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How do you figure out how much area other patches are taking up in the view of the emitting/reflecting patch?

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I think there are two parts to this.

-the simple one is, you calculate the area of the patches, multiply by the cos of the angle between the normal and the direction to the emitting one and by the cos of the angle between the normal of the emitting one and the direction to the patches. that divided by the square distance*pi and you know how much proportional area of the emiting patch is occupied by every other patch. (this is called the 'view factor' or also 'form factor').

this would work nicely in object that cannot occlude.

-the more complex solution is to discover occlusion. there are a view techniques.

a) you trace rays between patches to figure out if there is something inbetween occluding those

b) you trace several rays between patches to also figure out how much occlusion happens, (I've done it that way here: http://twitpic.com/4khy8e )

b) you render the scene from the point of view of every patch and accumulate the energy of every rendered pixel (in that case you might not need to care about individual patches), that's quite nicely described in: http://freespace.virgin.net/hugo.elias/radiosity/radiosity.htm

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