Handmade Hero gives good advice how to modularize to make a game portable. For many things you want to achieve, you can have the platform call the game instead

Handmade Hero gives good advice how to modularize to make a game portable. For many things you want to achieve, you can have the platform call the game instead of the other way around. Essentially it's (asynchronous) event driven architecture which enforces modularization. Think of a system as shipping data packets around, then it should be much easier to see how to swap out the platform parts.