Vray decal "texture" -- how does it work

[SonyBoy]

Can anyone explain how the decal mask texture works. Once again, docs are completely lacking any useful description of this VERY important feature of this tool. Docs state nothing more than:

"Mask – Masks the projected material based on a texture."

Really not helpful at all.

Since this is effectively a volumetric shader, and an image is 2D in nature, it's important to know how this works, which direction it is projected from and what controls (if any) there are to edit this. Is this a triplanar projection? Or what, exactly?

[fixeighted]

The mask is just a mask as in any other situation, where black is transparent and white opaque.
The decal is not a volumetric shader...just a projected texture with the mask used to cut away a portion of the texture, which is
what a decal in reality is

[SonyBoy]

It is volumetric in the sense that whatever is inside the decal widget (essentially a 3D cube) is affected by the shader attached to it, therefore it has 3D characteristics in world space. This includes directionality, however the widget has no indication which axis a 2D mask or image plugged into it will be applied from. Presumably it's projected, and projections always have directionality. It's very unclear.

[fixeighted]

The directionality is indicated by the arrow pointing out from the 'top' of the widget.
I realise that Maya's version of this looks a little different to Max's but it's still there, as in this video https://www.youtube.com/watch?v=2WAS4zgIerI&t=36s

[SonyBoy]

I see now that there is an arrow, although it's not particularly noticeable especially when the widget is non uniformly scaled. However, after some personal testing I can see now that it's possible to at least use a triplanar node plugged into the mask slot to get a more useful volumetric effect with a 2D texture. But this is again another example of Chaos documentation just being thoroughly lazy and inadequate, which seems to be a recurring issue. This is a new and unusual tool and warranted some better explanation and examples given for the mask attribute. Just describing what is patently obvious (hey, the mask slot is where you plug in a mask!) is NOT documentation.

[fixeighted]

I think Maya's version must work differently to that of Max, as in Max that is simply not possible, as it is just a 2d decal.
Honestly I can't imagine how a triplanar node as a mask would work volumetrically, though I'd like to see your result.

I'll leave it to other Maya users to explore further in any case

[SonyBoy]

The behavior you're describing sounds more like a regular 2D projection, which has been around forever. There wouldn't be much point to the decal if that's all it did.

[SonyBoy]

Simple proof of concept test -- red areas are the mask on a decal, a simple checker texture run through a triplanar node.