-tracing engine is to solve for this hue for each pixel on a canvas/screen.

The first term on the right

Emitted spectral radiance term

is called the emitted spectral radiance, which is basically the ambient light.

The second term on the right

Integral over unit hemisphere term

represent the the entire interaction between the ray and the surface it’s trying to render. There’s a lot of interesting physical phenomena that this term takes into account:

  • the incidence of the ray with the normal of the surface at the point of intersection

    Weakening factor term

    which reduces the overall radiance as the angle increases.

  • the amount of light reflected back to origin of the ray at the point of intersection

    Incoming spectral radiance term

    which in itself is another ray-tracing problem. There’s usually a lot of recursion and parallelism in ray-tracing engines.

  • the bidirectional reflectance distribution function

    Bidirectional reflectance distribution function term

    is basically how we account for light effects on different surfaces: glossy, mirror reflections, matte/not glossy, and others.

Today I’m gonna do some Node and Elixir Challenges from my bootcamp. I wanna get those out of the way quickly and start focusing on the Ray Tracer.

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