ClearColor and Sprite same value yields different color

[RobotSnowOtter]

Bevy version

Bevy 0.6.1

Operating system & version

Pop!_OS 21.10 x86_64

What you did

Set a sprite and the background to the same rgb value

use bevy::prelude::*;

const BG_COLOR: Color = Color::rgb(0.16, 0.16, 0.16);

fn main() {
    App::new()
        .insert_resource(ClearColor(BG_COLOR))
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup)
        .run();
}

fn setup(mut commands: Commands) {
    commands.spawn_bundle(OrthographicCameraBundle::new_2d());

    commands.spawn_bundle(SpriteBundle {
        sprite: Sprite {
            color: BG_COLOR,
            custom_size: Some(Vec2::new(50.0, 50.0)),
            ..Default::default()
        },
        ..Default::default()
    });
}

What you expected to happen

The rectangle sprite should be indistinguishable from the background.
Only one color should be visible.

What actually happened

The sprite (center) renders slightly darker than the background.

[alice-i-cecile]

Good find. Thanks for the excellent issue and report. Under the hood, I bet this has something to do with linear vs sRGB colors.

[mockersf]

Issue is that Color in wgpu is using f64, but we're using f32 then u8, and the difference is in the rounding

[CptPotato]

Issue is that Color in wgpu is using f64, but we're using f32 then u8, and the difference is in the rounding

Is it confirmed that this is a rounding issue? I would have expected the rgb value to be off by one in that case but the values are 38 vs 41 in the screenshot.

Even considering f32 to u8 conversion, you'd expect 0.16 to be 40.8 so either 40 or 41 which matches the background color. Compared to that the sprite is too dark. Though, maybe there are other things at play, too (desktop composition / color management / etc).

[mockersf]

I can reproduce the issue, and it is fixed by #4357, so I'm fairly certain it's a rounding issue somewhere

[CptPotato]

Didn't see the PR, thanks for elaborating. I tried it with a few different colors and they all seem to match up.

Though, I would prefer a different fix if I'm honest. With #4357 I'm not able to set accurate clear colors using Color::rgb_u8(). Anything below (13, 13, 13) is black for example.

I guess it's because the quantization to u8 is done using linear color, not srgb which makes it lose a ton of accuracy for darker colors.

[cart]

I'm relatively certain that this is from our sprite rendering code, which converts the input color to u8s and stores them in a single u32 vertex attribute. (see vertex_color in sprite.wgsl).

If anything this is a "bug" there. One fix would be to pass each float in individually as a vec4 vertex attribute, which would increase the cost of rendering (iirc this "compression" yielded non-trivial performance wins when rendering many sprites).

[CooCooCaCha]

IMO the most important thing is accurate color. As a user I would expect the colors in my sprite to match my drawing program.

[mockersf]

If anything this is a "bug" there

I'm not sure this is so much a bug as a "known limitation" that should be documented... This would only be visible when using the sprite color instead of an image, which doesn't feel like the main feature.
If a user want more accurate color, it is possible with the Mesh2dBundle instead of the SpriteBundle

[cart]

I'm not sure this is so much a bug as a "known limitation" that should be documented... This would only be visible when using the sprite color instead of an image, which doesn't feel like the main feature.

"wrong color" is a bug imo (but i agree that this is a matter of perspective). these things should "just work" in a way that is compatible across features. if an artist cant easily say "i want this sprite to be the same color as the background", thats on us to fix i think (and probably takes precedence over optimization, at least for defaults)

[mockersf]

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<ColorMaterial>>,
) {
    commands.spawn_bundle(OrthographicCameraBundle::new_2d());

    commands.spawn_bundle(SpriteBundle {
        transform: Transform::from_xyz(50.0, 0.0, 0.0),
        sprite: Sprite {
            color: BG_COLOR,
            custom_size: Some(Vec2::new(100.0, 100.0)),
            ..Default::default()
        },
        ..Default::default()
    });

    commands.spawn_bundle(MaterialMesh2dBundle {
        mesh: meshes.add(Mesh::from(shape::Quad::default())).into(),
        transform: Transform::default()
            .with_scale(Vec3::splat(100.0))
            .with_translation(Vec3::new(-50.0, 0.0, 0.0)),
        material: materials.add(ColorMaterial::from(BG_COLOR)),
        ..default()
    });
}

the MaterialMesh2dBundle will have the expected color, SpriteBundle won't