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Emissive Mapping?

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Hey, I was watching the Unreal 3 video, and I noticed an effect they are doing, which involves parts of the texture being emissively lit. Here's a screeny: Free Image Hosting at www.ImageShack.us So, Is this done with some sort of grayscale emissive map? Thanks

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In my engine the artists have an option to use an "illumination" map.

Normally you do:
Pixel = Albedo * Light

In it's simplest form you can use the illumination map to remove any light contribution using:
Pixel = Albedo * Light * (1 - Illumination) + Albedo * Illumination

It's sometimes desireble to render certain stuff without and light contribution and with the forumla above you've only got to set the illumination value to 1.

I've took it a step further though, basically doing:
RealIllum = Illumination * 8
Blend = Min(1, RealIllum)
Pixel = Albedo * Light * (1 - Blend) + Albedo * RealIllum

If the value for a pixel in the illumination map is between zero and 1/8, the final pixel color blends from the normal lit pixel to strictly using albedo, once it goes beyond 1/8 it becomes brighter and brighter, at most 8x albedo.
I'm using HDR so this will cause a nice glowing effect if set bright enought.
Ofcourse you can choose a different value than 8.

I dunno how Unreal3 does it.

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