# Objective
- Fixes#7352
## Solution
GLES doesn't support binding specific mip levels for sampling. Fallback
to using separate textures instead.
-
[wgpu-hal/src/gles/device.rs](628a95cd1c/wgpu-hal/src/gles/device.rs (L1038))
---
---------
Co-authored-by: Wilhelm Vallrand <>
# Objective
This method has no documentation and it's extremely unclear what it
does, or what the returned tick represents.
## Solution
Write documentation.
# Objective
- Improve speed of loading examples on the website
- Triggered by https://news.ycombinator.com/item?id=35996393
## Solution
- Use wasm-opt to optimize files for size. This reduces the files from
22mb to 13mb
- Cloudflare doesn't set the correct `Content-Type` header by default
for wasm files, add it manually. This enables wasm streaming and
compression, dropping the transfer to 3.9mb
The files with this script are deployed on
optimized.wasm-pages.pages.dev if you want to test, you can replace this
URL on a website deployed locally.
# Objective
- Update dependencies `ruzstd` and `basis-universal`
- Alternative to #5278 and #8133
## Solution
- Update the dependencies, fix the code
- Bevy now also depend on `syn@2` so it's not a blocker to update
`ruzstd` anymore
# Objective
Fix an out-of-date doc string.
The old doc string says "returns None if …" and "for a given
descriptor",
but this method neither takes an argument or returns an `Option`.
# Objective
Add support for the [Netpbm](https://en.wikipedia.org/wiki/Netpbm) image
formats, behind a `pnm` feature flag.
My personal use case for this was robotics applications, with `pgm`
being a popular format used in the field to represent world maps in
robots.
I chose the formats and feature name by checking the logic in
[image.rs](a35ed552fa/crates/bevy_render/src/texture/image.rs (L76))
## Solution
Quite straightforward, the `pnm` feature flag already exists in the
`image` crate so it's just creating and exposing a `pnm` feature flag in
the root `Cargo.toml` and forwarding it through `bevy_internal` and
`bevy_render` all the way to the `image` crate.
---
## Changelog
### Added
`pnm` feature to add support for `pam`, `pbm`, `pgm` and `ppm` image
formats.
---------
Signed-off-by: Luca Della Vedova <lucadv@intrinsic.ai>
# Objective
Bevy code tends to make heavy use of the [newtype](
https://doc.rust-lang.org/rust-by-example/generics/new_types.html)
pattern, which is why we have a dedicated derive for
[`Deref`](https://doc.rust-lang.org/std/ops/trait.Deref.html) and
[`DerefMut`](https://doc.rust-lang.org/std/ops/trait.DerefMut.html).
This derive works for any struct with a single field:
```rust
#[derive(Component, Deref, DerefMut)]
struct MyNewtype(usize);
```
One reason for the single-field limitation is to prevent confusion and
footguns related that would arise from allowing multi-field structs:
<table align="center">
<tr>
<th colspan="2">
Similar structs, different derefs
</th>
</tr>
<tr>
<td>
```rust
#[derive(Deref, DerefMut)]
struct MyStruct {
foo: usize, // <- Derefs usize
bar: String,
}
```
</td>
<td>
```rust
#[derive(Deref, DerefMut)]
struct MyStruct {
bar: String, // <- Derefs String
foo: usize,
}
```
</td>
</tr>
<tr>
<th colspan="2">
Why `.1`?
</th>
</tr>
<tr>
<td colspan="2">
```rust
#[derive(Deref, DerefMut)]
struct MyStruct(Vec<usize>, Vec<f32>);
let mut foo = MyStruct(vec![123], vec![1.23]);
// Why can we skip the `.0` here?
foo.push(456);
// But not here?
foo.1.push(4.56);
```
</td>
</tr>
</table>
However, there are certainly cases where it's useful to allow for
structs with multiple fields. Such as for structs with one "real" field
and one `PhantomData` to allow for generics:
```rust
#[derive(Deref, DerefMut)]
struct MyStruct<T>(
// We want use this field for the `Deref`/`DerefMut` impls
String,
// But we need this field so that we can make this struct generic
PhantomData<T>
);
// ERROR: Deref can only be derived for structs with a single field
// ERROR: DerefMut can only be derived for structs with a single field
```
Additionally, the possible confusion and footguns are mainly an issue
for newer Rust/Bevy users. Those familiar with `Deref` and `DerefMut`
understand what adding the derive really means and can anticipate its
behavior.
## Solution
Allow users to opt into multi-field `Deref`/`DerefMut` derives using a
`#[deref]` attribute:
```rust
#[derive(Deref, DerefMut)]
struct MyStruct<T>(
// Use this field for the `Deref`/`DerefMut` impls
#[deref] String,
// We can freely include any other field without a compile error
PhantomData<T>
);
```
This prevents the footgun pointed out in the first issue described in
the previous section, but it still leaves the possible confusion
surrounding `.0`-vs-`.#`. However, the idea is that by making this
behavior explicit with an attribute, users will be more aware of it and
can adapt appropriately.
---
## Changelog
- Added `#[deref]` attribute to `Deref` and `DerefMut` derives
# Objective
The unit test `chang_tick_wraparound` is meant to ensure that change
ticks correctly deal with wrapping by setting the world's
`last_change_tick` to `u32::MAX`. However, since systems don't use* the
value of `World::last_change_tick`, this test doesn't actually involve
any wrapping behavior.
*exclusive systems do use `World::last_change_tick`; however it gets
overwritten by the system's own last tick in `System::run`.
## Solution
Use `QueryState` instead of systems in the unit test. This approach
actually uses `World::last_change_tick`, so it properly tests that
change ticks deal with wrapping correctly.
# Objective
- Simplify API and make authoring styles easier
See:
https://github.com/bevyengine/bevy/issues/8540#issuecomment-1536177102
## Solution
- The `size`, `min_size`, `max_size`, and `gap` properties have been
replaced by `width`, `height`, `min_width`, `min_height`, `max_width`,
`max_height`, `row_gap`, and `column_gap` properties
---
## Changelog
- Flattened `Style` properties that have a `Size` value directly into
`Style`
## Migration Guide
- The `size`, `min_size`, `max_size`, and `gap` properties have been
replaced by the `width`, `height`, `min_width`, `min_height`,
`max_width`, `max_height`, `row_gap`, and `column_gap` properties. Use
the new properties instead.
---------
Co-authored-by: ickshonpe <david.curthoys@googlemail.com>
# Objective
- Fix#5631
## Solution
- Wait 50ms (configurable) after the last modification event before
reloading an asset.
---
## Changelog
- `AssetPlugin::watch_for_changes` is now a `ChangeWatcher` instead of a
`bool`
- Fixed https://github.com/bevyengine/bevy/issues/5631
## Migration Guide
- Replace `AssetPlugin::watch_for_changes: true` with e.g.
`ChangeWatcher::with_delay(Duration::from_millis(200))`
---------
Co-authored-by: François <mockersf@gmail.com>
# Objective
- Fix bad links in the WebGPU example page
## Solution
- Bevy website always add the trailing slash, keep the link relative by
removing the current folder from it
# Objective
- Cleanup file tree
## Solution
A mysterious mod.rs lies in the scene_viewer directory. It seems
completely useless, everything ignores it and it doesn't affect
anything.
We cruelly remove it, making the world a less whimsical place. A
dystopian drive for pure and complete order compels us to eliminate all
that is useless, for clarity and to prevent the wonder and beauty of
confusion.
# Objective
* `Node::physical_rect` divides the logical size of the node by the
scale factor, when it should multiply.
* Add a `physical_size` method to `Node` that calculates the physical
size of a node.
---
## Changelog
* Added a method `physical_size` to `Node` that calculates the physical
size of the `Node` based on the given scale factor.
* Fixed the `Node::physical_rect` method, the logical size should be
multiplied by the scale factor to get the physical size.
* Removed the `scale_value` function from the `text` widget module and
replaced its usage with `Node::physical_size`.
* Derived `Copy` for `Node` (since it's only a wrapped `Vec2`).
* Made `Node::size` const.
# Objective
`ScheduleGraph` currently stores run conditions in a
`Option<Vec<BoxedCondition>>`. The `Option` is unnecessary, since we can
just use an empty vector instead of `None`.
# Objective
The method `UnsafeWorldCell::world_mut` is a special case, since its
safety contract is more difficult to satisfy than the other methods on
`UnsafeWorldCell`. Rewrite its documentation to be specific about when
it can and cannot be used. Provide examples and emphasize that it is
unsound to call in most cases.
# Objective
The method `UnsafeWorldCell::read_change_tick` is longer than it needs
to be. `World` only has a method called this because it has two methods
for getting a change tick: one that takes `&self` and one that takes
`&mut self`. Since this distinction is not applicable to
`UnsafeWorldCell`, we should just call this method `change_tick`.
## Solution
Deprecate the current method and add a new one called `change_tick`.
---
## Changelog
- Renamed `UnsafeWorldCell::read_change_tick` to `change_tick`.
## Migration Guide
The `UnsafeWorldCell` method `read_change_tick` has been renamed to
`change_tick`.
# Objective
`ScheduleRunnerPlugin` was still configured via a resource, meaning
users would be able to change the settings while the app is running, but
the changes wouldn't have an effect.
## Solution
Configure plugin directly
---
## Changelog
- Changed: merged `ScheduleRunnerSettings` into `ScheduleRunnerPlugin`
## Migration Guide
- instead of inserting the `ScheduleRunnerSettings` resource, configure
the `ScheduleRunnerPlugin`
# Objective
- Fixes#3531
## Solution
- Added an append wrapper to BufferVec based on the function signature
for vec.append()
---
First PR to Bevy. I didn't see any tests for other BufferVec methods
(could have missed them) and currently this method is not used anywhere
in the project. Let me know if there are tests to add or if I should
find somewhere to use append so it is not dead code. The issue mentions
implementing `truncate` and `extend` which were already implemented and
merged
[here](https://github.com/bevyengine/bevy/pull/6833/files#diff-c8fb332382379e383f1811e30c31991b1e0feb38ca436c357971755368012ced)
# Objective
Frustum culling for 2D components has been enabled since #7885,
Fixes#8490
## Solution
Re-introduced the comments about frustum culling in the
many_animated_sprites.rs and many_sprites.rs examples.
---------
Co-authored-by: Nicola Papale <nicopap@users.noreply.github.com>
Co-authored-by: François <mockersf@gmail.com>
# Objective
Replace `Query<&T, Changed<T>>` style queries with the more efficient
`Query<Ref<T>>` form in two of the UI systems.
---
## Changelog
Replaced use of `Changed` with `Ref` in queries in the
`ui_layout_system` and `calc_bounds` UI systems.
# Objective
- When writing render nodes that need a view, you always need to define
a `Query` on the associated view and make sure to update it manually and
query it manually. This is verbose and error prone.
## Solution
- Introduce a new `ViewNode` trait and `ViewNodeRunner` `Node` that will
take care of managing the associated view query automatically.
- The trait is currently a passthrough of the `Node` trait. So it still
has the update/run with all the same data passed in.
- The `ViewNodeRunner` is the actual node that is added to the render
graph and it contains the custom node. This is necessary because it's
the one that takes care of updating the node.
---
## Changelog
- Add `ViewNode`
- Add `ViewNodeRunner`
## Notes
Currently, this only handles the view query, but it could probably have
a ReadOnlySystemState that would also simplify querying all the readonly
resources that most render nodes currently query manually. The issue is
that I don't know how to do that without a `&mut self`.
At first, I tried making this a default feature of all `Node`, but I
kept hitting errors related to traits and generics and stuff I'm not
super comfortable with. This implementations is much simpler and keeps
the default Node behaviour so isn't a breaking change
## Reviewer Notes
The PR looks quite big, but the core of the PR is the changes in
`render_graph/node.rs`. Every other change is simply updating existing
nodes to use this new feature.
## Open questions
~~- Naming is not final, I'm opened to anything. I named it
ViewQueryNode because it's a node with a managed Query on a View.~~
~~- What to do when the query fails? All nodes using this pattern
currently just `return Ok(())` when it fails, so I chose that, but
should it be more flexible?~~
~~- Is the ViewQueryFilter actually necessary? All view queries run on
the entity that is already guaranteed to be a view. Filtering won't do
much, but maybe someone wants to control an effect with the presence of
a component instead of a flag.~~
~~- What to do with Nodes that are empty struct? Implementing
`FromWorld` is pretty verbose but not implementing it means there's 2
ways to create a `ViewNodeRunner` which seems less ideal. This is an
issue now because most node simply existed to hold the query, but now
that they don't hold the query state we are left with a bunch of empty
structs.~~
- Should we have a `RenderGraphApp::add_render_graph_view_node()`, this
isn't necessary, but it could make the code a bit shorter.
---------
Co-authored-by: Carter Anderson <mcanders1@gmail.com>
# Objective
- Add Reflect and FromReflect for AssetPath
- Fixes#8458
## Solution
- Straightforward derive of `Reflect` and `FromReflect` for `AssetPath`
- Implement `Reflect` and `FromReflect` for `Cow<'static, Path>` as to
satisfy the 'static lifetime requierments of bevy_reflect.
Implementation is a direct copy of that for `Cow<'static, str>` so maybe
it begs the question that was already asked in #7429 - maybe it would be
benefitial to write a general implementation for `Reflect` for
`Cow<'static, T>`.
# Objective
- Replace the `example_showcase.sh` script
- Helper tool to prepare the example page on the website
## Solution
- Have a command to run all the examples: `cargo run -p example-showcase
-- run`
- Have a command to take screenshots of all examples: `cargo run -p
example-showcase -- run --screenshot`
- Have a command to build the markdown files for the website: `cargo run
-p example-showcase -- build-website-list --content-folder content`
- Have a command to build all the examples in wasm/WebGPU: `cargo run -p
example-showcase -- build-web-gpu-examples --content-folder webgpus`
(with `--website-hacks` to enable the hacks for the Bevy website: canvas
id, resizing and loading bar)
This is the first step to an improved example page (all examples marked
as wasm, uses the card layout, has screenshots, reuse name, category and
description from the metadata). As one of the goal is to have a page
with WebGPU examples before the official release, this is not touching
the example page for now but targeting a new one.
<img width="1912" alt="Screenshot 2023-05-06 at 17 16 25"
src="https://user-images.githubusercontent.com/8672791/236632744-4372c95f-c50a-4168-973f-349412548f33.png">
# Objective
Sometimes we might want to read from the depth texture in some custom
rendering features. We must then add `STORAGE_BINDING` or
`TEXTURE_BINDING` to the texture usage flags when creating them.
## Solution
This PR allows one to customize the usage flags in the `Camera3d`
component.
# Objective
- Fixes#8563
## Solution
~~- Implement From<Color> for [u8; 4]~~
~~- also implement From<[u8; 4]> for Color because why not.~~
- implement method `as_rgba_u8` in Color
---------
Co-authored-by: Gino Valente <49806985+MrGVSV@users.noreply.github.com>
# Objective
`text_system` and `measure_text_system` both keep local queues to keep
track of text node entities that need recomputations/remeasurement,
which scales very badly with large numbers of text entities (O(n^2)) and
makes the code quite difficult to understand.
Also `text_system` filters for `Changed<Text>`, this isn't something
that it should do. When a text node entity fails to be processed by
`measure_text_system` because a font can't be found, the text node will
still be added to `text_system`'s local queue for recomputation. `Text`
should only ever be queued by `text_system` when a text node's geometry
is modified or a new measure is added.
## Solution
Remove the local text queues and use a component `TextFlags` to schedule
remeasurements and recomputations.
## Changelog
* Created a component `TextFlags` with fields `remeasure` and
`recompute`, which can be used to schedule a text `remeasure` or
`recomputation` respectively and added it to `TextBundle`.
* Removed the local text queues from `measure_text_system` and
`text_system` and instead use the `TextFlags` component to schedule
remeasurements and recomputations.
## Migration Guide
The component `TextFlags` has been added to `TextBundle`.
# Objective
Copy the `debug::print_tree` function from Taffy except display entity
ids instead of Taffy's node ids and indicate which ui nodes have a
measure func.
# Objective
Ensure future consistency between the two compare functions for all
types with manual `Ord` and `PartialOrd` implementations.
## Solution
Use `Self::cpm` in the implementation of `partial_cpm` for types
`Handle` and `Name`.
# Objective
there were typos in AxisSettings livezone/deadzone get/set function doc
comments.
## Solution
I changed the comments to be (hopefully) correct this time. I could be
wrong though.
# Objective
- Support WebGPU
- alternative to #5027 that doesn't need any async / await
- fixes#8315
- Surprise fix#7318
## Solution
### For async renderer initialisation
- Update the plugin lifecycle:
- app builds the plugin
- calls `plugin.build`
- registers the plugin
- app starts the event loop
- event loop waits for `ready` of all registered plugins in the same
order
- returns `true` by default
- then call all `finish` then all `cleanup` in the same order as
registered
- then execute the schedule
In the case of the renderer, to avoid anything async:
- building the renderer plugin creates a detached task that will send
back the initialised renderer through a mutex in a resource
- `ready` will wait for the renderer to be present in the resource
- `finish` will take that renderer and place it in the expected
resources by other plugins
- other plugins (that expect the renderer to be available) `finish` are
called and they are able to set up their pipelines
- `cleanup` is called, only custom one is still for pipeline rendering
### For WebGPU support
- update the `build-wasm-example` script to support passing `--api
webgpu` that will build the example with WebGPU support
- feature for webgl2 was always enabled when building for wasm. it's now
in the default feature list and enabled on all platforms, so check for
this feature must also check that the target_arch is `wasm32`
---
## Migration Guide
- `Plugin::setup` has been renamed `Plugin::cleanup`
- `Plugin::finish` has been added, and plugins adding pipelines should
do it in this function instead of `Plugin::build`
```rust
// Before
impl Plugin for MyPlugin {
fn build(&self, app: &mut App) {
app.insert_resource::<MyResource>
.add_systems(Update, my_system);
let render_app = match app.get_sub_app_mut(RenderApp) {
Ok(render_app) => render_app,
Err(_) => return,
};
render_app
.init_resource::<RenderResourceNeedingDevice>()
.init_resource::<OtherRenderResource>();
}
}
// After
impl Plugin for MyPlugin {
fn build(&self, app: &mut App) {
app.insert_resource::<MyResource>
.add_systems(Update, my_system);
let render_app = match app.get_sub_app_mut(RenderApp) {
Ok(render_app) => render_app,
Err(_) => return,
};
render_app
.init_resource::<OtherRenderResource>();
}
fn finish(&self, app: &mut App) {
let render_app = match app.get_sub_app_mut(RenderApp) {
Ok(render_app) => render_app,
Err(_) => return,
};
render_app
.init_resource::<RenderResourceNeedingDevice>();
}
}
```
# Objective
Fixes#8528
## Solution
Manually implement `PartialEq`, `Eq`, `PartialOrd`, `Ord`, and `Hash`
for `bevy_ecs::event::EventId`. These new implementations do not rely on
the `Event` implementing the same traits allowing `EventId` to be used
in more cases.
# Objective
there was a typo in AxisSettings. It said "Values that are higher than
`livezone_upperbound` will be rounded up to -1.0." which I'm pretty
confident should be "1.0".
## Solution
I removed the '-'
# Objective
After fixing dynamic scene to only map specific entities, we want
map_entities to default to the less error prone behavior and have the
previous behavior renamed to "map_all_entities." As this is a breaking
change, it could not be pushed out with the bug fix.
## Solution
Simple rename and refactor.
## Changelog
### Changed
- `map_entities` now accepts a list of entities to apply to, with
`map_all_entities` retaining previous behavior of applying to all
entities in the map.
## Migration Guide
- In `bevy_ecs`, `ReflectMapEntities::map_entites` now requires an
additional `entities` parameter to specify which entities it applies to.
To keep the old behavior, use the new
`ReflectMapEntities::map_all_entities`, but consider if passing the
entities in specifically might be better for your use case to avoid
bugs.
# Objective
- I want to take screenshots of examples in CI to help with validation
of changes
## Solution
- Can override how much time is updated per frame
- Can specify on which frame to take a screenshots
- Save screenshots in CI
I reused the `TimeUpdateStrategy::ManualDuration` to be able to set the
time update strategy to a fixed duration every frame. Its previous
meaning didn't make much sense to me. This change makes it possible to
have screenshots that are exactly the same across runs.
If this gets merged, I'll add visual comparison of screenshots between
runs to ensure nothing gets broken
## Migration Guide
* `TimeUpdateStrategy::ManualDuration` meaning has changed. Instead of
setting time to `Instant::now()` plus the given duration, it sets time
to last update plus the given duration.
# Objective
- For many UI use cases (e.g. tree views, lists), it is important to be
able to imperatively sort child nodes.
- This also enables us to eventually support something like the
[`order`](https://developer.mozilla.org/en-US/docs/Web/CSS/order) CSS
property, that declaratively re-orders flex box items by a numeric
value, similar to z-index, but in space.
## Solution
We removed the ability to directly construct `Children` from `&[Entity]`
some time ago (#4197#5532) to enforce consistent hierarchies ([RFC
53](https://github.com/bevyengine/rfcs/blob/main/rfcs/53-consistent-hierarchy.md)).
If I understand it correctly, it's currently possible to re-order
children by using `Children::swap()` or
`commands.entity(id).replace_children(...)`, however these are either
too cumbersome, needlessly inefficient, and/or don't take effect
immediately.
This PR exposes the in-place sorting methods from the `slice` primitive
in `Children`, enabling imperatively sorting children in place via `&mut
Children`, while still preserving consistent hierarchies.
---
## Changelog
### Added
- The sorting methods from the `slice` primitive are now exposed by the
`Children` component, allowing imperatively sorting children in place
(Useful for UI scenarios such as lists)
# Objective
- Handle dangling entity references inside scenes
- Handle references to entities with generation > 0 inside scenes
- Fix a latent bug in `Parent`'s `MapEntities` implementation, which
would, if the parent was outside the scene, cause the scene to be loaded
into the new world with a parent reference potentially pointing to some
random entity in that new world.
- Fixes#4793 and addresses #7235
## Solution
- DynamicScenes now identify entities with a `Entity` instead of a u32,
therefore including generation
- `World` exposes a new `reserve_generations` function that despawns an
entity and advances its generation by some extra amount.
- `MapEntities` implementations have a new `get_or_reserve` function
available that will always return an `Entity`, establishing a new
mapping to a dead entity when the entity they are called with is not in
the `EntityMap`. Subsequent calls with that same `Entity` will return
the same newly created dead entity reference, preserving equality
semantics.
- As a result, after loading a scene containing references to dead
entities (or entities otherwise outside the scene), those references
will all point to different generations on a single entity id in the new
world.
---
## Changelog
### Changed
- In serialized scenes, entities are now identified by a u64 instead of
a u32.
- In serialized scenes, components with entity references now have those
references serialize as u64s instead of structs.
### Fixed
- Scenes containing components with entity references will now
deserialize and add to a world reliably.
## Migration Guide
- `MapEntities` implementations must change from a `&EntityMap`
parameter to a `&mut EntityMapper` parameter and can no longer return a
`Result`. Finally, they should switch from calling `EntityMap::get` to
calling `EntityMapper::get_or_reserve`.
---------
Co-authored-by: Nicola Papale <nicopap@users.noreply.github.com>
# Objective
fixes#8516
* Give `CalculatedSize` a more specific and intuitive name.
* `MeasureFunc`s should only be updated when their `CalculatedSize` is
modified by the systems managing their content.
For example, suppose that you have a UI displaying an image using an
`ImageNode`. When the window is resized, the node's `MeasureFunc` will
be updated even though the dimensions of the texture contained by the
node are unchanged.
* Fix the `CalculatedSize` API so that it no longer requires the extra
boxing and the `dyn_clone` method.
## Solution
* Rename `CalculatedSize` to `ContentSize`
* Only update `MeasureFunc`s on `CalculatedSize` changes.
* Remove the `dyn_clone` method from `Measure` and move the `Measure`
from the `ContentSize` component rather than cloning it.
* Change the measure_func field of `ContentSize` to type
`Option<taffy::node::MeasureFunc>`. Add a `set` method that wraps the
given measure appropriately.
---
## Changelog
* Renamed `CalculatedSize` to `ContentSize`.
* Replaced `upsert_leaf` with a function `update_measure` that only
updates the node's `MeasureFunc`.
* `MeasureFunc`s are only updated when the `ContentSize` changes and not
when the layout changes.
* Scale factor is no longer applied to the size values passed to the
`MeasureFunc`.
* Remove the `ContentSize` scaling in `text_system`.
* The `dyn_clone` method has been removed from the `Measure` trait.
* `Measure`s are moved from the `ContentSize` component instead of
cloning them.
* Added `set` method to `ContentSize` that replaces the `new` function.
## Migration Guide
* `CalculatedSize` has been renamed to `ContentSize`.
* The `upsert_leaf` function has been removed from `UiSurface` and
replaced with `update_measure` which updates the `MeasureFunc` without
node insertion.
* The `dyn_clone` method has been removed from the `Measure` trait.
* The new function of `CalculatedSize` has been replaced with the method
`set`.
# Objective
after calling `SceneSpawner::spawn_as_child`, the scene spawner system
will always try to attach the scene instance to the parent once it is
loaded, even if the parent has been deleted, causing a panic.
## Solution
check if the parent is still alive, and don't spawn the scene instance
if not.
