Indirect lighting in Zilch takes the form of image-based lighting, where an image--primarily a skybox--provides environmental ambient lighting throughout a scene. Whether a skybox is artist-created or derived from HDR images, is often used to give a scene an ambient light associated with a certain time of day (e.g. dusk, noon, dawn) or certain types of weather (e.g. clear skies, threatening clouds). In the case of interior scenes, it may just provide a static ambient light so that no matter where in the scene a player is, objects maintain some level of visibility.

When using a skybox, it may be either visible, providing a static background for a scene (e.g. clouds in a sky) or invisible, in which the skybox provides ambient light for an interior scene (e.g. a cave that needs to have a constant source of ambient light not provided by deferred or forward renderer.

NOTE: If a skybox is used and is visible, MipMapping on the skybox TextureBuilder ContentComponent must be set to PreGenerated.

When applying indirect lighting to scene, the math used is the same as is used when applying direct lighting. The only difference between the two is that much of the math is pre-calculated for indirect lighting.