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Global Illumination

Global Illumination (GI) is a set of techniques intended to simulate realistic light propagation in a virtual environment.

The following comparison shows the use of global illumination in a scene with two light sources: a red Omni Light and a World Light, volumetric sun shafts included.

The left image shows the scene illuminated with direct light only, so that we see only silhouettes of unlit objects and a large number of details is hidden in the darkness.

The right image shows the scene with both direct and indirect light, which makes it look way more realistic and consistent.

UNIGINE provides both realtime and precomputed solutions for GI simulation.

See Also#

Static GI#

Static Global Illumination is mainly applicable to static unchanging environments and implies baking of lighting in order to drop expensive calculations and keep the performance high.

Light Baking#

The computation of indirect lighting is a very expensive task for the processing unit, so it is usually performed once at the development stage (lighting is baked) and the results are used later for static lighting at run time.

Light Baking is the way of precomputing and storing data that describes how light rays bounce around static geometry causing indirect lighting. Adding indirect lighting to modelling helps significantly improve the realistic look of the scene.

The Bake Lighting window provides the interface to light baking inside UnigineEditor.

The following approaches are available:

Lighting from all types of Light Sources is baked, however, note that both direct and indirect (bounced) light is baked from emissive objects, while light sources provide only indirect light for baking and are to be kept enabled to provide direct light and specular highlights.

Modes of Light Sources#

Omni, Projected, and World light sources have the Mode parameter that defines their contribution to the light baking process and determines if shadows are to be baked.

The following modes are available:

  • Dynamic. The light source provides direct realtime lighting only. It is considered disabled while light baking is being calculated, that is why the scene remains unlit when the light is turned off after light baking. No shadows are baked.
    Dynamic light source enabled. No GI is baked.
    Dynamic light source disabled.
  • Static. The light source contributes to light baking and remains enabled all the time providing direct realtime lighting while the indirect light is being baked. When lighting is baked, such light sources are not to be moved; otherwise, this option can cause a lack of physical accuracy registered by the eye. Shadows for Omni, Proj, and World lights are baked.
    Static light source enabled.
    Static light source disabled. Indirect light is baked.

Realtime GI#

For scenes that have moving light sources and changing environment, baking of lighting is inappropriate. The following realtime approaches of GI simulation are provided in UNIGINE.

  • Ambient lighting from dynamic environment probes.

  • The SSRTGI (Screen-Space Ray-Traced Global Illumination) technology is a set of screen-space ray tracing techniques for GI simulation with the real-time performance level. It incporporates Screen-Space Ambient Occlusion, Screen-Space Global Illumination and Bent Normals features. The technology doesn't require light baking, so every object and light source can be freely moved.

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Last update: 2020-10-13