View Full Version : mia_material and alpha issue

09 September 2007, 01:05 AM
i'm trying to get an mia_material to not show up in an alpha channel render (like when matte opacity is set to zero for a maya shader).

it has textured transparency (using cutout opacity).... pass custom alpha is enabled in globals (there are other mia shaders in the scene which need it checked). must be rendered all in one pass.

this is probably really simple and i'll kick myself when i find out but i have to work on to other projects so will do the lazy thing and ask here :)

09 September 2007, 02:11 AM

try turning "propagate alpha" on

09 September 2007, 02:25 AM
tried it both on and off, but anyway propogate alpha just enables textured alpha but doesn't control the alpha as a whole (can't influence the matte/opaque areas) so that wouldn't work.

in theory disabling pass custom alpha would work but that would ruin the rest of the scene.

09 September 2007, 09:57 PM
sorry, i was in a hurry yesterday and actually I've read "how to show alpha" instead of "not to show alpha".

Independently of any mia issue in your scene, you can simply setup a mask pass for your render, only with black and white surface shaders wherever you want them (then use this render acting as an alpha mask in post).

You can also try typing a value of 0 in th cutout opacity or doing a custom cutout map if you really want to keep everything in one render.


mr Bob
09 September 2007, 10:52 PM
This is just another example of the mess that maya and Mental Ray are....

The way round it is create a lambert shader set all tha values to zero , in the attribute editor go to the lambert shaders , shading group, open up the MR tab , then drag your MR shader into the material slot. Apply your material and then you should get your correct alpha ....


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09 September 2007, 10:52 PM
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