At first I drew a semi-circle and used the line of sight to do this. Problem is, the semi-circle sprite goes through platforms where the enemies clearly can't see.
Currently, I'm looking at placing boxes all throughout the game and saying if they're within a certain range of an enemy they will be visible with say 30% opacity. Having troubles with getting them to do this. It also seems quite demanding to do this.
Does anyone have a more elegant solution?