Currently if you try to paint a texture that is world-Z aligned, it paints the texture as if it was using the mesh’s regular UVs (so if you paint somewhere on the mesh, the painting appears somewhere else in the world).
My use-case: I was going to use a single world-aligned texture mask to paint in my rain and puddles, dirt etc across a couple of city blocks, made from modular paths/road (vertex painting just requires a lot of tessellation to give the accuracy I’m after). But I guess there would be other applications for this too.
I’m not sure what the best way would be as far as UI goes - since there is a “Is default meshpaint texture” in a texture sample, maybe there could be a “Use This UV for texture painting” underneath it, so it knows how the texture is mapped. Or I guess in the UV dropdown where you select the UV channel, you could have a “WorldZ” option, and underneath a multiplier, which you could match up to the coords you are using (not as elegant).
For now I’ll just be hyper-tessellating and manually triangulating all the ground meshes + combining with a noise texture to try and make it look like it’s nicely painted.