I’ve been working on a small game recently, the goal of which is to change your player’s color to match the colors of incoming lines so that you can pass through them. Detecting when the player crosses a line is at the core of the game.
Detecting which side of a 2D line a point is on is a pretty simple task. I’d wager most people have encountered the problem relatively early in their game development efforts (not allowing the player to move outside of the screen, for example). Nonetheless it’s probably something that people (including me) have solved in an inefficient or needlessly complex way. So I’m going to go over the problem and solution implemented in my game.