bevy/examples/shader/shader_material_screenspace_texture.rs

use bevy::{
    ecs::system::{lifetimeless::SRes, SystemParamItem},
    pbr::MaterialPipeline,
    prelude::*,
    reflect::TypeUuid,
    render::{
        render_asset::{PrepareAssetError, RenderAsset, RenderAssets},
        render_resource::{
            BindGroup, BindGroupDescriptor, BindGroupEntry, BindGroupLayout,
            BindGroupLayoutDescriptor, BindGroupLayoutEntry, BindingResource, BindingType,
            SamplerBindingType, ShaderStages, TextureSampleType, TextureViewDimension,
        },
        renderer::RenderDevice,
    },
};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugin(MaterialPlugin::<CustomMaterial>::default())
        .add_startup_system(setup)
        .add_system(rotate_camera)
        .run();
}

#[derive(Component)]
struct MainCamera;

fn setup(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
    mut meshes: ResMut<Assets<Mesh>>,
    mut custom_materials: ResMut<Assets<CustomMaterial>>,
    mut standard_materials: ResMut<Assets<StandardMaterial>>,
) {
    commands.spawn_bundle(PbrBundle {
        mesh: meshes.add(Mesh::from(shape::Plane { size: 5.0 })),
        material: standard_materials.add(Color::rgb(0.3, 0.5, 0.3).into()),
        ..default()
    });
    commands.spawn_bundle(PointLightBundle {
        transform: Transform::from_xyz(4.0, 8.0, 4.0),
        ..default()
    });
    commands.spawn_bundle(PerspectiveCameraBundle {
        transform: Transform::from_xyz(0.0, 2.5, 1.0).looking_at(Vec3::default(), Vec3::Y),
        ..default()
    });

    commands.spawn().insert_bundle(MaterialMeshBundle {
        mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
        transform: Transform::from_xyz(0.0, 0.5, 0.0),
        material: custom_materials.add(CustomMaterial {
            texture: asset_server.load(
                "models/FlightHelmet/FlightHelmet_Materials_LensesMat_OcclusionRoughMetal.png",
            ),
        }),
        ..default()
    });

    // camera
    commands
        .spawn_bundle(PerspectiveCameraBundle {
            transform: Transform::from_xyz(4.0, 2.5, 4.0).looking_at(Vec3::ZERO, Vec3::Y),
            ..default()
        })
        .insert(MainCamera);
}

fn rotate_camera(mut camera: Query<&mut Transform, With<MainCamera>>, time: Res<Time>) {
    let cam_transform = camera.single_mut().into_inner();

    cam_transform.rotate_around(
        Vec3::ZERO,
        Quat::from_axis_angle(Vec3::Y, 45f32.to_radians() * time.delta_seconds()),
    );
    cam_transform.look_at(Vec3::ZERO, Vec3::Y);
}

#[derive(Debug, Clone, TypeUuid)]
#[uuid = "b62bb455-a72c-4b56-87bb-81e0554e234f"]
pub struct CustomMaterial {
    texture: Handle<Image>,
}

#[derive(Clone)]
pub struct GpuCustomMaterial {
    bind_group: BindGroup,
}

impl RenderAsset for CustomMaterial {
    type ExtractedAsset = CustomMaterial;
    type PreparedAsset = GpuCustomMaterial;
    type Param = (
        SRes<RenderDevice>,
        SRes<RenderAssets<Image>>,
        SRes<MaterialPipeline<Self>>,
    );
    fn extract_asset(&self) -> Self::ExtractedAsset {
        self.clone()
    }

    fn prepare_asset(
        extracted_asset: Self::ExtractedAsset,
        (render_device, gpu_images, material_pipeline): &mut SystemParamItem<Self::Param>,
    ) -> Result<Self::PreparedAsset, PrepareAssetError<Self::ExtractedAsset>> {
        let gpu_image = match gpu_images.get(&extracted_asset.texture) {
            Some(gpu_image) => gpu_image,
            // if the image isn't loaded yet, try next frame
            None => return Err(PrepareAssetError::RetryNextUpdate(extracted_asset)),
        };

        let bind_group = render_device.create_bind_group(&BindGroupDescriptor {
            entries: &[
                BindGroupEntry {
                    binding: 0,
                    resource: BindingResource::TextureView(&gpu_image.texture_view),
                },
                BindGroupEntry {
                    binding: 1,
                    resource: BindingResource::Sampler(&gpu_image.sampler),
                },
            ],
            label: None,
            layout: &material_pipeline.material_layout,
        });

        Ok(GpuCustomMaterial { bind_group })
    }
}

impl Material for CustomMaterial {
    fn fragment_shader(asset_server: &AssetServer) -> Option<Handle<Shader>> {
        Some(asset_server.load("shaders/custom_material_screenspace_texture.wgsl"))
    }

    fn bind_group(render_asset: &<Self as RenderAsset>::PreparedAsset) -> &BindGroup {
        &render_asset.bind_group
    }

    fn bind_group_layout(render_device: &RenderDevice) -> BindGroupLayout {
        render_device.create_bind_group_layout(&BindGroupLayoutDescriptor {
            entries: &[
                BindGroupLayoutEntry {
                    binding: 0,
                    visibility: ShaderStages::FRAGMENT,
                    ty: BindingType::Texture {
                        sample_type: TextureSampleType::Float { filterable: true },
                        view_dimension: TextureViewDimension::D2,
                        multisampled: false,
                    },
                    count: None,
                },
                BindGroupLayoutEntry {
                    binding: 1,
                    visibility: ShaderStages::FRAGMENT,
                    ty: BindingType::Sampler(SamplerBindingType::Filtering),
                    count: None,
                },
            ],
            label: None,
        })
    }
}