Martin Edlund c3c118c20c Add support for custom picking data (#23245) ...

# 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>

2026-04-23 16:18:18 +00:00

..

custom_hit_data.rs

Add support for custom picking data (#23245)

2026-04-23 16:18:18 +00:00

debug_picking.rs

Contact Shadows (#22382)

2026-01-13 21:51:39 +00:00

dragdrop_picking.rs

Use the shorthand functions to construct Vals and UiRects in examples (#22765)

2026-02-02 23:27:19 +00:00

mesh_picking.rs

Contact Shadows (#22382)

2026-01-13 21:51:39 +00:00

simple_picking.rs

Contact Shadows (#22382)

2026-01-13 21:51:39 +00:00

sprite_picking.rs

Event Rearchitecture (#20731)

2025-09-09 23:48:55 +00:00