# Bevy Easy Compute
[](https://docs.rs/bevy_app_compute)
[](https://crates.io/crates/bevy_app_compute)
An easy way to run wgpu compute shaders within a bevy app.
## Getting Started
Add the following line to your `Cargo.toml`
```toml
[dependencies]
bevy_app_compute = "0.16"
```
## Usage
### Setup
Declare your shaders in structs implementing `ComputeShader`. The `shader()` fn
should point to your shader source code. You need to derive `TypePath` as well:
```rust
#[derive(TypePath)]
struct SimpleShader;
impl ComputeShader for SimpleShader {
fn shader() -> ShaderRef {
"shaders/simple.wgsl".into()
}
}
```
Next, declare a struct implementing `ComputeWorker` to declare the bindings and
the logic of your worker:
```rust
#[derive(Resource)]
struct SimpleComputeWorker;
impl ComputeWorker for SimpleComputeWorker {
fn build(world: &mut World) -> AppComputeWorker<Self> {
let worker = AppComputeWorkerBuilder::new(world)
// Add a uniform variable
.add_uniform("uni", &5.)
// Add a staging buffer, it will be available from
// both CPU and GPU land.
.add_staging("values", &[1., 2., 3., 4.])
// Create a compute pass from your compute shader
// and define used variables
.add_pass::<SimpleShader>([4, 1, 1], &["uni", "values"])
.build();
worker
}
}
```
Don't forget to add a shader file to your `assets/` folder:
```rust
@group(0) @binding(0)
var<uniform> uni: f32;
@group(0) @binding(1)
var<storage, read_write> my_storage: array<f32>;
@compute @workgroup_size(1)
fn main(@builtin(global_invocation_id) invocation_id: vec3<u32>) {
my_storage[invocation_id.x] = my_storage[invocation_id.x] + uni;
}
```
Add the `AppComputePlugin` plugin to your app, as well as one
`AppComputeWorkerPlugin` per struct implementing `ComputeWorker`:
```rust
App::new()
// ... other plugins ...
.add_plugins(bevy_app_compute::AppComputeWorkerPlugin::<SimpleComputeWorker>::default());
```
Your compute worker will now run every frame, during the `PostUpdate` stage. To
read/write from it, use the `AppComputeWorker<T>` resource!
```rust
fn my_system(
mut compute_worker: ResMut<AppComputeWorker<SimpleComputeWorker>>
) {
if !compute_worker.ready() {
return;
};
let result: Vec<f32> = compute_worker.read_vec("values");
compute_worker.write_slice("values", [2., 3., 4., 5.]);
println!("got {:?}", result)
}
```
(see
[simple.rs](https://github.com/Kjolnyr/bevy_app_compute/tree/main/examples/simple.rs))
### Multiple passes
You can have multiple passes without having to copy data back to the CPU in
between:
```rust
let worker = AppComputeWorkerBuilder::new(world)
.add_uniform("value", &3.)
.add_storage("input", &[1., 2., 3., 4.])
.add_staging("output", &[0f32; 4])
// add each item + `value` from `input` to `output`
// the order of the values represents their binding order
.add_pass::<FirstPassShader>([4, 1, 1], &["value", "input", "output"])
// multiply each element of `output` by itself
.add_pass::<SecondPassShader>([4, 1, 1], &["output"])
.build();
// the `output` buffer will contain [16.0, 25.0, 36.0, 49.0]
```
(see
[multi_pass.rs](https://github.com/Kjolnyr/bevy_app_compute/tree/main/examples/multi_pass.rs))
### One shot computes
You can configure your worker to execute only when requested:
```rust
let worker = AppComputeWorkerBuilder::new(world)
.add_uniform("uni", &5.)
.add_staging("values", &[1., 2., 3., 4.])
.add_pass::<SimpleShader>([4, 1, 1], &["uni", "values"])
// This `one_shot()` function will configure your worker accordingly
.one_shot()
.build();
```
Then, you can call `execute()` on your worker when you are ready to execute it:
```rust
// Execute it only when the left mouse button is pressed.
fn on_click_compute(
buttons: Res<ButtonInput<MouseButton>>,
mut compute_worker: ResMut<AppComputeWorker<SimpleComputeWorker>>
) {
if !buttons.just_pressed(MouseButton::Left) { return; }
compute_worker.execute();
}
```
It will run at the end of the current frame, and you'll be able to read the data
in the next frame.
(see
[one_shot.rs](https://github.com/Kjolnyr/bevy_app_compute/tree/main/examples/one_shot.rs))
## Examples
See [examples](https://github.com/Kjolnyr/bevy_app_compute/tree/main/examples)
## Bevy version mapping
| 0.16 | 0.16 |