====== Global Illumination (GI) ======

===== Description =====

Global Illumination is the collective name for a number of rendering algorithms
that in at least some respect take the entire scene into consideration when doing
lighting computations. There are also [[doc:localillumination|local illumination]]
methods. Aqsis 1.0 is strictly a local illumination renderer, but global illumination
effects can be simulated with very good results.

In a real scene, not only the light sources emit light, but
objects that are illuminated reflect a significant amount of light back into the
scene, and that secondary light can in turn illuminate nearby objects.
This can make some objects appear to take on a tint of the color of nearby
objects, an effect known as //color bleeding//, and light also reaches parts
of the scene that have no direct path to any light source. A very crude but
still quite useful way of simulating at least some of this spreading of light
is to define an //ambient light source//, which illuminates all surfaces in the
scene regardless of their position or orientation.

Shiny objects reflect the scene and each other, not just light sources.
This can be simulated by //reflection maps//.

Ordinary shadows are another effect that require the consideration of more
than the object that is being shaded at the moment. Global illumination models
generate correct shadows as a side effect, while a renderer that does not
use a global illumination model needs to simulate shadows by generating
//shadow maps// in a pre-processing step before the final rendering.

In most scenes, the effects from interactions between objects are pronounced,
and not simulating them will often yield a flat and unrealistic look in a CG image.

===== Requirements =====

  * Aqsis 1.0 and higher have shadow maps, reflection maps and simple ambient light sources.
  * Aqsis 1.0 and higher also implements [[doc:ao|ambient occlusion]], a better but slower simulation of ambient light. 
  * For Aqsis 1.2, support is planned for [[doc:rt|ray tracing]], a true global illumination rendering method.

===== Examples =====