Specular from area lights is disproportionately bright

[DGriffin91]

Bevy version Main https://github.com/bevyengine/bevy/commit/dcb8a13b223fbc9425f7af01b3941dd80a229384, 0.13

This isn't a new issue. Not sure how far it goes back, or if there's exists a previous version without it.

Specular reflections from spot/point area lights are disproportionately bright relative to the diffuse response. This often results in extremely bright specular reflections given sufficiently large area lights.

This image also displays other specular-related issues in bevy that are not relevant to this issue, let's keep this issue focused, please refer to the blender comparison images below.

Test setup: I disabled Tonemapping in both blender and bevy. I visually matched the light brightness using just diffuse. The diffuse falloff in bevy doesn't exactly match blender, but it's close. In blender I'm rendering using Cycles with direct light only (no GI).

I apologize in advance for the amount of comparison images needed. Note that bevy 0 radius is very similar to blender 0 radius across the board, and bevy 1 radius diffuse is similar to blender 1 radius diffuse (though blender wraps around a bit more here). But bevy 1 radius specular is dramatically brighter than blender 1 radius specular.

Bevy 0 radius, diffuse only:

Blender 0 radius, diffuse only:

Bevy 0 radius, specular only:

Blender 0 radius, specular only:

Bevy 0 radius, both specular and diffuse:

Blender 0 radius, both specular and diffuse:

Bevy 1 radius, diffuse only:

Blender 1 radius, diffuse only:

Bevy 1 radius, specular only:

Blender 1 radius, specular only:

Bevy 1 radius, both specular and diffuse:

Blender 1 radius, both specular and diffuse:

Bevy 1 radius, both specular and diffuse, sharp:

Blender 1 radius, both specular and diffuse, sharp:

Blender Test Scene (Blender 4.1): bevy_spec_ref.zip Bevy test scene (Bevy Main https://github.com/bevyengine/bevy/commit/dcb8a13b223fbc9425f7af01b3941dd80a229384):

fn main() {
    App::new()
        .insert_resource(ClearColor(Color::BLACK))
        .insert_resource(AmbientLight::NONE)
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(Update, screenshot_on_spacebar)
        .run();
}
fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    let sphere_mesh = meshes.add(Sphere::new(1.0).mesh().uv(128, 64));
    let surface_material = materials.add(StandardMaterial {
        // Set RGB to 0 to disable diffuse, otherwise use 0.5
        base_color: Color::linear_rgba(0.5, 0.5, 0.5, 1.0),
        // Set reflectance to 0 to disable specular, otherwise use 0.5
        reflectance: 0.5,
        perceptual_roughness: 0.5, // use 0.089 or 0.5
        ..default()
    });
    commands.spawn(PbrBundle {
        mesh: meshes.add(Plane3d::default().mesh().size(100.0, 100.0)),
        material: surface_material.clone(),
        ..default()
    });
    commands.spawn(PbrBundle {
        transform: Transform::from_xyz(-2.5, 1.0, 3.0),
        mesh: sphere_mesh.clone(),
        material: surface_material.clone(),
        ..default()
    });
    commands.spawn(PbrBundle {
        transform: Transform::from_xyz(0.0, 2.5, 3.0),
        mesh: sphere_mesh.clone(),
        material: surface_material.clone(),
        ..default()
    });
    commands.spawn(PointLightBundle {
        point_light: PointLight {
            intensity: 80000.0,
            radius: 1.0,
            ..default()
        },
        transform: Transform::from_xyz(0.0, 1.0, 0.0),
        ..default()
    });
    commands.spawn(Camera3dBundle {
        projection: Projection::Perspective(PerspectiveProjection {
            fov: 45.2f32.to_radians(),
            ..default()
        }),
        tonemapping: Tonemapping::None,
        transform: Transform::from_xyz(0.0, 1.0, 7.0).looking_at(Vec3::ZERO, Vec3::Y),
        ..default()
    });
}
fn screenshot_on_spacebar(
    input: Res<ButtonInput<KeyCode>>,
    main_window: Query<Entity, With<PrimaryWindow>>,
    mut screenshot_manager: ResMut<ScreenshotManager>,
    mut counter: Local<u32>,
) {
    if input.just_pressed(KeyCode::Space) {
        let path = format!("./screenshot-{}.png", *counter);
        *counter += 1;
        screenshot_manager
            .save_screenshot_to_disk(main_window.single(), path)
            .unwrap();
    }
}

[geckoxx]

You mentioned a "Soft Falloff" Settung in Blender in #13318. Is it enabled in the comparison images?

[DGriffin91]

@geckoxx It is not.