Similar to how an artist composites an scene layer by layer, a ray-tracer can be built up by adding simple operations...

Ambient color of object

Diffuse color of object using surface normal

Directional Lights

Reflections

Shadows

Anti-Aliasing Multi-Sampling: None

Anti-Aliasing Multi-Sampling: 1x

Anti-Aliasing Multi-Sampling: 2x

Anti-Aliasing Multi-Sampling: 4x

Anti-Aliasing Multi-Sampling: 5x

Anti-Aliasing Multi-Sampling: 9x

Anti-Aliasing Multi-Sampling: 16x

Refraction

Planar Texture Mapping with Bi-Tangents