Light and Shadow
- local illumination
is handled by material and volume shaders by computing the color of an illuminated surface or volume simply by considering the direction, strength, and color of incoming light and how it is reflected towards the viewer. Incoming light always comes directly from the light source (which can optionally be blocked by occluding objects, causing shadows). The examples in chapter 4.1 on page 46 demonstrate various kinds of local illumination.
- global illumination
complements local illumination by allowing material shaders to take into account indirect illumination from other lighted objects in the scene. It cannot be computed by directly adding up incoming light from light sources but requires a special preprocessing step that emits photons from light sources and follows them as they bounce around in the scene. This allows simulating natural effects that go far beyond local illumination. Global illumination is described in chapter 7.6 on page 173.
KeywordsSpot Light Shadow Casting Occlude Object Point Light Global Illumination
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