ShaderType wrapped f32

custom_material.wgsl

struct WrappedF32 {
    [[size(16)]]
    value: f32;
};

struct CustomMaterial {
    data: array<WrappedF32, 4>;
};
[[group(1), binding(0)]]
var<uniform> material: CustomMaterial;

[[stage(fragment)]]
fn fragment() -> [[location(0)]] vec4<f32> {
    return vec4<f32>(
        material.data[0].value,
        material.data[1].value,
        material.data[2].value,
        material.data[3].value
    );
}

main.rs

use bevy::{
    ecs::system::{lifetimeless::SRes, SystemParamItem},
    pbr::MaterialPipeline,
    prelude::*,
    reflect::TypeUuid,
    render::{
        render_asset::{PrepareAssetError, RenderAsset},
        render_resource::{
            encase, BindGroup, BindGroupDescriptor, BindGroupEntry, BindGroupLayout,
            BindGroupLayoutDescriptor, BindGroupLayoutEntry, BindingType, Buffer,
            BufferBindingType, BufferInitDescriptor, BufferUsages, ShaderStages, ShaderType,
        },
        renderer::RenderDevice,
    },
};

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

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<CustomMaterial>>,
) {
    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: materials.add(CustomMaterial {
            data: [
                // RGBA color
                // red works, green or blue gives a black color
                WrappedF32 { value: 1.0 },
                WrappedF32 { value: 0.0 },
                WrappedF32 { value: 0.0 },
                WrappedF32 { value: 1.0 },
            ],
        }),
        ..default()
    });

    commands.spawn_bundle(Camera3dBundle {
        transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
        ..default()
    });
}

#[derive(Debug, Clone, ShaderType)]
struct WrappedF32 {
    #[size(16)]
    value: f32,
}

#[derive(Debug, Clone, TypeUuid, ShaderType)]
#[uuid = "f690fdae-d598-45ab-8225-97e2a3f056e0"]
pub struct CustomMaterial {
    data: [WrappedF32; 4],
}

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

impl RenderAsset for CustomMaterial {
    type ExtractedAsset = CustomMaterial;
    type PreparedAsset = GpuCustomMaterial;
    type Param = (SRes<RenderDevice>, SRes<MaterialPipeline<Self>>);

    fn extract_asset(&self) -> Self::ExtractedAsset {
        self.clone()
    }

    fn prepare_asset(
        extracted_asset: Self::ExtractedAsset,
        (render_device, material_pipeline): &mut SystemParamItem<Self::Param>,
    ) -> Result<Self::PreparedAsset, PrepareAssetError<Self::ExtractedAsset>> {
        let mut buffer = encase::UniformBuffer::new(Vec::new());
        buffer.write(&extracted_asset).unwrap();
        info!("{:?}", extracted_asset);

        let buffer = render_device.create_buffer_with_data(&BufferInitDescriptor {
            contents: buffer.as_ref(),
            label: None,
            usage: BufferUsages::UNIFORM | BufferUsages::COPY_DST,
        });
        let bind_group = render_device.create_bind_group(&BindGroupDescriptor {
            entries: &[BindGroupEntry {
                binding: 0,
                resource: buffer.as_entire_binding(),
            }],
            label: None,
            layout: &material_pipeline.material_layout,
        });

        Ok(GpuCustomMaterial {
            _buffer: buffer,
            bind_group,
        })
    }
}

impl Material for CustomMaterial {
    fn fragment_shader(asset_server: &AssetServer) -> Option<Handle<Shader>> {
        Some(asset_server.load("custom_material.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::Buffer {
                    ty: BufferBindingType::Uniform,
                    has_dynamic_offset: false,
                    min_binding_size: None,
                },
                count: None,
            }],
            label: None,
        })
    }
}