# Objective
Currently, `DynamicScene`s extract all components listed in the given
(or the world's) type registry. This acts as a quasi-filter of sorts.
However, it can be troublesome to use effectively and lacks decent
control.
For example, say you need to serialize only the following component over
the network:
```rust
#[derive(Reflect, Component, Default)]
#[reflect(Component)]
struct NPC {
name: Option<String>
}
```
To do this, you'd need to:
1. Create a new `AppTypeRegistry`
2. Register `NPC`
3. Register `Option<String>`
If we skip Step 3, then the entire scene might fail to serialize as
`Option<String>` requires registration.
Not only is this annoying and easy to forget, but it can leave users
with an impossible task: serializing a third-party type that contains
private types.
Generally, the third-party crate will register their private types
within a plugin so the user doesn't need to do it themselves. However,
this means we are now unable to serialize _just_ that type— we're forced
to allow everything!
## Solution
Add the `SceneFilter` enum for filtering components to extract.
This filter can be used to optionally allow or deny entire sets of
components/resources. With the `DynamicSceneBuilder`, users have more
control over how their `DynamicScene`s are built.
To only serialize a subset of components, use the `allow` method:
```rust
let scene = builder
.allow::<ComponentA>()
.allow::<ComponentB>()
.extract_entity(entity)
.build();
```
To serialize everything _but_ a subset of components, use the `deny`
method:
```rust
let scene = builder
.deny::<ComponentA>()
.deny::<ComponentB>()
.extract_entity(entity)
.build();
```
Or create a custom filter:
```rust
let components = HashSet::from([type_id]);
let filter = SceneFilter::Allowlist(components);
// let filter = SceneFilter::Denylist(components);
let scene = builder
.with_filter(Some(filter))
.extract_entity(entity)
.build();
```
Similar operations exist for resources:
<details>
<summary>View Resource Methods</summary>
To only serialize a subset of resources, use the `allow_resource`
method:
```rust
let scene = builder
.allow_resource::<ResourceA>()
.extract_resources()
.build();
```
To serialize everything _but_ a subset of resources, use the
`deny_resource` method:
```rust
let scene = builder
.deny_resource::<ResourceA>()
.extract_resources()
.build();
```
Or create a custom filter:
```rust
let resources = HashSet::from([type_id]);
let filter = SceneFilter::Allowlist(resources);
// let filter = SceneFilter::Denylist(resources);
let scene = builder
.with_resource_filter(Some(filter))
.extract_resources()
.build();
```
</details>
### Open Questions
- [x] ~~`allow` and `deny` are mutually exclusive. Currently, they
overwrite each other. Should this instead be a panic?~~ Took @soqb's
suggestion and made it so that the opposing method simply removes that
type from the list.
- [x] ~~`DynamicSceneBuilder` extracts entity data as soon as
`extract_entity`/`extract_entities` is called. Should this behavior
instead be moved to the `build` method to prevent ordering mixups (e.g.
`.allow::<Foo>().extract_entity(entity)` vs
`.extract_entity(entity).allow::<Foo>()`)? The tradeoff would be
iterating over the given entities twice: once at extraction and again at
build.~~ Based on the feedback from @Testare it sounds like it might be
better to just keep the current functionality (if anything we can open a
separate PR that adds deferred methods for extraction, so the
choice/performance hit is up to the user).
- [ ] An alternative might be to remove the filter from
`DynamicSceneBuilder` and have it as a separate parameter to the
extraction methods (either in the existing ones or as added
`extract_entity_with_filter`-type methods). Is this preferable?
- [x] ~~Should we include constructors that include common types to
allow/deny? For example, a `SceneFilter::standard_allowlist` that
includes things like `Parent` and `Children`?~~ Consensus suggests we
should. I may split this out into a followup PR, though.
- [x] ~~Should we add the ability to remove types from the filter
regardless of whether an allowlist or denylist (e.g.
`filter.remove::<Foo>()`)?~~ See the first list item
- [x] ~~Should `SceneFilter` be an enum? Would it make more sense as a
struct that contains an `is_denylist` boolean?~~ With the added
`SceneFilter::None` state (replacing the need to wrap in an `Option` or
rely on an empty `Denylist`), it seems an enum is better suited now
- [x] ~~Bikeshed: Do we like the naming convention? Should we instead
use `include`/`exclude` terminology?~~ Sounds like we're sticking with
`allow`/`deny`!
- [x] ~~Does this feature need a new example? Do we simply include it in
the existing one (maybe even as a comment?)? Should this be done in a
followup PR instead?~~ Example will be added in a followup PR
### Followup Tasks
- [ ] Add a dedicated `SceneFilter` example
- [ ] Possibly add default types to the filter (e.g. deny things like
`ComputedVisibility`, allow `Parent`, etc)
---
## Changelog
- Added the `SceneFilter` enum for filtering components and resources
when building a `DynamicScene`
- Added methods:
- `DynamicSceneBuilder::with_filter`
- `DynamicSceneBuilder::allow`
- `DynamicSceneBuilder::deny`
- `DynamicSceneBuilder::allow_all`
- `DynamicSceneBuilder::deny_all`
- `DynamicSceneBuilder::with_resource_filter`
- `DynamicSceneBuilder::allow_resource`
- `DynamicSceneBuilder::deny_resource`
- `DynamicSceneBuilder::allow_all_resources`
- `DynamicSceneBuilder::deny_all_resources`
- Removed methods:
- `DynamicSceneBuilder::from_world_with_type_registry`
- `DynamicScene::from_scene` and `DynamicScene::from_world` no longer
require an `AppTypeRegistry` reference
## Migration Guide
- `DynamicScene::from_scene` and `DynamicScene::from_world` no longer
require an `AppTypeRegistry` reference:
```rust
// OLD
let registry = world.resource::<AppTypeRegistry>();
let dynamic_scene = DynamicScene::from_world(&world, registry);
// let dynamic_scene = DynamicScene::from_scene(&scene, registry);
// NEW
let dynamic_scene = DynamicScene::from_world(&world);
// let dynamic_scene = DynamicScene::from_scene(&scene);
```
- Removed `DynamicSceneBuilder::from_world_with_type_registry`. Now the
registry is automatically taken from the given world:
```rust
// OLD
let registry = world.resource::<AppTypeRegistry>();
let builder = DynamicSceneBuilder::from_world_with_type_registry(&world,
registry);
// NEW
let builder = DynamicSceneBuilder::from_world(&world);
```
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