bevy/crates/bevy_ui/src/lib.rs

//! This crate contains Bevy's UI system, which can be used to create UI for both 2D and 3D games
//! # Basic usage
//! Spawn UI elements with [`node_bundles::ButtonBundle`], [`node_bundles::ImageBundle`], [`node_bundles::TextBundle`] and [`node_bundles::NodeBundle`]
//! This UI is laid out with the Flexbox and CSS Grid layout models (see <https://cssreference.io/flexbox/>)

pub mod measurement;
pub mod node_bundles;
pub mod ui_material;
pub mod update;
pub mod widget;

use bevy_derive::{Deref, DerefMut};
use bevy_reflect::Reflect;
#[cfg(feature = "bevy_text")]
use bevy_text::TextLayoutInfo;
#[cfg(feature = "bevy_text")]
mod accessibility;
mod focus;
mod geometry;
mod layout;
mod render;
mod stack;
mod ui_node;

pub use focus::*;
pub use geometry::*;
pub use layout::*;
pub use measurement::*;
pub use render::*;
pub use ui_material::*;
pub use ui_node::*;
use widget::UiImageSize;

#[doc(hidden)]
pub mod prelude {
    #[doc(hidden)]
    pub use crate::{
        geometry::*, node_bundles::*, ui_material::*, ui_node::*, widget::Button, widget::Label,
        Interaction, UiMaterialPlugin, UiScale,
    };
}

#[cfg(feature = "bevy_text")]
use crate::widget::TextFlags;
use bevy_app::prelude::*;
use bevy_ecs::prelude::*;
use bevy_input::InputSystem;
use bevy_render::RenderApp;
use bevy_transform::TransformSystem;
use stack::ui_stack_system;
pub use stack::UiStack;
use update::{update_clipping_system, update_target_camera_system};

/// The basic plugin for Bevy UI
#[derive(Default)]
pub struct UiPlugin;

/// The label enum labeling the types of systems in the Bevy UI
#[derive(Debug, Hash, PartialEq, Eq, Clone, SystemSet)]
pub enum UiSystem {
    /// After this label, the ui layout state has been updated
    Layout,
    /// After this label, input interactions with UI entities have been updated for this frame
    Focus,
    /// After this label, the [`UiStack`] resource has been updated
    Stack,
    /// After this label, node outline widths have been updated
    Outlines,
}

/// 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, Reflect, Resource, Deref, DerefMut)]
pub struct UiScale(pub f32);

impl Default for UiScale {
    fn default() -> Self {
        Self(1.0)
    }
}

impl Plugin for UiPlugin {
    fn build(&self, app: &mut App) {
        app.init_resource::<UiSurface>()
            .init_resource::<UiScale>()
            .init_resource::<UiStack>()
            .register_type::<AlignContent>()
            .register_type::<AlignItems>()
            .register_type::<AlignSelf>()
            .register_type::<BackgroundColor>()
            .register_type::<CalculatedClip>()
            .register_type::<ContentSize>()
            .register_type::<Direction>()
            .register_type::<Display>()
            .register_type::<FlexDirection>()
            .register_type::<FlexWrap>()
            .register_type::<FocusPolicy>()
            .register_type::<GridAutoFlow>()
            .register_type::<GridPlacement>()
            .register_type::<GridTrack>()
            .register_type::<Interaction>()
            .register_type::<JustifyContent>()
            .register_type::<JustifyItems>()
            .register_type::<JustifySelf>()
            .register_type::<Node>()
            // NOTE: used by Style::aspect_ratio
            .register_type::<Option<f32>>()
            .register_type::<Overflow>()
            .register_type::<OverflowAxis>()
            .register_type::<PositionType>()
            .register_type::<RelativeCursorPosition>()
            .register_type::<RepeatedGridTrack>()
            .register_type::<Style>()
            .register_type::<TargetCamera>()
            .register_type::<UiImage>()
            .register_type::<UiImageSize>()
            .register_type::<UiRect>()
            .register_type::<UiScale>()
            .register_type::<Val>()
            .register_type::<BorderColor>()
            .register_type::<widget::Button>()
            .register_type::<widget::Label>()
            .register_type::<ZIndex>()
            .register_type::<Outline>()
            .add_systems(
                PreUpdate,
                ui_focus_system.in_set(UiSystem::Focus).after(InputSystem),
            );

        #[cfg(feature = "bevy_text")]
        app.register_type::<TextLayoutInfo>()
            .register_type::<TextFlags>();
        // add these systems to front because these must run before transform update systems
        #[cfg(feature = "bevy_text")]
        app.add_systems(
            PostUpdate,
            (
                widget::measure_text_system
                    .before(UiSystem::Layout)
                    // Potential conflict: `Assets<Image>`
                    // In practice, they run independently since `bevy_render::camera_update_system`
                    // will only ever observe its own render target, and `widget::measure_text_system`
                    // will never modify a pre-existing `Image` asset.
                    .ambiguous_with(bevy_render::camera::CameraUpdateSystem)
                    // Potential conflict: `Assets<Image>`
                    // Since both systems will only ever insert new [`Image`] assets,
                    // they will never observe each other's effects.
                    .ambiguous_with(bevy_text::update_text2d_layout)
                    // We assume Text is on disjoint UI entities to UiImage and UiTextureAtlasImage
                    // FIXME: Add an archetype invariant for this https://github.com/bevyengine/bevy/issues/1481.
                    .ambiguous_with(widget::update_image_content_size_system),
                widget::text_system
                    .after(UiSystem::Layout)
                    .after(bevy_text::remove_dropped_font_atlas_sets)
                    // Text2d and bevy_ui text are entirely on separate entities
                    .ambiguous_with(bevy_text::update_text2d_layout),
            ),
        );
        #[cfg(feature = "bevy_text")]
        app.add_plugins(accessibility::AccessibilityPlugin);
        app.add_systems(PostUpdate, {
            let system = widget::update_image_content_size_system.before(UiSystem::Layout);
            // Potential conflicts: `Assets<Image>`
            // They run independently since `widget::image_node_system` will only ever observe
            // its own UiImage, and `widget::text_system` & `bevy_text::update_text2d_layout`
            // will never modify a pre-existing `Image` asset.
            #[cfg(feature = "bevy_text")]
            let system = system
                .ambiguous_with(bevy_text::update_text2d_layout)
                .ambiguous_with(widget::text_system);

            system
        });

        app.add_systems(
            PostUpdate,
            (
                update_target_camera_system.before(UiSystem::Layout),
                apply_deferred
                    .after(update_target_camera_system)
                    .before(UiSystem::Layout),
                ui_layout_system
                    .in_set(UiSystem::Layout)
                    .before(TransformSystem::TransformPropagate),
                resolve_outlines_system
                    .in_set(UiSystem::Outlines)
                    .after(UiSystem::Layout)
                    // clipping doesn't care about outlines
                    .ambiguous_with(update_clipping_system)
                    .ambiguous_with(widget::text_system),
                ui_stack_system
                    .in_set(UiSystem::Stack)
                    // the systems don't care about stack index
                    .ambiguous_with(update_clipping_system)
                    .ambiguous_with(resolve_outlines_system)
                    .ambiguous_with(ui_layout_system)
                    .ambiguous_with(widget::text_system),
                update_clipping_system.after(TransformSystem::TransformPropagate),
            ),
        );

        build_ui_render(app);
    }

    fn finish(&self, app: &mut App) {
        let Ok(render_app) = app.get_sub_app_mut(RenderApp) else {
            return;
        };

        render_app.init_resource::<UiPipeline>();
    }
}