extract_component.rs

use crate::{
    render_resource::{encase::internal::WriteInto, DynamicUniformBuffer, ShaderType},
    renderer::{RenderDevice, RenderQueue},
    sync_component::{SyncComponent, SyncComponentPlugin},
    sync_world::RenderEntity,
    Extract, ExtractSchedule, Render, RenderApp, RenderSystems,
};
use bevy_app::{App, Plugin};
use bevy_camera::visibility::ViewVisibility;
use bevy_ecs::{
    component::Component,
    prelude::*,
    query::{QueryFilter, QueryItem, ReadOnlyQueryData},
};
use core::{marker::PhantomData, ops::Deref};

pub use bevy_render_macros::ExtractComponent;

/// Stores the index of a uniform inside of [`ComponentUniforms`].
#[derive(Component)]
pub struct DynamicUniformIndex<C: Component> {
    index: u32,
    marker: PhantomData<C>,
}

impl<C: Component> DynamicUniformIndex<C> {
    #[inline]
    pub fn index(&self) -> u32 {
        self.index
    }
}

/// Describes how a component gets extracted for rendering.
///
/// Therefore the component is transferred from the "app world" into the "render
/// world" in the [`ExtractSchedule`] step. This functionality is enabled by
/// adding [`ExtractComponentPlugin`] with the component type.
///
/// The Out type is defined in [`SyncComponent`].
///
/// The marker type is only used as a way to bypass the orphan rules. To
/// implement the trait for a foreign type you can use a local type as the
/// marker, e.g. the type of the plugin that calls [`ExtractComponentPlugin`].
pub trait ExtractComponent<Marker = ()>: SyncComponent {
    /// ECS [`ReadOnlyQueryData`] to fetch the components to extract.
    type QueryData: ReadOnlyQueryData;
    /// Filters the entities with additional constraints.
    type QueryFilter: QueryFilter;

    /// Defines how the component is transferred into the "render world".
    fn extract_component(item: QueryItem<'_, '_, Self::QueryData>) -> Option<Self::Out>;
}

/// This plugin prepares the components of the corresponding type for the GPU
/// by transforming them into uniforms.
///
/// They can then be accessed from the [`ComponentUniforms`] resource.
/// For referencing the newly created uniforms a [`DynamicUniformIndex`] is inserted
/// for every processed entity.
///
/// Therefore it sets up the [`RenderSystems::Prepare`] step
/// for the specified [`ExtractComponent`].
pub struct UniformComponentPlugin<C>(PhantomData<fn() -> C>);

impl<C> Default for UniformComponentPlugin<C> {
    fn default() -> Self {
        Self(PhantomData)
    }
}

impl<C: Component + ShaderType + WriteInto + Clone> Plugin for UniformComponentPlugin<C> {
    fn build(&self, app: &mut App) {
        if let Some(render_app) = app.get_sub_app_mut(RenderApp) {
            render_app
                .insert_resource(ComponentUniforms::<C>::default())
                .add_systems(
                    Render,
                    prepare_uniform_components::<C>.in_set(RenderSystems::PrepareResources),
                );
        }
    }
}

/// Stores all uniforms of the component type.
#[derive(Resource)]
pub struct ComponentUniforms<C: Component + ShaderType> {
    uniforms: DynamicUniformBuffer<C>,
}

impl<C: Component + ShaderType> Deref for ComponentUniforms<C> {
    type Target = DynamicUniformBuffer<C>;

    #[inline]
    fn deref(&self) -> &Self::Target {
        &self.uniforms
    }
}

impl<C: Component + ShaderType> ComponentUniforms<C> {
    #[inline]
    pub fn uniforms(&self) -> &DynamicUniformBuffer<C> {
        &self.uniforms
    }
}

impl<C: Component + ShaderType> Default for ComponentUniforms<C> {
    fn default() -> Self {
        Self {
            uniforms: Default::default(),
        }
    }
}

/// This system prepares all components of the corresponding component type.
/// They are transformed into uniforms and stored in the [`ComponentUniforms`] resource.
fn prepare_uniform_components<C>(
    mut commands: Commands,
    render_device: Res<RenderDevice>,
    render_queue: Res<RenderQueue>,
    mut component_uniforms: ResMut<ComponentUniforms<C>>,
    components: Query<(Entity, &C)>,
) where
    C: Component + ShaderType + WriteInto + Clone,
{
    let components_iter = components.iter();
    let count = components_iter.len();
    let Some(mut writer) =
        component_uniforms
            .uniforms
            .get_writer(count, &render_device, &render_queue)
    else {
        return;
    };
    let entities = components_iter
        .map(|(entity, component)| {
            (
                entity,
                DynamicUniformIndex::<C> {
                    index: writer.write(component),
                    marker: PhantomData,
                },
            )
        })
        .collect::<Vec<_>>();
    commands.try_insert_batch(entities);
}

/// This plugin extracts the components into the render world for synced
/// entities. To do so, it sets up the [`ExtractSchedule`] step for the
/// specified [`ExtractComponent`].
///
/// It also registers [`SyncComponentPlugin`] to ensure the extracted components
/// are deleted if the main world components are removed.
pub struct ExtractComponentPlugin<C, F = ()> {
    only_extract_visible: bool,
    marker: PhantomData<fn() -> (C, F)>,
}

impl<C, F> Default for ExtractComponentPlugin<C, F> {
    fn default() -> Self {
        Self {
            only_extract_visible: false,
            marker: PhantomData,
        }
    }
}

impl<C, F> ExtractComponentPlugin<C, F> {
    pub fn extract_visible() -> Self {
        Self {
            only_extract_visible: true,
            marker: PhantomData,
        }
    }
}

impl<C: ExtractComponent<Marker>, Marker: 'static> Plugin for ExtractComponentPlugin<C, Marker> {
    fn build(&self, app: &mut App) {
        app.add_plugins(SyncComponentPlugin::<C>::default());

        if let Some(render_app) = app.get_sub_app_mut(RenderApp) {
            if self.only_extract_visible {
                render_app.add_systems(ExtractSchedule, extract_visible_components::<C, Marker>);
            } else {
                render_app.add_systems(ExtractSchedule, extract_components::<C, Marker>);
            }
        }
    }
}

/// This system extracts all components of the corresponding [`ExtractComponent`], for entities that are synced via [`crate::sync_world::SyncToRenderWorld`].
fn extract_components<C: ExtractComponent<Marker>, Marker>(
    mut commands: Commands,
    mut previous_len: Local<usize>,
    query: Extract<Query<(RenderEntity, C::QueryData), C::QueryFilter>>,
) {
    let mut values = Vec::with_capacity(*previous_len);
    for (entity, query_item) in &query {
        if let Some(component) = C::extract_component(query_item) {
            values.push((entity, component));
        } else {
            commands.entity(entity).remove::<C::Out>();
        }
    }
    *previous_len = values.len();
    commands.try_insert_batch(values);
}

/// This system extracts all components of the corresponding [`ExtractComponent`], for entities that are visible and synced via [`crate::sync_world::SyncToRenderWorld`].
fn extract_visible_components<C: ExtractComponent<Marker>, Marker>(
    mut commands: Commands,
    mut previous_len: Local<usize>,
    query: Extract<Query<(RenderEntity, &ViewVisibility, C::QueryData), C::QueryFilter>>,
) {
    let mut values = Vec::with_capacity(*previous_len);
    for (entity, view_visibility, query_item) in &query {
        if view_visibility.get() {
            if let Some(component) = C::extract_component(query_item) {
                values.push((entity, component));
            } else {
                commands.entity(entity).remove::<C::Out>();
            }
        }
    }
    *previous_len = values.len();
    commands.try_insert_batch(values);
}