Add UI scaling (#5814)

# Objective

- Allow users to change the scaling of the UI
- Adopted from #2808

## Solution

- This is an accessibility feature for fixed-size UI elements, allowing the developer to expose a range of UI scales for the player to set a scale that works for their needs.

> - The user can modify the UiScale struct to change the scaling at runtime. This multiplies the Px values by the scale given, while not touching any others.
> - The example showcases how this even allows for fluid transitions

> Here's how the example looks like:

https://user-images.githubusercontent.com/1631166/132979069-044161a9-8e85-45ab-9e93-fcf8e3852c2b.mp4

---

## Changelog

- Added a `UiScale` which can be used to scale all of UI


Co-authored-by: Andreas Weibye <13300393+Weibye@users.noreply.github.com>
Co-authored-by: Carter Anderson <mcanders1@gmail.com>

Cargo.toml

@@ -1452,6 +1452,16 @@ description = "Illustrates various features of Bevy UI"
 category = "UI (User Interface)"
 wasm = true
 
+[[example]]
+name = "ui_scaling"
+path = "examples/ui/scaling.rs"
+
+[package.metadata.example.ui_scaling]
+name = "UI Scaling"
+description = "Illustrates how to scale the UI"
+category = "UI (User Interface)"
+wasm = true
+
 # Window
 [[example]]
 name = "clear_color"

crates/bevy_ui/src/flex/mod.rs

@@ -1,6 +1,6 @@
 mod convert;
 
-use crate::{CalculatedSize, Node, Style};
+use crate::{CalculatedSize, Node, Style, UiScale};
 use bevy_ecs::{
     entity::Entity,
     event::EventReader,
@@ -196,6 +196,7 @@ pub enum FlexError {
 #[allow(clippy::too_many_arguments)]
 pub fn flex_node_system(
     windows: Res<Windows>,
+    ui_scale: Res<UiScale>,
     mut scale_factor_events: EventReader<WindowScaleFactorChanged>,
     mut flex_surface: ResMut<FlexSurface>,
     root_node_query: Query<Entity, (With<Node>, Without<Parent>)>,
@@ -215,15 +216,12 @@ pub fn flex_node_system(
 
     // assume one window for time being...
     let logical_to_physical_factor = windows.scale_factor(WindowId::primary());
+    let scale_factor = logical_to_physical_factor * ui_scale.scale;
 
-    if scale_factor_events.iter().next_back().is_some() {
-        update_changed(
-            &mut *flex_surface,
-            logical_to_physical_factor,
-            full_node_query,
-        );
+    if scale_factor_events.iter().next_back().is_some() || ui_scale.is_changed() {
+        update_changed(&mut *flex_surface, scale_factor, full_node_query);
     } else {
-        update_changed(&mut *flex_surface, logical_to_physical_factor, node_query);
+        update_changed(&mut *flex_surface, scale_factor, node_query);
     }
 
     fn update_changed<F: WorldQuery>(
@@ -243,7 +241,7 @@ pub fn flex_node_system(
     }
 
     for (entity, style, calculated_size) in &changed_size_query {
-        flex_surface.upsert_leaf(entity, style, *calculated_size, logical_to_physical_factor);
+        flex_surface.upsert_leaf(entity, style, *calculated_size, scale_factor);
     }
 
     // TODO: handle removed nodes

crates/bevy_ui/src/lib.rs

@@ -22,11 +22,14 @@ pub use ui_node::*;
 #[doc(hidden)]
 pub mod prelude {
     #[doc(hidden)]
-    pub use crate::{entity::*, geometry::*, ui_node::*, widget::Button, Interaction};
+    pub use crate::{entity::*, geometry::*, ui_node::*, widget::Button, Interaction, UiScale};
 }
 
 use bevy_app::prelude::*;
-use bevy_ecs::schedule::{ParallelSystemDescriptorCoercion, SystemLabel};
+use bevy_ecs::{
+    schedule::{ParallelSystemDescriptorCoercion, SystemLabel},
+    system::Resource,
+};
 use bevy_input::InputSystem;
 use bevy_transform::TransformSystem;
 use bevy_window::ModifiesWindows;
@@ -47,10 +50,27 @@ pub enum UiSystem {
     Focus,
 }
 
+/// The current scale of the UI.
+///
+/// A multiplier to fixed-sized ui values.
+/// **Note:** This will only affect fixed ui values like [`Val::Px`]
+#[derive(Debug, Resource)]
+pub struct UiScale {
+    /// The scale to be applied.
+    pub scale: f64,
+}
+
+impl Default for UiScale {
+    fn default() -> Self {
+        Self { scale: 1.0 }
+    }
+}
+
 impl Plugin for UiPlugin {
     fn build(&self, app: &mut App) {
         app.add_plugin(ExtractComponentPlugin::<UiCameraConfig>::default())
             .init_resource::<FlexSurface>()
+            .init_resource::<UiScale>()
             .register_type::<AlignContent>()
             .register_type::<AlignItems>()
             .register_type::<AlignSelf>()

crates/bevy_ui/src/widget/text.rs

@@ -1,4 +1,4 @@
-use crate::{CalculatedSize, Size, Style, Val};
+use crate::{CalculatedSize, Size, Style, UiScale, Val};
 use bevy_asset::Assets;
 use bevy_ecs::{
     entity::Entity,
@@ -9,7 +9,7 @@ use bevy_math::Vec2;
 use bevy_render::texture::Image;
 use bevy_sprite::TextureAtlas;
 use bevy_text::{DefaultTextPipeline, Font, FontAtlasSet, Text, TextError};
-use bevy_window::{WindowId, Windows};
+use bevy_window::Windows;
 
 #[derive(Debug, Default)]
 pub struct QueuedText {
@@ -43,6 +43,7 @@ pub fn text_system(
     mut textures: ResMut<Assets<Image>>,
     fonts: Res<Assets<Font>>,
     windows: Res<Windows>,
+    ui_scale: Res<UiScale>,
     mut texture_atlases: ResMut<Assets<TextureAtlas>>,
     mut font_atlas_set_storage: ResMut<Assets<FontAtlasSet>>,
     mut text_pipeline: ResMut<DefaultTextPipeline>,
@@ -52,7 +53,13 @@ pub fn text_system(
         Query<(&Text, &Style, &mut CalculatedSize)>,
     )>,
 ) {
-    let scale_factor = windows.scale_factor(WindowId::primary());
+    // TODO: This should support window-independent scale settings.
+    // See https://github.com/bevyengine/bevy/issues/5621
+    let scale_factor = if let Some(window) = windows.get_primary() {
+        window.scale_factor() * ui_scale.scale
+    } else {
+        ui_scale.scale
+    };
 
     let inv_scale_factor = 1. / scale_factor;
 

examples/README.md

@@ -313,6 +313,7 @@ Example | Description
 [Text Debug](../examples/ui/text_debug.rs) | An example for debugging text layout
 [Transparency UI](../examples/ui/transparency_ui.rs) | Demonstrates transparency for UI
 [UI](../examples/ui/ui.rs) | Illustrates various features of Bevy UI
+[UI Scaling](../examples/ui/scaling.rs) | Illustrates how to scale the UI
 
 ## Window
 

examples/ui/scaling.rs

@@ -0,0 +1,144 @@
+//! This example illustrates the [`UIScale`] resource from `bevy_ui`.
+
+use bevy::{prelude::*, utils::Duration};
+
+const SCALE_TIME: u64 = 400;
+
+#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq, SystemLabel)]
+struct ApplyScaling;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .insert_resource(TargetScale {
+            start_scale: 1.0,
+            target_scale: 1.0,
+            target_time: Timer::new(Duration::from_millis(SCALE_TIME), false),
+        })
+        .add_startup_system(setup)
+        .add_system(apply_scaling.label(ApplyScaling))
+        .add_system(change_scaling.before(ApplyScaling))
+        .run();
+}
+
+fn setup(mut commands: Commands, asset_server: ResMut<AssetServer>) {
+    commands.spawn_bundle(Camera2dBundle::default());
+
+    let text_style = TextStyle {
+        font: asset_server.load("fonts/FiraMono-Medium.ttf"),
+        font_size: 16.,
+        color: Color::BLACK,
+    };
+
+    commands
+        .spawn_bundle(NodeBundle {
+            style: Style {
+                size: Size::new(Val::Percent(50.0), Val::Percent(50.0)),
+                position_type: PositionType::Absolute,
+                position: UiRect {
+                    left: Val::Percent(25.),
+                    top: Val::Percent(25.),
+                    ..default()
+                },
+                justify_content: JustifyContent::SpaceAround,
+                align_items: AlignItems::Center,
+                ..default()
+            },
+            color: Color::ANTIQUE_WHITE.into(),
+            ..default()
+        })
+        .with_children(|parent| {
+            parent
+                .spawn_bundle(NodeBundle {
+                    style: Style {
+                        size: Size::new(Val::Px(40.), Val::Px(40.)),
+                        ..default()
+                    },
+                    color: Color::RED.into(),
+                    ..default()
+                })
+                .with_children(|parent| {
+                    parent.spawn_bundle(TextBundle::from_section("Size!", text_style));
+                });
+            parent.spawn_bundle(NodeBundle {
+                style: Style {
+                    size: Size::new(Val::Percent(15.), Val::Percent(15.)),
+                    ..default()
+                },
+                color: Color::BLUE.into(),
+                ..default()
+            });
+            parent.spawn_bundle(ImageBundle {
+                style: Style {
+                    size: Size::new(Val::Px(30.0), Val::Px(30.0)),
+                    ..default()
+                },
+                image: asset_server.load("branding/icon.png").into(),
+                ..default()
+            });
+        });
+}
+
+/// System that changes the scale of the ui when pressing up or down on the keyboard.
+fn change_scaling(input: Res<Input<KeyCode>>, mut ui_scale: ResMut<TargetScale>) {
+    if input.just_pressed(KeyCode::Up) {
+        let scale = (ui_scale.target_scale * 2.0).min(8.);
+        ui_scale.set_scale(scale);
+        info!("Scaling up! Scale: {}", ui_scale.target_scale);
+    }
+    if input.just_pressed(KeyCode::Down) {
+        let scale = (ui_scale.target_scale / 2.0).max(1. / 8.);
+        ui_scale.set_scale(scale);
+        info!("Scaling down! Scale: {}", ui_scale.target_scale);
+    }
+}
+
+#[derive(Resource)]
+struct TargetScale {
+    start_scale: f64,
+    target_scale: f64,
+    target_time: Timer,
+}
+
+impl TargetScale {
+    fn set_scale(&mut self, scale: f64) {
+        self.start_scale = self.current_scale();
+        self.target_scale = scale;
+        self.target_time.reset();
+    }
+
+    fn current_scale(&self) -> f64 {
+        let completion = self.target_time.percent();
+        let multiplier = ease_in_expo(completion as f64);
+        self.start_scale + (self.target_scale - self.start_scale) * multiplier
+    }
+
+    fn tick(&mut self, delta: Duration) -> &Self {
+        self.target_time.tick(delta);
+        self
+    }
+
+    fn already_completed(&self) -> bool {
+        self.target_time.finished() && !self.target_time.just_finished()
+    }
+}
+
+fn apply_scaling(
+    time: Res<Time>,
+    mut target_scale: ResMut<TargetScale>,
+    mut ui_scale: ResMut<UiScale>,
+) {
+    if target_scale.tick(time.delta()).already_completed() {
+        return;
+    }
+
+    ui_scale.scale = target_scale.current_scale();
+}
+
+fn ease_in_expo(x: f64) -> f64 {
+    if x == 0. {
+        0.
+    } else {
+        (2.0f64).powf(5. * x - 5.)
+    }
+}