reflection driving the opacity map

[gpapaioa]

Hello ppl

 

My case is the following: i am matching a real mirror like surface with a CG one. In my scene, other CG geometry is reflected and I want to comp this reflection pass to the real plate. But because of the alpha I get black wherever there is nothing reflected (as expected). I tried to do a luma key in Nuke but doesn't work very good with the edges, due to the fact there are volumes involved. Does anyone know if its possible to make the reflection drive the opacity so whenever there is nothing reflected, alpha will turn to black? Thank you.

[xray]

This is a bit of a hack I think...

 

Check to see if the length of the color of the reflection is greater than zero and send the result to the Alpha in the shader.

 

Here's an example. 

alphaRefl.hip

[gpapaioa]

Thank you very much this is exactly what I was looking for. I must study about CVEX and custom shaders. 

[fathom]

the "trace" vex operation will return color and opacity (and alpha) from the traced vector.

[gpapaioa]

I am now experiencing another problem. Since I want only object reflection and not light reflection, it seems that i get reflection only from smoke and not from fire. Is there a solution for this? I assume it happens because the Pyro Shader treats fire like emission. Here's a still, the explosion is reflected on the glass building

 

[gpapaioa]

[sOLVED] the Emission Illuminates Object on the Pyro Geometry node was uncheck by default  . So Emission wasnt calculated on the secondary rays.

Edited September 7, 2014 by gpapaioa