Help with shader with uniform opacity when overlapped, globally mapped texture.

Hi Everyone,

I need a shader for various things in an RTS which does what the diagram on the right does. I know nothing about shaders, but am happy to learn.

That is, when I use a standard transparent shader, the opacity overlaps and combines as on the left, I want a uniform opacity, regardless of how many textured planes overlap.

Secondly, I need the shader to have a texture, which supports transparency, and is mapped by a coordinate system other than UV, like a global coordinate, so that when two planes overlap, the texture lines up as illustrated. If its important, this shader will primarily be used on the ground facing up.

If anyone can help by either pointing to tutorials, assets, or other resources I would be really grateful. Or if someone wants to take me through the code here, that's great as well.

I don't have any experience writing shaders, and with the new general shader, I'm not even sure if I should be extending that, or using a custom writing one from scratch.