Writing Custom Shaders

Walkthrough

Use WebGPU Shader Language (WGSL) to add visual effects to your game.

Create a `shaders` folder

Inside your project directory, create a folder named shaders. This folder will contain all your game shaders.

your-project-dir/       # Your project's root directory.
├── shaders/            # The directory of your shaders. 
├── src/                # The directory of your code.
│   └── lib.rs          # The main file for the game.
├── Cargo.toml          # Rust project manifest.
└── turbo.toml          # Turbo configuration.

Add a shader

Let's add a shader called my-awesome-shader.wgsl to the shaders directory. Here's some boilerplate you can use as a starting point:

shaders/my-awesome-shader.wgsl

// Global uniform with viewport and tick fields
struct Global {
    camera: vec3<f32>,
    tick: u32,
    viewport: vec2<f32>,
}
 
@group(0) @binding(0)
var<uniform> global: Global;
 
// Vertex input to the shader
struct VertexInput {
    @location(0) pos: vec2<f32>,
    @location(1) uv: vec2<f32>,
};
 
// Output color fragment from the shader
struct VertexOutput {
    @builtin(position) position: vec4<f32>,
    @location(1) uv: vec2<f32>,
};
 
// Main vertex shader function
@vertex
fn vs_main(in: VertexInput) -> VertexOutput {
    var out: VertexOutput;
    out.position = vec4<f32>(in.pos, 0., 1.);
    out.uv = in.uv;
    return out;
}
 
// Bindings for the texture
@group(1) @binding(0)
var t_canvas: texture_2d<f32>;
 
// Sampler for the texture
@group(1) @binding(1)
var s_canvas: sampler;
 
// Main fragment shader function
@fragment
fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
    var color: vec4<f32> = textureSample(t_canvas, s_canvas, in.uv);
    return color;
}

Modify the shader

So far, our shader isn't doing anything custom. So let's make the cycle the intensity of red, green, and blue color channels over time. At the bottom of the shader file add the applyColorCycle function and use it in the fs_main fragment shader entrypoint to modify the existing color variable:

shaders/my-awesome-shader.wgsl

@fragment
fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
    var color: vec4<f32> = textureSample(t_canvas, s_canvas, in.uv);
    color = applyColorCycle(color, uv, global.tick);
    return color;
}
 
fn applyColorCycle(color: vec4<f32>, uv: vec2<f32>, tick: u32) -> vec4<f32> {
    let time: f32 = f32(tick) * 0.1;
    let r: f32 = 0.5 + 0.5 * sin(time + uv.x);
    let g: f32 = 0.5 + 0.5 * sin(time + uv.y + 2.0);
    let b: f32 = 0.5 + 0.5 * sin(time + uv.x + 4.0);
    return mix(vec4<f32>(r, g, b, color.a), color, 0.8);
}

Use the shader

There are two ways to use the shader in your game. Depending on your use-case, you may even wish to use both approaches. They are not mutually-exclusive.

Option A - Set it in the config

If you plan to use a single custom shader 100% of the time, this should have you covered. Add or modify the shader section of your Turbo config by setting a default-surface-shader:

turbo.toml

[shader]
default-surface-shader = "my-awesome-shader"

Option B - Activate it at runtime

You can dynamically swap shaders while your game is running.

`shaders::set`

Activate a custom shader:

shaders::set("my-awesome-shader");

`shaders::reset`

Deactivate any active custom shaders:

shaders::reset();

`shaders::get`

Get the name of the currently active custom shader:

let shader_name = shaders::get();