mod.rs

use bevy_app::prelude::*;
use bevy_asset::{embedded_asset, AssetApp, Assets, Handle};
use bevy_ecs::prelude::*;
use bevy_render::{
    extract_component::ExtractComponentPlugin,
    render_asset::RenderAssetPlugin,
    render_graph::RenderGraphExt,
    render_resource::{
        Buffer, BufferDescriptor, BufferUsages, PipelineCache, SpecializedComputePipelines,
    },
    renderer::RenderDevice,
    ExtractSchedule, Render, RenderApp, RenderStartup, RenderSystems,
};

mod buffers;
mod compensation_curve;
mod node;
mod pipeline;
mod settings;

use buffers::{extract_buffers, prepare_buffers, AutoExposureBuffers};
pub use compensation_curve::{AutoExposureCompensationCurve, AutoExposureCompensationCurveError};
use node::AutoExposureNode;
use pipeline::{AutoExposurePass, AutoExposurePipeline, ViewAutoExposurePipeline};
pub use settings::AutoExposure;

use crate::auto_exposure::{
    compensation_curve::GpuAutoExposureCompensationCurve, pipeline::init_auto_exposure_pipeline,
};
use bevy_core_pipeline::core_3d::graph::{Core3d, Node3d};

/// Plugin for the auto exposure feature.
///
/// See [`AutoExposure`] for more details.
pub struct AutoExposurePlugin;

#[derive(Resource)]
struct AutoExposureResources {
    histogram: Buffer,
}

impl Plugin for AutoExposurePlugin {
    fn build(&self, app: &mut App) {
        embedded_asset!(app, "auto_exposure.wgsl");

        app.add_plugins(RenderAssetPlugin::<GpuAutoExposureCompensationCurve>::default())
            .init_asset::<AutoExposureCompensationCurve>()
            .register_asset_reflect::<AutoExposureCompensationCurve>();
        app.world_mut()
            .resource_mut::<Assets<AutoExposureCompensationCurve>>()
            .insert(&Handle::default(), AutoExposureCompensationCurve::default())
            .unwrap();

        app.add_plugins(ExtractComponentPlugin::<AutoExposure>::default());

        let Some(render_app) = app.get_sub_app_mut(RenderApp) else {
            return;
        };

        render_app
            .init_resource::<SpecializedComputePipelines<AutoExposurePipeline>>()
            .init_resource::<AutoExposureBuffers>()
            .add_systems(
                RenderStartup,
                (init_auto_exposure_pipeline, init_auto_exposure_resources),
            )
            .add_systems(ExtractSchedule, extract_buffers)
            .add_systems(
                Render,
                (
                    prepare_buffers.in_set(RenderSystems::Prepare),
                    queue_view_auto_exposure_pipelines.in_set(RenderSystems::Queue),
                ),
            )
            .add_render_graph_node::<AutoExposureNode>(Core3d, node::AutoExposure)
            .add_render_graph_edges(
                Core3d,
                (
                    Node3d::StartMainPassPostProcessing,
                    node::AutoExposure,
                    Node3d::Tonemapping,
                ),
            );
    }
}

pub fn init_auto_exposure_resources(mut commands: Commands, render_device: Res<RenderDevice>) {
    commands.insert_resource(AutoExposureResources {
        histogram: render_device.create_buffer(&BufferDescriptor {
            label: Some("histogram buffer"),
            size: pipeline::HISTOGRAM_BIN_COUNT * 4,
            usage: BufferUsages::STORAGE,
            mapped_at_creation: false,
        }),
    });
}

fn queue_view_auto_exposure_pipelines(
    mut commands: Commands,
    pipeline_cache: Res<PipelineCache>,
    mut compute_pipelines: ResMut<SpecializedComputePipelines<AutoExposurePipeline>>,
    pipeline: Res<AutoExposurePipeline>,
    view_targets: Query<(Entity, &AutoExposure)>,
) {
    for (entity, auto_exposure) in view_targets.iter() {
        let histogram_pipeline =
            compute_pipelines.specialize(&pipeline_cache, &pipeline, AutoExposurePass::Histogram);
        let average_pipeline =
            compute_pipelines.specialize(&pipeline_cache, &pipeline, AutoExposurePass::Average);

        commands.entity(entity).insert(ViewAutoExposurePipeline {
            histogram_pipeline,
            mean_luminance_pipeline: average_pipeline,
            compensation_curve: auto_exposure.compensation_curve.clone(),
            metering_mask: auto_exposure.metering_mask.clone(),
        });
    }
}