NICE! That's awesome! I think everyone else (like me) just gives up. Just so I understand, are you using a composite map in the diffuse slot? And then using viewport canvas to target the blend mask of the top layer?
No actually there is no need for any composit material. It works with a standard material, because the magic is happening inside the viewport canvas layer editor. So you simple apply the very bottom texture to a standard material's diffuse slot, and then you choose this in the viewport canvas tool to paint on. then this…
Okay so here is a bit more detailed explanation about whats going on. It is not really possible to use multiple uv channels on the different layers with viewport canvas. In my example, we use a texture that is tiled with the uvs, so its uvmap looks like this: And it has a second uv channel, so that we can use with our…