The rendering time for a ray tracer depends on the number of ray intersection tests that are required at each pixel. This is roughly dependent on the number of primitives in the scene times the number of pixels. Early on, significant research effort was spent developing methods for accelerating the ray-object intersection tests.

We've already discussed object-dependent optimizations to speed up the sphere-ray intersection test. But more advanced methods are required to make ray tracing practical.

Among the important results in this area are:

• Bounding Volumes
• Spatial Subdivision
• Light Buffers