Painting foliage on mask

Hi guys,

I want to achieve the following:
Let’s say I have a black and white mask of a cobblestone texture (see example image).

What I want is to be able to paint grass (using the Paint Foliage tool) on a cobblestone material, but I would like the grass to only appear on the white parts of the mask.
I figured this effect is probably possible by using vertex painting, but I was wondering if I can also use a custom mask for this, since the result would probably more accurate.

How would I go about setting this up in a material?

Thanks :slight_smile: