PGR3 update

[Laa-Yosh]

You can calculate an occlusion map in pretty much every 3D art package nowadays. With some advanced renderers, you can even distribute it to a network of computers, although the average time shouldn't be more than a few hours per car or other object. I don't really get why they should use a dirt map...

 

[Brimstone]

In reality, the level of ambient light is not constant. For example, if the sun is behind heavy cloud, then the level of light in the middle of an open field will be greater than that in an alley-way. This is because the buildings either side of the alley-way occlude the sky (i.e. block out some of the light). This ambient occlusion value can be calculated in our lighting tool and stored per-vertex on the models. The first screenshot shows a car wheel with no ambient occlusion (i.e. constant level of ambient light). The second pic shows the same wheel with the intensity of the ambient light from before turned down on a per-pixel basis, depending on the ‘up’ direction at that pixel (upwards facing pixels are lighter than downward facing ones). Finally, the third picture is the full monty. This one takes into account the ambient occlusion that results from the wheel itself, so the disc and bits behind the spokes have an even lower level of ambient light because the spokes themselves block out light.

I was pretty sure Laa-Yosh said there was no way ambient occlusion could be done on realtime applications on present or near future architecture... Not saying the guy's lying, i'm saying that it's quite impressive

In Time magazine, with Bill Gates and the X-Box 360 on the cover, ambient light was mentioned.

In the Xbox 360 version, Call of Duty 2, the game play is a startling leap forward...Clouds of dust and smoke float up and block the sun, interfering with the ambient light--war is finally getting its fog. The chaos is astonishingly visceral...

 

[Gollum]

In Time magazine, with Bill Gates and the X-Box 360 on the cover, ambient light was mentioned.

Its getting difficult when general terms, technical terms and PR are thrown together. Just because the word ambient appears in all, doesn't neccessarily mean the items are related. So I'll attempt a quick breakdown.

The first screenshot shows a car wheel with no ambient occlusion (i.e. constant level of ambient light).

Like he said, ambient lighting is typically a constant value that gets added to a surface's brightness (diffuse) channel. Its the oldest and least satisfying way to do indirect/environmental lighting. Its still common in games, in CG its often the first thing an artist switches off (using fill lights and/or radiosity instead), as it tends to look very flat and unrealistic.

The second pic shows the same wheel with the intensity of the ambient light from before turned down on a per-pixel basis, depending on the ‘up’ direction at that pixel (upwards facing pixels are lighter than downward facing ones).

Sounds like a simple background radiosity hack - the diffuse is adjusted according to the pixel's normal direction. Probably based on some sort of ramp/gradient and, judging from the description of their lighting tool, going to adjust according to the surroundings. If done properly this can add a lot to the lighting quality.

Finally, the third picture is the full monty. This one takes into account the ambient occlusion that results from the wheel itself, so the disc and bits behind the spokes have an even lower level of ambient light because the spokes themselves block out light.

Ambient occlusion is quite different from amient light in that it simulates some of the effects of radiosity (its basically a hack ). In CG, an ambient occlusion shader determines how accessible a surface is and adjusts the diffuse value accordingly. Usually this is done by shooting rays at random angles from every pixel, the more rays hit something, the darker the surface will be; the more rays you shoot, the more accurate and less noisy the result. Sophisticated methods require massive amounts of raytracing and are thus unsuitable for real-time 3D. As always, there are other ways to achieve similar results though.

It seems BC's tool pre-calculates one or more ambient occlusion soutions for all of their city/track/car models and stores that information on a per-vertex basis. That way they obviously hope to have more flexible occlusion solutions than by using static textures (needs less RAM and storage space too) and adjust them dynamically while the car is racing along the track. The 3rd image clearly shows that the occlusion, while good looking, doesn't look as detailed as typical pre-baked textures do, but if its dynamic in-game then I guess that more than makes up for it....