Geomerics - Advancing Technology Through Innovation

What does Enlighten do?

Current game lighting technology requires a large number of lights. Artists use additional lights to fill in areas that, in reality, are lit by light reflected off other surfaces in the scene. With dynamically computed radiosity one can achieve far greater realism with only a handful of light sources. Enlighten brings truly real time dynamic lighting to this generation of game development - a world first. By removing the need for artists to painstakingly mimic realistic lighting, time to create artwork is dramatically reduced. And with frame rates over 100fps Enlighten can be incorporated into any game setting.

What is radiosity / global illumination?

Roughly speaking, whenever light strikes a surface it is either reflected like a mirror, or absorbed then partially re-emitted. Surfaces that mostly reflect light appear shiny and we say they are highly specular. Surfaces that absorb and re-emit light appear matte and look the same regardless of what angle you look at them from. This is because they re-emit the light away from them in all directions, whereas specular surfaces tend to reflect the light as if the light was a ball that bounced off. Mostly matte surfaces, such as chalk or paper, are said to be highly diffuse. The colour of a diffuse surface actually comes from the spectrum of light it re-emits.

The reflection of light (specular) and the absorption then re-emission of light (diffuse) both effectively bounce some light back into the scene. This fact of life is typically ignored in most games lighting models because it massively increases the complexity of the computations. The reflected light could then strike another surface, where another portion of it may be bounced. This process of light bouncing continues until all light has been fully absorbed or reflected out of the environment.

Strictly speaking, 'radiosity' models the bouncing of light from just diffuse surfaces. If we added to this mix the specular bounces and more complex behaviours of light such as the ability to focus through glass, form rainbows, and be scattered in media such as fog then we begin to approach the realm of physically accurate 'global illumination'. In essence, this is computing a physically correct lighting model for the entire world. In the domain of the high-end renderers used in the CGI and film industries, accurate solutions that include all these complex effects can take hours (or even days) to compute and hence are currently out of the range of the processing power available to games without some form of compromise.

Enlighten is a radiosity solution that also supports convincing specular highlights from bounced specular lighting. It is therefore somewhere between a pure radiosity solution and a fully accurate global illumination solution, and focused on meeting the needs of next-gen game lighting. We refer to it as a radiosity solution for simplicity.

This image gives a comparison between direct illumination from a point light source (the sun) and a radiosity solution which treats the sun as an area light source. All surfaces are assumed to be purely diffuse. Note that even in this simple model the bounced light makes an enormous difference to the mood and believability of the scene

So, radiosity fully models the subtle effects arising from the diffuse inter-reflections of light between surfaces, and it dominates many real-world situations. Harsh shadows are filled in by light reflecting from bright areas, and the mood of a room is heavily influenced by the colours of the walls, a red wall makes the room feel warm and welcoming, a blue wall makes it feel cold and menacing.

The potential artistic freedom of real-time radiosity

The ability to compute radiosity effects in real time breaks a whole array of restrictions under which games are currently made. Without real-time radiosity the diffuse lighting solution is often computed off-line and layered on top of the geometry as a light-map. Then if a light is turned on, or the sun is obscured, nothing happens! A noticeable example of this is when one is exploring scenes set in a dark room with a torch. In reality we know how exploring such a room will still allow us to see objects outside the torch light due to bounced light, but in practice games cannot traditionally achieve this effect.

The ability to move lights around and rapidly see the effects on the world frees up artists to be far more creative. Instead of being restricted to a limited set of lights and, typically, a limited colour palette as well, artists will be able to apply bright neon area lights and immediately explore the consequences for the look of a world. They will be able to change the texturing of the environment and immediately see the impact upon the lighting.

In truth, we can't predict the impact real time radiosity will have on our artists. Real time radiosity lighting has never been possible before, in any computing industry. However, we can be certain that there will be many so far unthought-of exciting possibilities that come from real time radiosity lighting!

What do we mean by 'real time'?

The phrase "real-time radiosity" is both over-used and abused in the graphics literature. For use in a game, computing radiosity at 10 frames per second (fps) is simply not good enough. For a lighting technique to be practical then in isolation it must be hitting well over 100fps, so that when it is incorporated into a complete solution, rates of 60fps can be achieved. Enlighten easily fulfils these performance requirements.