Decal layering with alpha respected

[SonyBoy]

Doing some testing with a decal as a way to layer mud over an entire scene and running into this issue. If the decal is layered over geometry that it set as a matte object with black hole alpha, the alpha is not respected. I have the decal layered on top of my LIDAR geo, which has an object properties node applied and is set to be a matte object with black hole alpha.

Without the decal, this renders correctly with nothing in RGB and a black hole alpha contribution. As soon as the decal is applied, the matte properties are ignored and I get unwanted values in both RGB and alpha even where the mask on the decal dictates there should be nothing.

Not sure if I'm pushing the intended use of the decal beyond what it's capable of, but from a purely technical perspective this doesn't make sense. Is there some way to achieve what I'm trying to do using the decal?

Also, as I've complained about previously the decal docs are lacking. And, why does the decal have built-in dimension attributed (Width, Height, Depth) when it can be scaled interactively to achieve what appear to be the same results?

[vladimir_krastev]

Hi, thanks for posting. I tested this in 3ds Max and Maya. In 3ds Max as soon as we have a decal over a matte surface, it's Alpha gets to -1 and disappears from RGB

In Maya adding a naked VRayDecal does as you said, stays in RGB and Alpha.
If we add the matte properties to the VRayDecal as well it acts correctly in RGB but still renders in Alpha.
So far this seems like a bug. Let me check it a bit more carefully and I will get back to the thread.

[SonyBoy]

So far as I can tell, this must be a bug and it seems texture specific. If I use a checker texture as the mask without assigning the decal as a matte object, it behaves correctly, i.e. I get nothing in RGB where there are zero values and the alpha is black hole for the necessary compositing result. If I plug in a noise texture to the exact same setup, I get a very confusing result -- the decal shader is red but there are white areas now in the RGB (no idea where this is coming from), and the alpha renders solid inside the entire decal volume.

[vladimir_krastev]

Hi, there is an issue with the Alpha contribution and Decal. If you add a mask this affects the Alpha of the Decal but still it should not appear without a mask as it does. I logged it under VMAYA-12098 in our bug tracking system.

[SonyBoy]

Thanks, this is a disappointing limitation then. Hopefully this can be addressed quickly.

[Twist]

Was going to make a new thread about this but found this one.

Any news on this yet? If it's not fixed decals are pretty much useless if stacked.

[vladimir_krastev]

Hi, thanks for posting. The issue is not fixed yet. I will add your post to the list of client requests to raise the priority. We will notify you when we have progress.

[Twist]

Hi, thanks for posting. The issue is not fixed yet. I will add your post to the list of client requests to raise the priority. We will notify you when we have progress.

Thank you!