Functions and Lambdas
If you look at a basic OPENRNDR program and can’t stop thinking about that syntax with curly brackets following certain words, this section is for you.
Functions
Please read the section on functions in the Kotlin Tour all the way to the end. There you will learn about Lambda functions.
When you’re done, you should probably be able to understand the syntax of a basic OPENRNDR program: when we encounter code like extend { ... } we know that we are dealing with two functions. The first one is called extend() and the second one, { ... }, is an anonymous lambda function. In Kotlin, it’s not necessary to include the parentheses, as in extend({ ... }), if the last argument of the extend function is a Lambda function.
What extend { ... } does is calling the extend function to tell OPENRNDR: “here, take this anonymous function and execute it on every animation frame”.
Other creative coding frameworks usually expect one specific method, often called draw, where the user can draw to the screen.
Having an extend method that accepts a lambda function gives OPENRNDR the unique capability of combining multiple extend blocks in the same program.
The framework provides several such extend blocks (called Extensions), for instance, Screenshots, ScreenRecorder and Camera2D, among others. This makes it possible to build programs by composing code blocks as if they were LEGO pieces and add powerful functionality with just one or two lines of code.