Ok, I think I've sussed what I need to do to get basic touchscreen controls working.

I need an interface where: if player swipes left to right, player character moves from left to right. The same occurs for all 4 directions.

The expression DragAlpha seems, from what I understand, to calculate the difference between the finger touch's starting X/Y position and the end X/Y position. I assume, from that, the mechanic will work.

But the expression won't seem to accept, I get a syntax error saying about touch number or something?

I've tried changing from 0 to 1, 2 etc. but nothing. I don't get it? What is 0 Based?