# `specs-hierarchy`
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Scene graph type hierarchy abstraction for use with [`specs`].
Builds up a `Hierarchy` resource, by querying a user supplied `Parent` component.
Requires the component to be `Tracked`.
Will send modification events on an internal `EventChannel`. Note that `Removed` events
does not mean the `Parent` component was removed from the component storage, just that the
`Entity` will no longer be considered to be a part of the `Hierarchy`. This is because the user
may wish to either remove only the component, the complete `Entity`, or something completely
different. When an `Entity` that is a parent gets removed from the hierarchy, the full tree of
children below it will also be removed from the hierarchy.
[`specs`]: https://github.com/slide-rs/specs
## Usage
```toml
# Cargo.toml
[dependencies]
specs-hierarchy = "0.5.1"
```
## Example
```rust
use specs::prelude::{Component, DenseVecStorage, Entity, FlaggedStorage};
use specs_hierarchy::{Hierarchy, Parent as HParent};
/// Component for defining a parent entity.
///
/// The entity with this component *has* a parent, rather than *is* a parent.
#[derive(Debug, Clone, Eq, Ord, PartialEq, PartialOrd)]
pub struct Parent {
/// The parent entity
pub entity: Entity,
}
impl Component for Parent {
type Storage = FlaggedStorage<Self, DenseVecStorage<Self>>;
}
impl HParent for Parent {
fn parent_entity(&self) -> Entity {
self.entity
}
}
```
## License
Licensed under either of
* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
* MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
at your option.
## Contribution
We are a community project that welcomes contribution from anyone. If you're interested in helping out, you can contact
us either through GitHub, or via [`gitter`](https://gitter.im/slide-rs/specs).
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any
additional terms or conditions.