# Objective
- Adds the ability for picking backends to add custom hit data
- Fixes#16186
## Solution
- Adds an `extra` field to the HitData struct which can take any Data
that implements HitDataExtra. This is stored in an Arc which can be
downcast with a helper function in the system that consumes the hit.
- In the original ticket I suggested using a generic, however this
caused extensive code changes and complications down the line with the
HoverMap and OverMap so I decided against it.
## Testing
- I added an example custom_hit_data to test the new feature
- I tested all other picking examples to ensure they still work as
expected
- I tested the examples on Ubuntu
- I additionally tested the custom_hit_data example in wasm
---
## Showcase
<details>
<summary>Click to view showcase</summary>
### Creating custom hits:
```rust
let picks: Vec<(Entity, HitData)> = ray_cast
.cast_ray(ray, &settings)
.iter()
.map(|(entity, hit)| {
let extra = TriangleHitInfo {
triangle_vertices: hit.triangle,
};
let hit_data = HitData::new_with_extra(
ray_id.camera,
hit.distance,
Some(hit.point),
Some(hit.normal),
extra,
);
(*entity, hit_data)
})
.collect();
```
### Reading custom hits:
```rust
for hits in pointer_hits.read() {
for (_, hit) in &hits.picks {
let Some(info) = hit.extra_as::<TriangleHitInfo>() else {
continue;
};
let Some(vertices) = info.triangle_vertices else {
continue;
};
// do something cool with your custom hit data
}
}
```
### An example of what you can do with this
<img width="1291" height="730" alt="image"
src="https://github.com/user-attachments/assets/2d0e8aed-7059-470a-a0f6-1453356cfe6a"
/>
</details>
Martin Edlund