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//! Demonstrates how to use transparency in 3D.
//! Shows the effects of different blend modes.
//! The `fade_transparency` system smoothly changes the transparency over time.
use bevy::prelude::*;
fn main() {
App::new()
.insert_resource(Msaa::default())
.add_plugins(DefaultPlugins)
.add_systems(Startup, setup)
.add_systems(Update, fade_transparency)
.run();
}
fn setup(
mut commands: Commands,
mut meshes: ResMut<Assets<Mesh>>,
mut materials: ResMut<Assets<StandardMaterial>>,
) {
// Opaque plane, uses `alpha_mode: Opaque` by default
commands.spawn(PbrBundle {
mesh: meshes.add(Plane3d::default().mesh().size(6.0, 6.0)),
material: materials.add(Color::srgb(0.3, 0.5, 0.3)),
..default()
});
// Transparent sphere, uses `alpha_mode: Mask(f32)`
commands.spawn(PbrBundle {
mesh: meshes.add(Sphere::new(0.5).mesh().ico(3).unwrap()),
material: materials.add(StandardMaterial {
// Alpha channel of the color controls transparency.
// We set it to 0.0 here, because it will be changed over time in the
// `fade_transparency` function.
// Note that the transparency has no effect on the objects shadow.
base_color: Color::srgba(0.2, 0.7, 0.1, 0.0),
// Mask sets a cutoff for transparency. Alpha values below are fully transparent,
// alpha values above are fully opaque.
alpha_mode: AlphaMode::Mask(0.5),
..default()
}),
transform: Transform::from_xyz(1.0, 0.5, -1.5),
..default()
});
// Transparent unlit sphere, uses `alpha_mode: Mask(f32)`
commands.spawn(PbrBundle {
mesh: meshes.add(Sphere::new(0.5).mesh().ico(3).unwrap()),
material: materials.add(StandardMaterial {
base_color: Color::srgba(0.2, 0.7, 0.1, 0.0),
alpha_mode: AlphaMode::Mask(0.5),
unlit: true,
..default()
}),
transform: Transform::from_xyz(-1.0, 0.5, -1.5),
..default()
});
// Transparent cube, uses `alpha_mode: Blend`
commands.spawn(PbrBundle {
mesh: meshes.add(Cuboid::default()),
// Notice how there is no need to set the `alpha_mode` explicitly here.
// When converting a color to a material using `into()`, the alpha mode is
// automatically set to `Blend` if the alpha channel is anything lower than 1.0.
material: materials.add(Color::srgba(0.5, 0.5, 1.0, 0.0)),
transform: Transform::from_xyz(0.0, 0.5, 0.0),
..default()
});
// Transparent cube, uses `alpha_mode: AlphaToCoverage`
commands.spawn(PbrBundle {
mesh: meshes.add(Cuboid::default()),
material: materials.add(StandardMaterial {
base_color: Color::srgba(0.5, 1.0, 0.5, 0.0),
alpha_mode: AlphaMode::AlphaToCoverage,
..default()
}),
transform: Transform::from_xyz(-1.5, 0.5, 0.0),
..default()
});
// Opaque sphere
commands.spawn(PbrBundle {
mesh: meshes.add(Sphere::new(0.5).mesh().ico(3).unwrap()),
material: materials.add(Color::srgb(0.7, 0.2, 0.1)),
transform: Transform::from_xyz(0.0, 0.5, -1.5),
..default()
});
// Light
commands.spawn(PointLightBundle {
point_light: PointLight {
shadows_enabled: true,
..default()
},
transform: Transform::from_xyz(4.0, 8.0, 4.0),
..default()
});
// Camera
commands.spawn(Camera3dBundle {
transform: Transform::from_xyz(-2.0, 3.0, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
..default()
});
}
/// Fades the alpha channel of all materials between 0 and 1 over time.
/// Each blend mode responds differently to this:
/// - [`Opaque`](AlphaMode::Opaque): Ignores alpha channel altogether, these materials stay completely opaque.
/// - [`Mask(f32)`](AlphaMode::Mask): Object appears when the alpha value goes above the mask's threshold, disappears
/// when the alpha value goes back below the threshold.
/// - [`Blend`](AlphaMode::Blend): Object fades in and out smoothly.
/// - [`AlphaToCoverage`](AlphaMode::AlphaToCoverage): Object fades in and out
/// in steps corresponding to the number of multisample antialiasing (MSAA)
/// samples in use. For example, assuming 8xMSAA, the object will be
/// completely opaque, then will be 7/8 opaque (1/8 transparent), then will be
/// 6/8 opaque, then 5/8, etc.
pub fn fade_transparency(time: Res<Time>, mut materials: ResMut<Assets<StandardMaterial>>) {
let alpha = (time.elapsed_seconds().sin() / 2.0) + 0.5;
for (_, material) in materials.iter_mut() {
material.base_color.set_alpha(alpha);
}
}