In this section, we will program a small physics sandbox. We're not going very in-depth, as this is intended to be a small introduction to the physics engine, not a complete tutorial. Let's first explain some information that you'll need to know when you're using GameMaker's physics engine. For one, you should not mix physics-specific code with code that controls movement that doesn't use physics (for example, use physics speed variables rather than the variable speed). It's also important to limit how many physics instances are active at once in your game, as they use intense calculations to make everything flow properly. In relation to this, use parenting for collision checks—children will not inherit physics properties, but they can inherit collision events. If you had five different enemies, it's best to have your player check for a collision with a parent rather than all five of those different enemies, if you can.

But anyway, let's start with making our physics game....