Recursive Ray Tracing

Ray Tracing:

Recursive

• Eye-screen ray is the primary ray
• Backward tracking of photons that could have arrived along primary
• Intersect with all objects in scene
• Determine nearest object
• Generate secondary rays
  • to light sources
  • in reflection-associated directions
  • in refraction-associated directions
• Continue recursively for each secondary ray
• Terminate after suitably many levels
• Accumulate suitably averaged information for primary ray
• Deposit information in pixel

Ray Casting:

Non-recursive

• As above for ray tracing, but stop before generating secondary rays
• Apply illumination model at nearest object intersection with no regard to light occlusion
• Ray becomes a sampling probe that just gathers information on
  • visibility
  • color