perceptual_roughness.md

Perceptual Roughness

For each metal object in our 3D scene, we can see a highlight. The range of this highlight can be controlled.

We use perceptual_roughness of StandardMaterial to control the range of highlight.

commands.spawn(PbrBundle {
    material: materials.add(StandardMaterial {
        perceptual_roughness: 1.,
        ..default()
    }),
    ..default()
});

The value of perceptual_roughness is between 0.089 and 1. The larger the value, the larger the range of highlight.

In the following example, we create three spheres. From the left to right, their perceptual_roughness are 0.089, 0.5 and 1 respectively. To make the difference obvious, we set all metallic to 1.

The full code is as follows:

use bevy::{
    app::{App, Startup},
    asset::Assets,
    core_pipeline::core_3d::Camera3dBundle,
    ecs::system::{Commands, ResMut},
    math::Vec3,
    pbr::{DirectionalLight, DirectionalLightBundle, PbrBundle, StandardMaterial},
    render::mesh::{
        shape::{Plane, UVSphere},
        Mesh,
    },
    transform::components::Transform,
    utils::default,
    DefaultPlugins,
};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .run();
}

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    commands.spawn(Camera3dBundle {
        transform: Transform::from_xyz(0., 2., 3.).looking_at(Vec3::new(0., 0.5, 0.), Vec3::Y),
        ..default()
    });

    // left
    commands.spawn(PbrBundle {
        mesh: meshes.add(
            UVSphere {
                radius: 0.5,
                ..default()
            }
            .into(),
        ),
        material: materials.add(StandardMaterial {
            perceptual_roughness: 0.089,
            metallic: 1.,
            ..default()
        }),
        transform: Transform::from_xyz(-1.25, 0.5, 0.),
        ..default()
    });

    // middle
    commands.spawn(PbrBundle {
        mesh: meshes.add(
            UVSphere {
                radius: 0.5,
                ..default()
            }
            .into(),
        ),
        material: materials.add(StandardMaterial {
            perceptual_roughness: 0.5,
            metallic: 1.,
            ..default()
        }),
        transform: Transform::from_xyz(0., 0.5, 0.),
        ..default()
    });

    // right
    commands.spawn(PbrBundle {
        mesh: meshes.add(
            UVSphere {
                radius: 0.5,
                ..default()
            }
            .into(),
        ),
        material: materials.add(StandardMaterial {
            perceptual_roughness: 1.,
            metallic: 1.,
            ..default()
        }),
        transform: Transform::from_xyz(1.25, 0.5, 0.),
        ..default()
    });

    commands.spawn(PbrBundle {
        mesh: meshes.add(Plane::from_size(5.).into()),
        material: materials.add(StandardMaterial::default()),
        ..default()
    });

    commands.spawn(DirectionalLightBundle {
        directional_light: DirectionalLight {
            illuminance: 20000.,
            shadows_enabled: true,
            ..default()
        },
        transform: Transform::default().looking_to(Vec3::new(-1., -1., -1.), Vec3::Y),
        ..default()
    });
}

Result:

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