# Objective
Removal events are unwieldy and require some knowledge of when to put systems that need to catch events for them, it is very easy to end up missing one and end up with memory leak-ish issues where you don't clean up after yourself.
## Solution
Consolidate removals with the benefits of `Events<...>` (such as double buffering and per system ticks for reading the events) and reduce the special casing of it, ideally I was hoping to move the removals to a `Resource` in the world, but that seems a bit more rough to implement/maintain because of double mutable borrowing issues.
This doesn't go the full length of change detection esque removal detection a la https://github.com/bevyengine/rfcs/pull/44.
Just tries to make the current workflow a bit more user friendly so detecting removals isn't such a scheduling nightmare.
---
## Changelog
- RemovedComponents<T> is now backed by an `Events<Entity>` for the benefits of double buffering.
## Migration Guide
- Add a `mut` for `removed: RemovedComponents<T>` since we are now modifying an event reader internally.
- Iterating over removed components now requires `&mut removed_components` or `removed_components.iter()` instead of `&removed_components`.
# Objective
- Update winit to 0.28
## Solution
- Small API change
- A security advisory has been added for a unmaintained crate used by a dependency of winit build script for wayland
I didn't do anything for Android support in this PR though it should be fixable, it should be done in a separate one, maybe https://github.com/bevyengine/bevy/pull/6830
---
## Changelog
- `window.always_on_top` has been removed, you can now use `window.window_level`
## Migration Guide
before:
```rust
app.new()
.add_plugins(DefaultPlugins.set(WindowPlugin {
primary_window: Some(Window {
always_on_top: true,
..default()
}),
..default()
}));
```
after:
```rust
app.new()
.add_plugins(DefaultPlugins.set(WindowPlugin {
primary_window: Some(Window {
window_level: bevy:🪟:WindowLevel::AlwaysOnTop,
..default()
}),
..default()
}));
```
# Objective
- Bevy should not have any "internal" execution order ambiguities. These clutter the output of user-facing error reporting, and can result in nasty, nondetermistic, very difficult to solve bugs.
- Verifying this currently involves repeated non-trivial manual work.
## Solution
- [x] add an example to quickly check this
- ~~[ ] ensure that this example panics if there are any unresolved ambiguities~~
- ~~[ ] run the example in CI 😈~~
There's one tricky ambiguity left, between UI and animation. I don't have the tools to fix this without system set configuration, so the remaining work is going to be left to #7267 or another PR after that.
```
2023-01-27T18:38:42.989405Z INFO bevy_ecs::schedule::ambiguity_detection: Execution order ambiguities detected, you might want to add an explicit dependency relation between some of these systems:
* Parallel systems:
-- "bevy_animation::animation_player" and "bevy_ui::flex::flex_node_system"
conflicts: ["bevy_transform::components::transform::Transform"]
```
## Changelog
Resolved internal execution order ambiguities for:
1. Transform propagation (ignored, we need smarter filter checking).
2. Gamepad processing (fixed).
3. bevy_winit's window handling (fixed).
4. Cascaded shadow maps and perspectives (fixed).
Also fixed a desynchronized state bug that could occur when the `Window` component is removed and then added to the same entity in a single frame.
# Objective
- Fix#7315
- Add IME support
## Solution
- Add two new fields to `Window`, to control if IME is enabled and the candidate box position
This allows the use of dead keys which are needed in French, or the full IME experience to type using Pinyin
I also added a basic general text input example that can handle IME input.
https://user-images.githubusercontent.com/8672791/213941353-5ed73a73-5dd1-4e66-a7d6-a69b49694c52.mp4
# Objective
On wasm, bevy applications currently prevent any of the normal browser hotkeys from working normally (Ctrl+R, F12, F5, Ctrl+F5, tab, etc.).
Some of those events you may want to override, perhaps you can hold the tab key for showing in-game stats?
However, if you want to make a well-behaved game, you probably don't want to needlessly prevent that behavior unless you have a good reason.
Secondary motivation: Also, consider the workaround presented here to get audio working: https://developer.chrome.com/blog/web-audio-autoplay/#moving-forward ; It won't work (for keydown events) if we stop event propagation.
## Solution
- Winit has a field that allows it to not stop event propagation, expose it on the window settings to allow the user to choose the desired behavior. Default to `true` for backwards compatibility.
---
## Changelog
- Added `Window::prevent_default_event_handling` . This allows bevy apps to not override default browser behavior on hotkeys like F5, F12, Ctrl+R etc.
# Objective
- Fixes#7294
## Solution
- Do not trigger change detection when setting the cursor position from winit
When moving the cursor continuously, Winit sends events:
- CursorMoved(0)
- CursorMoved(1)
- => start of Bevy schedule execution
- CursorMoved(2)
- CursorMoved(3)
- <= End of Bevy schedule execution
if Bevy schedule runs after the event 1, events 2 and 3 would happen during the execution but would be read only on the next system run. During the execution, the system would detect a change on cursor position, and send back an order to winit to move it back to 1, so event 2 and 3 would be ignored. By bypassing change detection when setting the cursor from winit event, it doesn't trigger sending back that change to winit out of order.
# Objective
- Fixes#7288
- Do not expose access directly to cursor position as it is the physical position, ignoring scale
## Solution
- Make cursor position private
- Expose getter/setter on the window to have access to the scale
# Objective
Fix https://github.com/bevyengine/bevy/issues/4530
- Make it easier to open/close/modify windows by setting them up as `Entity`s with a `Window` component.
- Make multiple windows very simple to set up. (just add a `Window` component to an entity and it should open)
## Solution
- Move all properties of window descriptor to ~components~ a component.
- Replace `WindowId` with `Entity`.
- ~Use change detection for components to update backend rather than events/commands. (The `CursorMoved`/`WindowResized`/... events are kept for user convenience.~
Check each field individually to see what we need to update, events are still kept for user convenience.
---
## Changelog
- `WindowDescriptor` renamed to `Window`.
- Width/height consolidated into a `WindowResolution` component.
- Requesting maximization/minimization is done on the [`Window::state`] field.
- `WindowId` is now `Entity`.
## Migration Guide
- Replace `WindowDescriptor` with `Window`.
- Change `width` and `height` fields in a `WindowResolution`, either by doing
```rust
WindowResolution::new(width, height) // Explicitly
// or using From<_> for tuples for convenience
(1920., 1080.).into()
```
- Replace any `WindowCommand` code to just modify the `Window`'s fields directly and creating/closing windows is now by spawning/despawning an entity with a `Window` component like so:
```rust
let window = commands.spawn(Window { ... }).id(); // open window
commands.entity(window).despawn(); // close window
```
## Unresolved
- ~How do we tell when a window is minimized by a user?~
~Currently using the `Resize(0, 0)` as an indicator of minimization.~
No longer attempting to tell given how finnicky this was across platforms, now the user can only request that a window be maximized/minimized.
## Future work
- Move `exit_on_close` functionality out from windowing and into app(?)
- https://github.com/bevyengine/bevy/issues/5621
- https://github.com/bevyengine/bevy/issues/7099
- https://github.com/bevyengine/bevy/issues/7098
Co-authored-by: Carter Anderson <mcanders1@gmail.com>
# Objective
See:
- https://github.com/bevyengine/bevy/issues/7067#issuecomment-1381982285
- (This does not fully close that issue in my opinion.)
- https://discord.com/channels/691052431525675048/1063454009769340989
## Solution
This merge request adds documentation:
1. Alert users to the fact that `App::run()` might never return and code placed after it might never be executed.
2. Makes `winit::WinitSettings::return_from_run` discoverable.
3. Better explains why `winit::WinitSettings::return_from_run` is discouraged and better links to up-stream docs. on that topic.
4. Adds notes to the `app/return_after_run.rs` example which otherwise promotes a feature that carries caveats.
Furthermore, w.r.t `winit::WinitSettings::return_from_run`:
- Broken links to `winit` docs are fixed.
- Links now point to BOTH `EventLoop::run()` and `EventLoopExtRunReturn::run_return()` which are the salient up-stream pages and make more sense, taken together.
- Collateral damage: "Supported platforms" heading; disambiguation of "run" → `App::run()`; links.
## Future Work
I deliberately structured the "`run()` might not return" section under `App::run()` to allow for alternative patterns (e.g. `AppExit` event, `WindowClosed` event) to be listed or mentioned, beneath it, in the future.
# Objective
- Set the cursor grab mode after the window is built, fix#7007, clean some conversion code.
## Solution
- Set the cursor grab mode after the window is built.
# Objective
Some settings were only applied in windowed mode.
Fix the issue in #6933
# Solution
Always apply the settings.
Co-authored-by: devil-ira <justthecooldude@gmail.com>
# Objective
- Bevy should be usable to create 'overlay' type apps, where the input is not captured by Bevy, but passed down/into a target app, or to allow passive displays/widgets etc.
## Solution
- the `winit:🪟:Window` already has a `set_cursor_hittest()` which basically does this for mouse input events, so I've exposed it (trying to copy the style laid out in the existing wrappings, and added a simple demo.
---
## Changelog
- Added `hittest` to `WindowAttributes`
- Added the `hittest`'s setters/getters
- Modified the `WindowBuilder`
- Modifed the `WindowDescriptor`'s `Default` impl.
- Added an example `cargo run --example fallthrough`
# Objective
Fix android touch events being flipped. Only removed test for android, don't have ios device to test with. Tested with emulator and physical device.
## Solution
Remove check, no longer needed with coordinate change in 0.9
# Objective
I needed a window which is always on top, to create a overlay app.
## Solution
expose the `always_on_top` property of winit in bevy's `WindowDescriptor` as a boolean flag
---
## Changelog
### Added
- add `WindowDescriptor.always_on_top` which configures a window to stay on top.
This reverts commit 8429b6d6ca as discussed in #6522.
I tested that the game_menu example works as it should.
Co-authored-by: devil-ira <justthecooldude@gmail.com>
# Objective
Copy `send_event` and friends from `World` to `WorldCell`.
Clean up `bevy_winit` using `WorldCell::send_event`.
## Changelog
Added `send_event`, `send_event_default`, and `send_event_batch` to `WorldCell`.
Co-authored-by: devil-ira <justthecooldude@gmail.com>
# Objective
- Bevy main crashs on Safari mobile
- On Safari mobile, calling winit_window.set_cursor_grab(true) fails as the API is not implemented (as there is no cursor on Safari mobile, the api doesn't make sense there). I don't know about other mobile browsers
## Solution
- Do not call the api to release cursor grab on window creation, as the cursor is not grabbed anyway at this point
- This is #3617 which was lost in #6218
# Objective
- fix new clippy lints before they get stable and break CI
## Solution
- run `clippy --fix` to auto-fix machine-applicable lints
- silence `clippy::should_implement_trait` for `fn HandleId::default<T: Asset>`
## Changes
- always prefer `format!("{inline}")` over `format!("{}", not_inline)`
- prefer `Box::default` (or `Box::<T>::default` if necessary) over `Box::new(T::default())`
# Objective
- Update `wgpu` to 0.14.0, `naga` to `0.10.0`, `winit` to 0.27.4, `raw-window-handle` to 0.5.0, `ndk` to 0.7.
## Solution
---
## Changelog
### Changed
- Changed `RawWindowHandleWrapper` to `RawHandleWrapper` which wraps both `RawWindowHandle` and `RawDisplayHandle`, which satisfies the `impl HasRawWindowHandle and HasRawDisplayHandle` that `wgpu` 0.14.0 requires.
- Changed `bevy_window::WindowDescriptor`'s `cursor_locked` to `cursor_grab_mode`, change its type from `bool` to `bevy_window::CursorGrabMode`.
## Migration Guide
- Adjust usage of `bevy_window::WindowDescriptor`'s `cursor_locked` to `cursor_grab_mode`, and adjust its type from `bool` to `bevy_window::CursorGrabMode`.
# Objective
- Trying to make it possible to do write tests that don't require a raw window handle.
- Fixes https://github.com/bevyengine/bevy/issues/6106.
## Solution
- Make the interface and type changes. Avoid accessing `None`.
---
## Changelog
- Converted `raw_window_handle` field in both `Window` and `ExtractedWindow` to `Option<RawWindowHandleWrapper>`.
- Revised accessor function `Window::raw_window_handle()` to return `Option<RawWindowHandleWrapper>`.
- Skip conditions in loops that would require a raw window handle (to create a `Surface`, for example).
## Migration Guide
`Window::raw_window_handle()` now returns `Option<RawWindowHandleWrapper>`.
Co-authored-by: targrub <62773321+targrub@users.noreply.github.com>
# Objective
Fixes#5882
## Solution
Per https://github.com/rust-windowing/winit/issues/1705, the root cause is "UIWindow should be created inside UIApplicationMain". Currently, there are two places to create UIWindow, one is Plugin's build function, which is not inside UIApplicationMain. Just comment it out, and it works.
# Objective
Support monitor selection for all window modes.
Fixes#5875.
## Changelog
* Moved `MonitorSelection` out of `WindowPosition::Centered`, into `WindowDescriptor`.
* `WindowPosition::At` is now relative to the monitor instead of being in 'desktop space'.
* Renamed `MonitorSelection::Number` to `MonitorSelection::Index` for clarity.
* Added `WindowMode` to the prelude.
* `Window::set_position` is now relative to a monitor and takes a `MonitorSelection` as argument.
## Migration Guide
`MonitorSelection` was moved out of `WindowPosition::Centered`, into `WindowDescriptor`.
`MonitorSelection::Number` was renamed to `MonitorSelection::Index`.
```rust
// Before
.insert_resource(WindowDescriptor {
position: WindowPosition::Centered(MonitorSelection::Number(1)),
..default()
})
// After
.insert_resource(WindowDescriptor {
monitor: MonitorSelection::Index(1),
position: WindowPosition::Centered,
..default()
})
```
`Window::set_position` now takes a `MonitorSelection` as argument.
```rust
window.set_position(MonitorSelection::Current, position);
```
Co-authored-by: devil-ira <justthecooldude@gmail.com>
# Objective
https://github.com/bevyengine/bevy/pull/503 added these.
I don't know what problem it solved, the PR doesn't say and the code didn't make it obvious to me.
## Solution
AFAIK removing unsafe `Send`/`Sync` impls can't introduce unsoundness.
Yeet.
## Migration Guide
Why tho.
Co-authored-by: devil-ira <justthecooldude@gmail.com>
# Objective
Fixes#5581
## Solution
`Window::scale_factor` already has logic for selecting the overridden or actual scale factor, so use it.
I tested this with the displays I have access to, but more testing would be nice. This seems like a pretty straightforward bug/fix though.
## Changelog
### Fixed
Fixed window centering on high-dpi displays.
*This PR description is an edited copy of #5007, written by @alice-i-cecile.*
# Objective
Follow-up to https://github.com/bevyengine/bevy/pull/2254. The `Resource` trait currently has a blanket implementation for all types that meet its bounds.
While ergonomic, this results in several drawbacks:
* it is possible to make confusing, silent mistakes such as inserting a function pointer (Foo) rather than a value (Foo::Bar) as a resource
* it is challenging to discover if a type is intended to be used as a resource
* we cannot later add customization options (see the [RFC](https://github.com/bevyengine/rfcs/blob/main/rfcs/27-derive-component.md) for the equivalent choice for Component).
* dependencies can use the same Rust type as a resource in invisibly conflicting ways
* raw Rust types used as resources cannot preserve privacy appropriately, as anyone able to access that type can read and write to internal values
* we cannot capture a definitive list of possible resources to display to users in an editor
## Notes to reviewers
* Review this commit-by-commit; there's effectively no back-tracking and there's a lot of churn in some of these commits.
*ira: My commits are not as well organized :')*
* I've relaxed the bound on Local to Send + Sync + 'static: I don't think these concerns apply there, so this can keep things simple. Storing e.g. a u32 in a Local is fine, because there's a variable name attached explaining what it does.
* I think this is a bad place for the Resource trait to live, but I've left it in place to make reviewing easier. IMO that's best tackled with https://github.com/bevyengine/bevy/issues/4981.
## Changelog
`Resource` is no longer automatically implemented for all matching types. Instead, use the new `#[derive(Resource)]` macro.
## Migration Guide
Add `#[derive(Resource)]` to all types you are using as a resource.
If you are using a third party type as a resource, wrap it in a tuple struct to bypass orphan rules. Consider deriving `Deref` and `DerefMut` to improve ergonomics.
`ClearColor` no longer implements `Component`. Using `ClearColor` as a component in 0.8 did nothing.
Use the `ClearColorConfig` in the `Camera3d` and `Camera2d` components instead.
Co-authored-by: Alice <alice.i.cecile@gmail.com>
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: devil-ira <justthecooldude@gmail.com>
Co-authored-by: Carter Anderson <mcanders1@gmail.com>
Resolves#5004. As suggested in the original issue, change tuple types to their corresponding vector type.
## migration guide
Changed the following fields
- `WindowCommand::SetWindowMode.resolution` from `(u32, u32)` to `UVec2`
- `WindowCommand::SetResolution.logical_resolution` from `(f32, f32)` to `Vec2`
Co-authored-by: Daniel Liu <mr.picklepinosaur@gmail.com>
# Objective
- Fixes#4993
## Solution
- ~~Add `centered` property to `WindowDescriptor`~~
- Add `WindowPosition` enum
- `WindowDescriptor.position` is now `WindowPosition` instead of `Option<Vec2>`
- Add `center_window` function to `Window`
## Migration Guide
- If using `WindowDescriptor`, replace `position: None` with `position: WindowPosition::Default` and `position: Some(vec2)` with `WindowPosition::At(vec2)`.
I'm not sure if this is the best approach, so feel free to give any feedback.
Also I'm not sure how `Option`s should be handled in `bevy_winit/src/lib.rs:161`.
Also, on window creation we can't (or at least I couldn't) get `outer_size`, so this doesn't include decorations in calculations.
# Objective
- Make Bevy work on android
## Solution
- Update android metadata and add a few more
- Set the target sdk to 31 as it will soon (in august) be the minimum sdk level for play store
- Remove the custom code to create an activity and use ndk-glue macro instead
- Delay window creation event on android
- Set the example with compatibility settings for wgpu. Those are needed for Bevy to work on my 2019 android tablet
- Add a few details on how to debug in case of failures
- Fix running the example on emulator. This was failing because of the name of the example
Bevy still doesn't work on android with this, audio features need to be disabled because of an ndk-glue version mismatch: rodio depends on 0.6.2, winit on 0.5.2. You can test with:
```
cargo apk run --release --example android_example --no-default-features --features "bevy_winit,render"
```
# Objective
Fix#4958
There was 4 issues:
- this is not true in WASM and on macOS: f28b921209/examples/3d/split_screen.rs (L90)
- ~~I made sure the system was running at least once~~
- I'm sending the event on window creation
- in webgl, setting a viewport has impacts on other render passes
- only in webgl and when there is a custom viewport, I added a render pass without a custom viewport
- shaderdef NO_ARRAY_TEXTURES_SUPPORT was not used by the 2d pipeline
- webgl feature was used but not declared in bevy_sprite, I added it to the Cargo.toml
- shaderdef NO_STORAGE_BUFFERS_SUPPORT was not used by the 2d pipeline
- I added it based on the BufferBindingType
The last commit changes the two last fixes to add the shaderdefs in the shader cache directly instead of needing to do it in each pipeline
Co-authored-by: Carter Anderson <mcanders1@gmail.com>
Currently Bevy's web canvases are "fixed size". They are manually set to specific dimensions. This might be fine for some games and website layouts, but for sites with flexible layouts, or games that want to "fill" the browser window, Bevy doesn't provide the tools needed to make this easy out of the box.
There are third party plugins like [bevy-web-resizer](https://github.com/frewsxcv/bevy-web-resizer/) that listen for window resizes, take the new dimensions, and resize the winit window accordingly. However this only covers a subset of cases and this is common enough functionality that it should be baked into Bevy.
A significant motivating use case here is the [Bevy WASM Examples page](https://bevyengine.org/examples/). This scales the canvas to fit smaller windows (such as mobile). But this approach both breaks winit's mouse events and removes pixel-perfect rendering (which means we might be rendering too many or too few pixels). https://github.com/bevyengine/bevy-website/issues/371
In an ideal world, winit would support this behavior out of the box. But unfortunately that seems blocked for now: https://github.com/rust-windowing/winit/pull/2074. And it builds on the ResizeObserver api, which isn't supported in all browsers yet (and is only supported in very new versions of the popular browsers).
While we wait for a complete winit solution, I've added a `fit_canvas_to_parent` option to WindowDescriptor / Window, which when enabled will listen for window resizes and resize the Bevy canvas/window to fit its parent element. This enables users to scale bevy canvases using arbitrary CSS, by "inheriting" their parents' size. Note that the wrapper element _is_ required because winit overrides the canvas sizing with absolute values on each resize.
There is one limitation worth calling out here: while the majority of canvas resizes will be triggered by window resizes, modifying element layout at runtime (css animations, javascript-driven element changes, dev-tool-injected changes, etc) will not be detected here. I'm not aware of a good / efficient event-driven way to do this outside of the ResizeObserver api. In practice, window-resize-driven canvas resizing should cover the majority of use cases. Users that want to actively poll for element resizes can just do that (or we can build another feature and let people choose based on their specific needs).
I also took the chance to make a couple of minor tweaks:
* Made the `canvas` window setting available on all platforms. Users shouldn't need to deal with cargo feature selection to support web scenarios. We can just ignore the value on non-web platforms. I added documentation that explains this.
* Removed the redundant "initial create windows" handler. With the addition of the code in this pr, the code duplication was untenable.
This enables a number of patterns:
## Easy "fullscreen window" mode for the default canvas
The "parent element" defaults to the `<body>` element.
```rust
app
.insert_resource(WindowDescriptor {
fit_canvas_to_parent: true,
..default()
})
```
And CSS:
```css
html, body {
margin: 0;
height: 100%;
}
```
## Fit custom canvas to "wrapper" parent element
```rust
app
.insert_resource(WindowDescriptor {
fit_canvas_to_parent: true,
canvas: Some("#bevy".to_string()),
..default()
})
```
And the HTML:
```html
<div style="width: 50%; height: 100%">
<canvas id="bevy"></canvas>
</div>
```
# Objective
Fixes#3180, builds from https://github.com/bevyengine/bevy/pull/2898
## Solution
Support requesting a window to be closed and closing a window in `bevy_window`, and handle this in `bevy_winit`.
This is a stopgap until we move to windows as entites, which I'm sure I'll get around to eventually.
## Changelog
### Added
- `Window::close` to allow closing windows.
- `WindowClosed` to allow reacting to windows being closed.
### Changed
Replaced `bevy::system::exit_on_esc_system` with `bevy:🪟:close_on_esc`.
## Fixed
The app no longer exits when any window is closed. This difference is only observable when there are multiple windows.
## Migration Guide
`bevy::input::system::exit_on_esc_system` has been removed. Use `bevy:🪟:close_on_esc` instead.
`CloseWindow` has been removed. Use `Window::close` instead.
The `Close` variant has been added to `WindowCommand`. Handle this by closing the relevant window.
# Objective
- Part of the splitting process of #3692.
## Solution
- Rename `ElementState` to `ButtonState`
## Reasons
- The old name was too generic.
- If something can be pressed it is automatically button-like (thanks to @alice-i-cecile for bringing it up in #3692).
- The reason it is called `ElementState` is because that's how `winit` calls it.
- It is used to define if a keyboard or mouse **button** is pressed or not.
- Discussion in #3692.
## Changelog
### Changed
- The `ElementState` type received a rename and is now called `ButtonState`.
## Migration Guide
- The `ElementState` type received a rename and is now called `ButtonState`. To migrate you just have to change every occurrence of `ElementState` to `ButtonState`.
Co-authored-by: KDecay <KDecayMusic@protonmail.com>
# Objective
- Fixes https://github.com/bevyengine/bevy/issues/2096
## Solution
- This PR enables the drag-and-drop feature for winit on windows again, as the collision issue between cpal and winit has been fixed in https://github.com/RustAudio/cpal/pull/597. I confirmed the drag and drop example working on windows 10 with this change.
- ~~It also bumps the rodio version, though this is not strictly necessary.~~
# Objective
- Improve documentation.
- Provide helper functions for common uses of `Windows` relating to getting the primary `Window`.
- Reduce repeated `Window` code.
# Solution
- Adds infallible `primary()` and `primary_mut()` functions with standard error text. This replaces the commonly used `get_primary().unwrap()` seen throughout bevy which has inconsistent or nonexistent error messages.
- Adds `scale_factor(WindowId)` to replace repeated code blocks throughout.
# Considerations
- The added functions can panic if the primary window does not exist.
- It is very uncommon for the primary window to not exist, as seen by the regular use of `get_primary().unwrap()`. Most users will have a single window and will need to reference the primary window in their code multiple times.
- The panic provides a consistent error message to make this class of error easy to spot from the panic text.
- This follows the established standard of short names for infallible-but-unlikely-to-panic functions in bevy.
- Removes line noise for common usage of `Windows`.
# Objective
- Reduce power usage for games when not focused.
- Reduce power usage to ~0 when a desktop application is minimized (opt-in).
- Reduce power usage when focused, only updating on a `winit` event, or the user sends a redraw request. (opt-in)
https://user-images.githubusercontent.com/2632925/156904387-ec47d7de-7f06-4c6f-8aaf-1e952c1153a2.mp4
Note resource usage in the Task Manager in the above video.
## Solution
- Added a type `UpdateMode` that allows users to specify how the winit event loop is updated, without exposing winit types.
- Added two fields to `WinitConfig`, both with the `UpdateMode` type. One configures how the application updates when focused, and the other configures how the application behaves when it is not focused. Users can modify this resource manually to set the type of event loop control flow they want.
- For convenience, two functions were added to `WinitConfig`, that provide reasonable presets: `game()` (default) and `desktop_app()`.
- The `game()` preset, which is used by default, is unchanged from current behavior with one exception: when the app is out of focus the app updates at a minimum of 10fps, or every time a winit event is received. This has a huge positive impact on power use and responsiveness on my machine, which will otherwise continue running the app at many hundreds of fps when out of focus or minimized.
- The `desktop_app()` preset is fully reactive, only updating when user input (winit event) is supplied or a `RedrawRequest` event is sent. When the app is out of focus, it only updates on `Window` events - i.e. any winit event that directly interacts with the window. What this means in practice is that the app uses *zero* resources when minimized or not interacted with, but still updates fluidly when the app is out of focus and the user mouses over the application.
- Added a `RedrawRequest` event so users can force an update even if there are no events. This is useful in an application when you want to, say, run an animation even when the user isn't providing input.
- Added an example `low_power` to demonstrate these changes
## Usage
Configuring the event loop:
```rs
use bevy::winit::{WinitConfig};
// ...
.insert_resource(WinitConfig::desktop_app()) // preset
// or
.insert_resource(WinitConfig::game()) // preset
// or
.insert_resource(WinitConfig{ .. }) // manual
```
Requesting a redraw:
```rs
use bevy:🪟:RequestRedraw;
// ...
fn request_redraw(mut event: EventWriter<RequestRedraw>) {
event.send(RequestRedraw);
}
```
## Other details
- Because we have a single event loop for multiple windows, every time I've mentioned "focused" above, I more precisely mean, "if at least one bevy window is focused".
- Due to a platform bug in winit (https://github.com/rust-windowing/winit/issues/1619), we can't simply use `Window::request_redraw()`. As a workaround, this PR will temporarily set the window mode to `Poll` when a redraw is requested. This is then reset to the user's `WinitConfig` setting on the next frame.
