# Objective
- There is a flaw in the implementation of `FogVolume`'s
`density_texture_offset` from #14868. Because of the way I am wrapping
the UVW coordinates in the volumetric fog shader, a seam is visible when
the 3d texture is wrapping around from one side to the other:
## Solution
- This PR fixes the issue by removing the wrapping from the shader and
instead leaving it to the user to configure the 3d noise texture to use
`ImageAddressMode::Repeat` if they want it to repeat. Using
`ImageAddressMode::Repeat` is the proper solution to avoid the obvious
seam:
- The sampler cannot be implicitly configured to use
`ImageAddressMode::Repeat` because that's not always desirable. For
example, the `fog_volumes` example wouldn't work properly because the
texture from the edges of the volume would overflow to the other sides,
which would be bad in this instance (but it's good in the case of the
`scrolling_fog` example). So leaving it to the user to decide on their
own whether they want the density texture to repeat seems to be the best
solution.
## Testing
- The `scrolling_fog` example still looks the same, it was just changed
to explicitly declare that the density texture should be repeating when
loading the asset. The `fog_volumes` example is unaffected.
<details>
<summary>Minimal reproduction example on current main</summary>
<pre>
use bevy::core_pipeline::experimental::taa::{TemporalAntiAliasBundle,
TemporalAntiAliasPlugin};
use bevy::pbr::{FogVolume, VolumetricFogSettings, VolumetricLight};
use bevy::prelude::*;<br>
fn main() {
App::new()
.add_plugins((DefaultPlugins, TemporalAntiAliasPlugin))
.add_systems(Startup, setup)
.run();
}<br>
fn setup(mut commands: Commands, assets: Res<AssetServer>) {
commands.spawn((
Camera3dBundle {
transform: Transform::from_xyz(3.5, -1.0, 0.4)
.looking_at(Vec3::new(0.0, 0.0, 0.4), Vec3::Y),
msaa: Msaa::Off,
..default()
},
TemporalAntiAliasBundle::default(),
VolumetricFogSettings {
ambient_intensity: 0.0,
jitter: 0.5,
..default()
},
));<br>
commands.spawn((
DirectionalLightBundle {
transform: Transform::from_xyz(-6.0, 5.0, -9.0)
.looking_at(Vec3::new(0.0, 0.0, 0.0), Vec3::Y),
directional_light: DirectionalLight {
illuminance: 32_000.0,
shadows_enabled: true,
..default()
},
..default()
},
VolumetricLight,
));<br>
commands.spawn((
SpatialBundle {
visibility: Visibility::Visible,
transform: Transform::from_xyz(0.0, 0.0,
0.0).with_scale(Vec3::splat(3.0)),
..default()
},
FogVolume {
density_texture: Some(assets.load("volumes/fog_noise.ktx2")),
density_texture_offset: Vec3::new(0.0, 0.0, 0.4),
scattering: 1.0,
..default()
},
));
}
</pre>
</details>
# 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
