Cat Stacker v2.0
My LD12 entry, Cat Stacker, has grown up and now features assorted fruit. Also, instead of the original tetrisy controls, you can click and drag the current piece around with no time pressure (press A and D to rotate). There are 20 levels and it get’s pretty tough. Good luck! (^ _ ^)/

The idea is that you do a dot product between the “expected/current” direction and the “new” one, which will be 1.0 as long as it’s moving in a straight line, but decrease as the path is curved. I guess using cross product would give similar results but with directionality for free, so you can just compare against zero to get direction and magnitude.