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Allow fog density texture to be scrolled over time with an offset (#14868)
# Objective - The goal of this PR is to make it possible to move the density texture of a `FogVolume` over time in order to create dynamic effects like fog moving in the wind. - You could theoretically move the `FogVolume` itself, but this is not ideal, because the `FogVolume` AABB would eventually leave the area. If you want an area to remain foggy while also creating the impression that the fog is moving in the wind, a scrolling density texture is a better solution. ## Solution - The PR adds a `density_texture_offset` field to the `FogVolume` component. This offset is in the UVW coordinates of the density texture, meaning that a value of `(0.5, 0.0, 0.0)` moves the 3d texture by half along the x-axis. - Values above 1.0 are wrapped, a 1.5 offset is the same as a 0.5 offset. This makes it so that the density texture wraps around on the other side, meaning that a repeating 3d noise texture can seamlessly scroll forever. It also makes it easy to move the density texture over time by simply increasing the offset every frame. ## Testing - A `scrolling_fog` example has been added to demonstrate the feature. It uses the offset to scroll a repeating 3d noise density texture to create the impression of fog moving in the wind. - The camera is looking at a pillar with the sun peaking behind it. This highlights the effect the changing density has on the volumetric lighting interactions. - Temporal anti-aliasing combined with the `jitter` option of `VolumetricFogSettings` is used to improve the quality of the effect. --- ## Showcase https://github.com/user-attachments/assets/3aa50ebd-771c-4c99-ab5d-255c0c3be1a8
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7 changed files with 151 additions and 1 deletions
11
Cargo.toml
11
Cargo.toml
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@ -3330,6 +3330,17 @@ description = "Demonstrates fog volumes"
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category = "3D Rendering"
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wasm = false
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[[example]]
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name = "scrolling_fog"
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path = "examples/3d/scrolling_fog.rs"
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doc-scrape-examples = true
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[package.metadata.example.scrolling_fog]
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name = "Scrolling fog"
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description = "Demonstrates how to create the effect of fog moving in the wind"
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category = "3D Rendering"
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wasm = false
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[[example]]
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name = "physics_in_fixed_timestep"
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path = "examples/movement/physics_in_fixed_timestep.rs"
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BIN
assets/volumes/fog_noise.ktx2
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BIN
assets/volumes/fog_noise.ktx2
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Binary file not shown.
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@ -150,8 +150,20 @@ pub struct FogVolume {
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/// The default value is 0.1.
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pub density_factor: f32,
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/// Optional 3D voxel density texture for the fog.
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pub density_texture: Option<Handle<Image>>,
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/// Configurable offset of the density texture in UVW coordinates. Values 1.0 or higher
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/// will be wrapped into the (0.0..1.0) range.
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///
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/// This can be used to scroll a repeating density texture in a direction over time
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/// to create effects like fog moving in the wind.
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///
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/// Has no effect when no density texture is present.
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///
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/// The default value is (0, 0, 0).
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pub density_texture_offset: Vec3,
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/// The absorption coefficient, which measures what fraction of light is
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/// absorbed by the fog at each step.
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///
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@ -268,6 +280,7 @@ impl Default for FogVolume {
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scattering: 0.3,
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density_factor: 0.1,
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density_texture: None,
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density_texture_offset: Vec3::ZERO,
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scattering_asymmetry: 0.5,
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fog_color: Color::WHITE,
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light_tint: Color::WHITE,
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@ -183,6 +183,7 @@ pub struct VolumetricFogUniform {
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absorption: f32,
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scattering: f32,
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density: f32,
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density_texture_offset: Vec3,
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scattering_asymmetry: f32,
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light_intensity: f32,
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jitter_strength: f32,
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@ -727,6 +728,7 @@ pub fn prepare_volumetric_fog_uniforms(
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absorption: fog_volume.absorption,
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scattering: fog_volume.scattering,
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density: fog_volume.density_factor,
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density_texture_offset: fog_volume.density_texture_offset,
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scattering_asymmetry: fog_volume.scattering_asymmetry,
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light_intensity: fog_volume.light_intensity,
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jitter_strength: volumetric_fog_settings.jitter,
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@ -43,6 +43,7 @@ struct VolumetricFog {
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absorption: f32,
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scattering: f32,
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density_factor: f32,
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density_texture_offset: vec3<f32>,
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scattering_asymmetry: f32,
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light_intensity: f32,
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jitter_strength: f32,
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@ -101,6 +102,7 @@ fn fragment(@builtin(position) position: vec4<f32>) -> @location(0) vec4<f32> {
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let absorption = volumetric_fog.absorption;
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let scattering = volumetric_fog.scattering;
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let density_factor = volumetric_fog.density_factor;
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let density_texture_offset = volumetric_fog.density_texture_offset;
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let light_tint = volumetric_fog.light_tint;
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let light_intensity = volumetric_fog.light_intensity;
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let jitter_strength = volumetric_fog.jitter_strength;
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@ -236,7 +238,11 @@ fn fragment(@builtin(position) position: vec4<f32>) -> @location(0) vec4<f32> {
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// case.
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let P_uvw = Ro_uvw + Rd_step_uvw * f32(step);
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if (all(P_uvw >= vec3(0.0)) && all(P_uvw <= vec3(1.0))) {
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density *= textureSample(density_texture, density_sampler, P_uvw).r;
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// Add density texture offset and wrap values exceeding the (0, 0, 0) to (1, 1, 1) range.
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var uvw = P_uvw + density_texture_offset;
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uvw -= floor(uvw);
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density *= textureSample(density_texture, density_sampler, uvw).r;
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} else {
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density = 0.0;
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}
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117
examples/3d/scrolling_fog.rs
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117
examples/3d/scrolling_fog.rs
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@ -0,0 +1,117 @@
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//! Showcases a `FogVolume`'s density texture being scrolled over time to create
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//! the effect of fog moving in the wind.
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//!
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//! The density texture is a repeating 3d noise texture and the `density_texture_offset`
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//! is moved every frame to achieve this.
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//!
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//! The example also utilizes the jitter option of `VolumetricFogSettings` in tandem
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//! with temporal anti-aliasing to improve the visual quality of the effect.
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//!
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//! The camera is looking at a pillar with the sun peaking behind it. The light
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//! interactions change based on the density of the fog.
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use bevy::core_pipeline::bloom::BloomSettings;
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use bevy::core_pipeline::experimental::taa::{TemporalAntiAliasBundle, TemporalAntiAliasPlugin};
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use bevy::pbr::{DirectionalLightShadowMap, FogVolume, VolumetricFogSettings, VolumetricLight};
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use bevy::prelude::*;
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/// Initializes the example.
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fn main() {
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App::new()
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.add_plugins(DefaultPlugins.set(WindowPlugin {
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primary_window: Some(Window {
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title: "Bevy Scrolling Fog".into(),
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..default()
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}),
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..default()
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}))
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.insert_resource(DirectionalLightShadowMap { size: 4096 })
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.add_plugins(TemporalAntiAliasPlugin)
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.add_systems(Startup, setup)
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.add_systems(Update, scroll_fog)
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.run();
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}
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/// Spawns all entities into the scene.
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fn setup(
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mut commands: Commands,
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mut meshes: ResMut<Assets<Mesh>>,
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mut materials: ResMut<Assets<StandardMaterial>>,
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assets: Res<AssetServer>,
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) {
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// Spawn camera with temporal anti-aliasing and a VolumetricFogSettings configuration.
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commands.spawn((
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Camera3dBundle {
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transform: Transform::from_xyz(0.0, 2.0, 0.0)
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.looking_at(Vec3::new(-5.0, 3.5, -6.0), Vec3::Y),
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camera: Camera {
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hdr: true,
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..default()
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},
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msaa: Msaa::Off,
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..default()
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},
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TemporalAntiAliasBundle::default(),
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BloomSettings::default(),
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VolumetricFogSettings {
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ambient_intensity: 0.0,
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jitter: 0.5,
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..default()
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},
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));
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// Spawn a directional light shining at the camera with the VolumetricLight component.
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commands.spawn((
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DirectionalLightBundle {
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transform: Transform::from_xyz(-5.0, 5.0, -7.0)
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.looking_at(Vec3::new(0.0, 0.0, 0.0), Vec3::Y),
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directional_light: DirectionalLight {
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shadows_enabled: true,
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..default()
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},
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..default()
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},
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VolumetricLight,
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));
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// Spawn ground mesh.
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commands.spawn(PbrBundle {
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transform: Transform::from_xyz(0.0, -0.5, 0.0),
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mesh: meshes.add(Cuboid::new(64.0, 1.0, 64.0)),
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material: materials.add(StandardMaterial {
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base_color: Color::BLACK,
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perceptual_roughness: 1.0,
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..default()
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}),
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..default()
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});
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// Spawn pillar standing between the camera and the sun.
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commands.spawn(PbrBundle {
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transform: Transform::from_xyz(-10.0, 4.5, -11.0),
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mesh: meshes.add(Cuboid::new(2.0, 9.0, 2.0)),
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material: materials.add(Color::BLACK),
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..default()
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});
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// Spawn FogVolume with repeating 3d noise density texture.
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commands.spawn((
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SpatialBundle {
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visibility: Visibility::Visible,
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transform: Transform::from_xyz(0.0, 32.0, 0.0).with_scale(Vec3::splat(64.0)),
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..default()
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},
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FogVolume {
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density_texture: Some(assets.load("volumes/fog_noise.ktx2")),
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density_factor: 0.05,
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..default()
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},
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));
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}
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/// Moves fog density texture offset every frame.
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fn scroll_fog(time: Res<Time>, mut query: Query<&mut FogVolume>) {
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for mut fog_volume in query.iter_mut() {
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fog_volume.density_texture_offset += Vec3::new(0.0, 0.0, 0.04) * time.delta_seconds();
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}
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}
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@ -162,6 +162,7 @@ Example | Description
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[Rotate Environment Map](../examples/3d/rotate_environment_map.rs) | Demonstrates how to rotate the skybox and the environment map simultaneously
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[Screen Space Ambient Occlusion](../examples/3d/ssao.rs) | A scene showcasing screen space ambient occlusion
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[Screen Space Reflections](../examples/3d/ssr.rs) | Demonstrates screen space reflections with water ripples
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[Scrolling fog](../examples/3d/scrolling_fog.rs) | Demonstrates how to create the effect of fog moving in the wind
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[Shadow Biases](../examples/3d/shadow_biases.rs) | Demonstrates how shadow biases affect shadows in a 3d scene
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[Shadow Caster and Receiver](../examples/3d/shadow_caster_receiver.rs) | Demonstrates how to prevent meshes from casting/receiving shadows in a 3d scene
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[Skybox](../examples/3d/skybox.rs) | Load a cubemap texture onto a cube like a skybox and cycle through different compressed texture formats.
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