Raytracing

Raytracing

Raytracing is a rendering technique that simulates the way light travels in the real world. Instead of processing polygons line by line like scanline rendering, raytracing shoots rays from the camera through each pixel and calculates what they hit. When a ray hits a surface, the renderer calculates the color based on the material and then shoots additional rays for reflections, refractions, and shadows.

The basic raytracing algorithm is surprisingly simple. For each pixel in the image, you shoot one or more rays from the camera position through that pixel into the scene. You find the first surface that each ray hits. Then you calculate the color at that point by evaluating the material and the lighting. For reflective surfaces, you bounce the ray and continue. For transparent surfaces, you refract the ray and continue.

Raytracing naturally handles effects that are difficult with scanline rendering. Reflections are accurate because the ray bounces off the surface at the correct angle. Shadows are accurate because the renderer checks if a light source is visible from the surface point. Refractions through glass and water work correctly. The result is much more realistic than scanline rendering, especially for scenes with complex lighting.

The downside of raytracing is performance. Shooting rays for every pixel, and then shooting more rays for reflections and shadows, requires enormous computational power. Early raytraced images took hours to render even for simple scenes. Modern hardware with dedicated ray tracing cores, like Nvidia RTX, has made real time raytracing possible, but it is still more expensive than traditional rasterization.

Raytracing is the foundation of most modern VFX renderers. Arnold, RenderMan, V-Ray, and Cycles all use raytracing as their core algorithm. The difference between them is in how they optimize the ray tracing process, how they handle multiple bounces, and how they reduce noise. But the fundamental concept of shooting rays from the camera is the same across all of them.