File:Recursive raytracing.svg

Idea of recursive raytracing.

The sample 3D scene has two lights and 3 objects:

1. a - oval: nontransparent, nonreflecting
2. b - sphere: transparent and reflecting
3. c - cube: nontransparent, but reflecting

Observer (camera) is placed at point O. Primary ray (green) is emited from O and hits object b. Since this object reflects and refracts light two secondary rays are emitted from hit point: red for reflected and blue for refracted ray. Reflected ray hits object a and none secondary rays are emitted. Refracted ray hits object b and is refracted one more time (reflected ray hasn't been show, however it should be emitted too). This ray hit object c and just one reflected ray is emitted. It do not hit any object and recursion stops.

Thin dashed lines are shadow rays - additional rays use to determine visibility of light: object b occlude light L1 when point on b is shading, when point on a is shading, object blocks light L1.

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