lib.rs

#![expect(missing_docs, reason = "Not all docs are written yet, see #3492.")]
#![cfg_attr(docsrs, feature(doc_cfg))]
#![doc(
    html_logo_url = "https://bevy.org/assets/icon.png",
    html_favicon_url = "https://bevy.org/assets/icon.png"
)]

//! 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 [`widget::Button`], [`ImageNode`](widget::ImageNode), [`Text`](prelude::Text) and [`Node`]
//! This UI is laid out with the Flexbox and CSS Grid layout models (see <https://cssreference.io/flexbox/>)

pub mod auto_directional_navigation;
pub mod interaction_states;
pub mod measurement;
pub mod update;
pub mod widget;

pub mod gradients;
#[cfg(feature = "bevy_picking")]
pub mod picking_backend;
pub mod ui_transform;

use bevy_derive::{Deref, DerefMut};
#[cfg(feature = "bevy_picking")]
use bevy_picking::PickingSystems;
use bevy_reflect::{std_traits::ReflectDefault, Reflect};
mod accessibility;
// This module is not re-exported, but is instead made public.
// This is intended to discourage accidental use of the experimental API.
pub mod experimental;
mod focus;
mod geometry;
mod layout;
mod stack;
mod ui_node;

pub use focus::*;
pub use geometry::*;
pub use gradients::*;
pub use interaction_states::{Checkable, Checked, InteractionDisabled, Pressed};
pub use layout::*;
pub use measurement::*;
pub use ui_node::*;
pub use ui_transform::*;

/// The UI prelude.
///
/// This includes the most common types in this crate, re-exported for your convenience.
pub mod prelude {
    #[doc(hidden)]
    #[cfg(feature = "bevy_picking")]
    pub use crate::picking_backend::{UiPickingCamera, UiPickingPlugin, UiPickingSettings};
    #[doc(hidden)]
    pub use crate::widget::{Text, TextShadow, TextUiReader, TextUiWriter};
    #[doc(hidden)]
    pub use {
        crate::{
            geometry::*,
            gradients::*,
            ui_node::*,
            ui_transform::*,
            widget::{Button, ImageNode, Label, NodeImageMode, ViewportNode},
            Interaction, UiScale,
        },
        // `bevy_sprite` re-exports for texture slicing
        bevy_sprite::{BorderRect, SliceScaleMode, SpriteImageMode, TextureSlicer},
        bevy_text::TextBackgroundColor,
    };
}

use bevy_app::{prelude::*, AnimationSystems, HierarchyPropagatePlugin, PropagateSet};
use bevy_camera::CameraUpdateSystems;
use bevy_ecs::prelude::*;
use bevy_input::InputSystems;
use bevy_transform::TransformSystems;
use layout::ui_surface::UiSurface;
use stack::ui_stack_system;
pub use stack::UiStack;
use update::{propagate_ui_target_cameras, update_clipping_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 UiSystems {
    /// After this label, input interactions with UI entities have been updated for this frame.
    ///
    /// Runs in [`PreUpdate`].
    Focus,
    /// All UI systems in [`PostUpdate`] will run in or after this label.
    Prepare,
    /// Propagate UI component values needed by layout.
    Propagate,
    /// Update content requirements before layout.
    Content,
    /// After this label, the ui layout state has been updated.
    ///
    /// Runs in [`PostUpdate`].
    Layout,
    /// UI systems ordered after [`UiSystems::Layout`].
    ///
    /// Runs in [`PostUpdate`].
    PostLayout,
    /// After this label, the [`UiStack`] resource has been updated.
    ///
    /// Runs in [`PostUpdate`].
    Stack,
}

/// 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)]
#[reflect(Resource, Debug, Default)]
pub struct UiScale(pub f32);

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

// Marks systems that can be ambiguous with [`widget::text_system`] if the `bevy_text` feature is enabled.
// See https://github.com/bevyengine/bevy/pull/11391 for more details.
#[derive(SystemSet, Debug, Hash, PartialEq, Eq, Clone)]
struct AmbiguousWithText;

#[derive(SystemSet, Debug, Hash, PartialEq, Eq, Clone)]
struct AmbiguousWithUpdateText2dLayout;

impl Plugin for UiPlugin {
    fn build(&self, app: &mut App) {
        app.init_resource::<UiSurface>()
            .init_resource::<UiScale>()
            .init_resource::<UiStack>()
            .configure_sets(
                PostUpdate,
                (
                    CameraUpdateSystems,
                    UiSystems::Prepare.after(AnimationSystems),
                    UiSystems::Propagate,
                    UiSystems::Content,
                    UiSystems::Layout,
                    UiSystems::PostLayout,
                )
                    .chain(),
            )
            .configure_sets(
                PostUpdate,
                PropagateSet::<ComputedUiTargetCamera>::default().in_set(UiSystems::Propagate),
            )
            .add_plugins(HierarchyPropagatePlugin::<ComputedUiTargetCamera>::new(
                PostUpdate,
            ))
            .configure_sets(
                PostUpdate,
                PropagateSet::<ComputedUiRenderTargetInfo>::default().in_set(UiSystems::Propagate),
            )
            .add_plugins(HierarchyPropagatePlugin::<ComputedUiRenderTargetInfo>::new(
                PostUpdate,
            ))
            .add_systems(
                PreUpdate,
                ui_focus_system.in_set(UiSystems::Focus).after(InputSystems),
            );

        #[cfg(feature = "bevy_picking")]
        app.add_plugins(picking_backend::UiPickingPlugin)
            .add_systems(
                First,
                widget::viewport_picking.in_set(PickingSystems::PostInput),
            );

        let ui_layout_system_config = ui_layout_system
            .in_set(UiSystems::Layout)
            .before(TransformSystems::Propagate);

        let ui_layout_system_config = ui_layout_system_config
            // Text and Text2D operate on disjoint sets of entities
            .ambiguous_with(bevy_sprite::update_text2d_layout)
            .ambiguous_with(bevy_text::detect_text_needs_rerender::<bevy_sprite::Text2d>);

        app.add_systems(
            PostUpdate,
            (
                propagate_ui_target_cameras.in_set(UiSystems::Prepare),
                ui_layout_system_config,
                ui_stack_system
                    .in_set(UiSystems::Stack)
                    // These systems don't care about stack index
                    .ambiguous_with(widget::measure_text_system)
                    .ambiguous_with(update_clipping_system)
                    .ambiguous_with(ui_layout_system)
                    .ambiguous_with(widget::update_viewport_render_target_size)
                    .in_set(AmbiguousWithText),
                update_clipping_system.after(TransformSystems::Propagate),
                // Potential conflicts: `Assets<Image>`
                // They run independently since `widget::image_node_system` will only ever observe
                // its own ImageNode, and `widget::text_system` & `bevy_text::update_text2d_layout`
                // will never modify a pre-existing `Image` asset.
                widget::update_image_content_size_system
                    .in_set(UiSystems::Content)
                    .in_set(AmbiguousWithText)
                    .in_set(AmbiguousWithUpdateText2dLayout),
                // Potential conflicts: `Assets<Image>`
                // `widget::text_system` and `bevy_text::update_text2d_layout` run independently
                // since this system will only ever update viewport images.
                widget::update_viewport_render_target_size
                    .in_set(UiSystems::PostLayout)
                    .in_set(AmbiguousWithText)
                    .in_set(AmbiguousWithUpdateText2dLayout),
            ),
        );

        build_text_interop(app);
    }
}

fn build_text_interop(app: &mut App) {
    use widget::Text;

    app.add_systems(
        PostUpdate,
        (
            (
                bevy_text::detect_text_needs_rerender::<Text>,
                widget::measure_text_system,
            )
                .chain()
                .after(bevy_text::load_font_assets_into_fontdb_system)
                .in_set(UiSystems::Content)
                // Text and Text2d are independent.
                .ambiguous_with(bevy_text::detect_text_needs_rerender::<bevy_sprite::Text2d>)
                // 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_sprite::update_text2d_layout)
                // We assume Text is on disjoint UI entities to ImageNode 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
                .in_set(UiSystems::PostLayout)
                .after(bevy_text::load_font_assets_into_fontdb_system)
                .after(bevy_asset::AssetEventSystems)
                // Text2d and bevy_ui text are entirely on separate entities
                .ambiguous_with(bevy_text::detect_text_needs_rerender::<bevy_sprite::Text2d>)
                .ambiguous_with(bevy_sprite::update_text2d_layout)
                .ambiguous_with(bevy_sprite::calculate_bounds_text2d),
        ),
    );

    app.add_plugins(accessibility::AccessibilityPlugin);

    app.add_observer(interaction_states::on_add_disabled)
        .add_observer(interaction_states::on_remove_disabled)
        .add_observer(interaction_states::on_add_checkable)
        .add_observer(interaction_states::on_remove_checkable)
        .add_observer(interaction_states::on_add_checked)
        .add_observer(interaction_states::on_remove_checked);

    app.configure_sets(
        PostUpdate,
        AmbiguousWithText.ambiguous_with(widget::text_system),
    );

    app.configure_sets(
        PostUpdate,
        AmbiguousWithUpdateText2dLayout.ambiguous_with(bevy_sprite::update_text2d_layout),
    );
}