//! A custom post processing effect, using two cameras, with one reusing the render texture of the first one.
//! Here a chromatic aberration is applied to a 3d scene containing a rotating cube.
//! This example is useful to implement your own post-processing effect such as
//! edge detection, blur, pixelization, vignette... and countless others.

use bevy::{
    core_pipeline::clear_color::ClearColorConfig,
    prelude::*,
    reflect::TypeUuid,
    render::{
        camera::RenderTarget,
        render_resource::{
            AsBindGroup, Extent3d, ShaderRef, TextureDescriptor, TextureDimension, TextureFormat,
            TextureUsages,
        },
        texture::BevyDefault,
        view::RenderLayers,
    },
    sprite::{Material2d, Material2dPlugin, MaterialMesh2dBundle},
};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugin(Material2dPlugin::<PostProcessingMaterial>::default())
        .add_startup_system(setup)
        .add_system(main_camera_cube_rotator_system)
        .run();
}

/// Marks the first camera cube (rendered to a texture.)
#[derive(Component)]
struct MainCube;

fn setup(
    mut commands: Commands,
    windows: Query<&Window>,
    mut meshes: ResMut<Assets<Mesh>>,
    mut post_processing_materials: ResMut<Assets<PostProcessingMaterial>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
    mut images: ResMut<Assets<Image>>,
) {
    // This assumes we only have a single window
    let window = windows.single();

    let size = Extent3d {
        width: window.resolution.physical_width(),
        height: window.resolution.physical_height(),
        ..default()
    };

    // This is the texture that will be rendered to.
    let mut image = Image {
        texture_descriptor: TextureDescriptor {
            label: None,
            size,
            dimension: TextureDimension::D2,
            format: TextureFormat::bevy_default(),
            mip_level_count: 1,
            sample_count: 1,
            usage: TextureUsages::TEXTURE_BINDING
                | TextureUsages::COPY_DST
                | TextureUsages::RENDER_ATTACHMENT,
        },
        ..default()
    };

    // fill image.data with zeroes
    image.resize(size);

    let image_handle = images.add(image);

    let cube_handle = meshes.add(Mesh::from(shape::Cube { size: 4.0 }));
    let cube_material_handle = materials.add(StandardMaterial {
        base_color: Color::rgb(0.8, 0.7, 0.6),
        reflectance: 0.02,
        unlit: false,
        ..default()
    });

    // The cube that will be rendered to the texture.
    commands.spawn((
        PbrBundle {
            mesh: cube_handle,
            material: cube_material_handle,
            transform: Transform::from_translation(Vec3::new(0.0, 0.0, 1.0)),
            ..default()
        },
        MainCube,
    ));

    // Light
    // NOTE: Currently lights are ignoring render layers - see https://github.com/bevyengine/bevy/issues/3462
    commands.spawn(PointLightBundle {
        transform: Transform::from_translation(Vec3::new(0.0, 0.0, 10.0)),
        ..default()
    });

    // Main camera, first to render
    commands.spawn((
        Camera3dBundle {
            camera_3d: Camera3d {
                clear_color: ClearColorConfig::Custom(Color::WHITE),
                ..default()
            },
            camera: Camera {
                target: RenderTarget::Image(image_handle.clone()),
                ..default()
            },
            transform: Transform::from_translation(Vec3::new(0.0, 0.0, 15.0))
                .looking_at(Vec3::default(), Vec3::Y),
            ..default()
        },
        // Disable UI rendering for the first pass camera. This prevents double rendering of UI at
        // the cost of rendering the UI without any post processing effects.
        UiCameraConfig { show_ui: false },
    ));

    // This specifies the layer used for the post processing camera, which will be attached to the post processing camera and 2d quad.
    let post_processing_pass_layer = RenderLayers::layer((RenderLayers::TOTAL_LAYERS - 1) as u8);

    let quad_handle = meshes.add(Mesh::from(shape::Quad::new(Vec2::new(
        size.width as f32,
        size.height as f32,
    ))));

    // This material has the texture that has been rendered.
    let material_handle = post_processing_materials.add(PostProcessingMaterial {
        source_image: image_handle,
    });

    // Post processing 2d quad, with material using the render texture done by the main camera, with a custom shader.
    commands.spawn((
        MaterialMesh2dBundle {
            mesh: quad_handle.into(),
            material: material_handle,
            transform: Transform {
                translation: Vec3::new(0.0, 0.0, 1.5),
                ..default()
            },
            ..default()
        },
        post_processing_pass_layer,
    ));

    // The post-processing pass camera.
    commands.spawn((
        Camera2dBundle {
            camera: Camera {
                // renders after the first main camera which has default value: 0.
                order: 1,
                ..default()
            },
            ..Camera2dBundle::default()
        },
        post_processing_pass_layer,
    ));
}

/// Rotates the cube rendered by the main camera
fn main_camera_cube_rotator_system(
    time: Res<Time>,
    mut query: Query<&mut Transform, With<MainCube>>,
) {
    for mut transform in &mut query {
        transform.rotate_x(0.55 * time.delta_seconds());
        transform.rotate_z(0.15 * time.delta_seconds());
    }
}

// Region below declares of the custom material handling post processing effect

/// Our custom post processing material
#[derive(AsBindGroup, TypeUuid, Clone)]
#[uuid = "bc2f08eb-a0fb-43f1-a908-54871ea597d5"]
struct PostProcessingMaterial {
    /// In this example, this image will be the result of the main camera.
    #[texture(0)]
    #[sampler(1)]
    source_image: Handle<Image>,
}

impl Material2d for PostProcessingMaterial {
    fn fragment_shader() -> ShaderRef {
        "shaders/custom_material_chromatic_aberration.wgsl".into()
    }
}