Unity 5 includes Enlighten, a real-time global illumination solution from Geomerics.
You can use Enlighten for baking light maps, light probes, and for
real-time indirect lighting. This works both in real-time in a game, and also in the
Unity 5 editor on many of the platforms supported by Unity. These include Windows, OS X,
iOS and Android.
The core of Enlighten is a real-time radiosity engine. It generates a light
map containing only the indirect lighting, that is, the light that is bounced off
surfaces back into the scene. The following figure shows this:
The left scene is illuminated by direct lighting, with no bounce light
and no added ambient light term. Any surfaces in shadow are black.
The middle image shows the same scene and lighting setup with only the
indirect light contribution and no albedo textures applied. This is the output Enlighten
generates in real-time.
The right image shows the final composition that you normally see in a
Enlighten calculates the indirect light. The results are stored in a
light map or in light probes, and applied in the shader code. The standard Unity
materials all make full use of Enlighten and this applies fully to custom material
shaders. The shaders and the Unity rendering engine also ensure the direct light is
properly rendered, so that the final game looks like the final composition.