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Brenden Haddad avatar image
Brenden Haddad asked ·

Arnold GPU Rendering with Alpha (Transparency)

Hi, i'm trying to render out an image and it's not carrying the alpha channel and has no transparency in GPU. However, when I switch to CPU it renders properly with alpha. Is this not a supported feature yet?

rendergpualpha for geometrytransparency
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Aaron Ross avatar image
Aaron Ross answered ·

Also, this does not help in the use case where the user wants an environment map to be visible in RGB channels, but invisible to alpha. That's a common scenario, it's the default behavior in 3ds Max, and that's how it works when rendering on the CPU.

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We have a ticket for this issue.

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Aaron Ross avatar image
Aaron Ross answered ·

Thank you, Stephen, that's very helpful. However, this works differently than rendering on the CPU. It should work the same. Users are not going to be able to discover this on their own.

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Stephen Blair avatar image
Stephen Blair answered ·

That's because there's a default background.

If I change the Background to Custom Map and leave the Custom Map slot empty, then I can get the alpha of the objects in the scene.

GPU rendering isn't production ready, it's still in beta.


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Aaron Ross avatar image
Aaron Ross answered ·

Hello... it appears that alpha channel rendering is not supported on the GPU. This is an absolutely critical feature. I was utterly shocked when I discovered that a completely blank 3ds Max scene renders with opaque alpha in Arnold. At first I thought it was just that an environment map was not rendering as transparent alpha. But it does appear that alpha is not supported at all on the GPU.

Please address this issue immediately. It is of absolute top priority. Much higher priority that anything I can think of. GPU rendering is not at all useful for a real production environment if alpha transparency is not supported.

Thank you.

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