Unity-like coroutines in plain old C

Let’s just begin with this: Coroutines are great!

For those who don’t know what coroutines are, let me explain:

Coroutines allow a function to be paused and resumed. This is often used to allow the concurrent execution of multiple functions (and is often what is used to implement async / await in most programming languages), but in Game Development, they are also used to spread a long running function over multiple frames.

In the above screencast, clicking on the button “DAMAGE” sets the red bar (representing health) to a specific value, and triggers a coroutine that changes the value of the orange bar progressively over time.

In this article, we’ll see how to implement this in C.

In-depth explanation of coroutines

Coroutine - Wikipedia

At its core, a coroutine can be modeled as a state machine: