AWS Thinkbox Discussion Forums

Matt object, animated cut out alpha


I’m trying to compose krakatoa rendere over a Matt object.
I need the Matt object to be gradually formed. I used a simple ramp and assigned it to the cut out (alpha or transparency) of the material.
but krakatoa always renders the whole Matt object and doesn’t respect the cut out part of the Matt object.

is there any way to do this using Magma?

thank you in advance.

It would be great If I can handle this sort of Matt objects.
please help if you can.
thank you very much.


In the current implementation of Krakatoa MY, we don’t take the Alpha of the mesh based on a cutout texture in account. We do support that in Krakatoa MX though, so we have some experience with it. We could try to implement the same kind of texture cutout support in KMY, but first we need to know more about your case.

In general, the way compositing of semi-transparent mattes with particles is done is this: Particles behind the Matte object are sent to a background layer, particles in front are left in the beauty RGBA channel. You then render the matte object in another renderer and composite the Krakatoa RGBA over the other renderer’s output of the Matte object, over the Background layer. This way, the rendered object in between reveals background particles through its Alpha, and foreground particles are unaffected because they are on a layer over that. Of course, this works only with simple objects and does not support multiple meshes with multiple layers of transparency and particles enclosed between them. … nd-mattes/

If your cutout has zero alpha in some areas, it really does not matter whether the particles in it were sent to the Foreground or Background layer - they would still appear in the final composite.

So in the simplest case of a plane with a cutout texture on it, while your whole plane would matte out particles, as long as you send the occluded particles to the background layer and composite the three images (two Krakatoa, one other renderer between them) in post, you should get a valid result.

Can you explain or post screenshots of what your setup / Matte object looks like?

so no more experience for me, that is good :slight_smile:

yes, and basically, the old school layer rendering, I think is simple and efficient.
I’m not quite clear about the situation I should face in my project, but I guess It wouldn’t be so easy.
I hope the traditional layer rendering would work for this situation.

thank you again.

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