# WGSL Preprocessor

This crate was created for my 3d game engine, Lyra Engine, which uses this as a preprocessor.

## Features

* Import constants, functions, and bindings from other modules
More to come, check out issues in this repo.

## How-To

### Preprocessing modules

To process modules, they first must be parsed to find the module paths of each file:

```rust
let mut p = Processor::new();

let inner_include_src = fs::read_to_string("shaders/inner_include.wgsl").unwrap();
let inner_module_path = p.parse_module(&inner_include_src)
    .unwrap().expect("failed to find module");

let simple_include_src = fs::read_to_string("shaders/simple.wgsl").unwrap();
let simple_module_path = p.parse_module(&simple_include_src)
    .unwrap().expect("failed to find module");

let base_include_src = fs::read_to_string("shaders/base.wgsl").unwrap();
let base_module_path = p.parse_module(&base_include_src)
    .unwrap().expect("failed to find module");
```

Then, after all the modules are parsed, you can preprocess the module. This is where all the imported modules and items are compiled into a single output shader:

```rust
let out = p.process_file(&base_module_path, &base_include_src).unwrap();
fs::write("out.wgsl", out).unwrap();
```

### Importing modules

To import modules, that module must have its path defined. Do to so, at the top of the file, use the preprocessor command `#define_module <module_path>` with `module_path` being the identifier of the module and how its imported:

```wgsl
/// ==== shadows.wgsl
#define_module engine::shadows

const PCF_SAMPLES_NUM: u32 = 32;

/// ==== pbr.wgsl
#define_module engine::pbr
#import engine::shadows::{PCF_SAMPLES_NUM}

fn fs_main(in: VertexOutput) -> vec4<f32> {
    // ...

    let samples_num = PCF_SAMPLES_NUM;

    // ...
}
```

The above example imports an item from the `engine::shadows` module. Keep in mind that you cannot have conflicted names of variables, functions, types, and other imported things. Instead of importing an item from the module, you can import the module and use items from it (still no conflicting names):

```wgsl
/// ==== shadows.wgsl
#define_module engine::shadows

const PCF_SAMPLES_NUM: u32 = 32;

/// ==== pbr.wgsl
#define_module engine::pbr
// not importing an item, but only a module
#import engine::shadows

fn fs_main(in: VertexOutput) -> vec4<f32> {
    // ...

    // use an item from the module here
    let samples_num = shadows::PCF_SAMPLES_NUM;

    // ...
}
```