Indirect Lighting in 3-D Video Games

Ke Xu

Game designers have devised an ingenious algorithm to reproduce indirect lighting effects in virtual 3-D environments. Ke Xu describes the reflective shadow map.


figureA light map applied in The Last of Us captures indirect lighting: Direct sunlight hits only part of the left wall; the right wall picks up sunlight scattered from the left.

Injecting reality into virtual reality is harder than it might seem, especially when it comes to lighting. Until recently, 3-D video games only simulated the effects of direct lighting. That is, objects were illuminated by artificial sources that simulate real-world counterparts: the sun, street lamps, flashlights, etc. However, in the real world, light from direct origins is scattered, adding countless indirect sources to the surroundings. The subtleness of indirect lighting is crucial to creating realistic effects.

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