View Full Version : 3dsMax using ambient occlusion to determine how a surface recieves light.

08-22-2011, 05:20 PM
Long topic field I know.
I was wondering if there is a way to use ambient occlusion to determine how much a surface can be lit?

For example, if I wanted to use a falloff map that uses the light and shadow functionality; could I use and ambient occlusion map or material to determine how much light will affect the falloff map?

EDIT: I just noticed the spelling error in the subject field but am powerless to correct it.

08-22-2011, 11:17 PM
Do you mean like putting the AO map as the specular power? It could cause some shading irregularities as the light passes around and should be lighting areas, but it's the closest thing I can think of to what you want.

That might throw off the lighting to the extent it could fake a change to the ramp.

08-23-2011, 12:26 AM
Good idea, however it didn't work :(.

The idea is to cause the fall off map to read the dark areas of the ambient occlusion maps as area's that light will not hit and then render the shadow and light map accordingly.

If that doesn't work out, is there any way to change the ramp of the ambient occlusion render to make it not render out any gray but instead; black or white?

08-23-2011, 01:05 AM
So you want some areas that don't respond to any light and don't cast shadows?

Why not have the whole thing with bits you want lit and don't want lit as one object, and make the bits you don't want lit or casting shadows as transparent.

Then, have a second object that doesn't cast shadows and is unlit, as the parts you want not affected by the light.

That way the unlit parts (marked as transparent in object 1) won't cast shadows or recieve lighting, but the rest will behave with the ramp. And part 2, will be unlit, will be unaffected by the ramp.

Also, Ctrl+L in Photoshop on the AO bake, you should be able to move the tiny arrowheads around (toward the center for both of them).

08-23-2011, 02:37 AM
Not sure if I understand you correctly, but I would just put the AO Map in the white slot of the falloff (if the falloff is to be b/w), or use it as a mask in a Mix Map (if the colors of the falloff are different).

08-23-2011, 07:06 AM
I forgot to say thank you earlier for your responses. I'm going to take these ideas into consideration to see what I can do.
The reason I wanted to use ao to determine what isn't lit is I'm dealing with debris and hundreds of little objects and wanted the cracks between them to be accented within the color scheme I created from the falloff maps.
Your current suggestions have given me some ideas that I'm minutes from implementing.

Once again, thanks for giving my post some attention and the ideas. I'm very grateful.