AO ignoring alpha channels

[ABK]

Hi everyone

 

Does anyone no a way of getting ambient occlusion to ignore alpha channels in it's calculations?

 

In short, a lot of my work needs graphics that go over walls, surfaces in my scenes. I do this by creating planes and positioning the planes as required. This works well as a flexable technique but has the unfortunate side effect of forcing me to turn AO off all my surfaces - otherwise I get a series of black squares underneath each plane.

 

I have attached an example showing the problem. In the shots the cross is an alpha on a plane positioned over a floor with a white AO shader on. I have tried using the 'return occlusion in alpha' check box to little effect.

 

Any ideas?

 

 

Antony