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bevy/assets/volumes
Jiří Švejda 510fce9af3
Allow fog density texture to be scrolled over time with an offset ()
# 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
2024-08-22 19:43:14 +00:00
..
bunny.ktx2 Allow volumetric fog to be localized to specific, optionally voxelized, regions. () 2024-07-16 03:14:12 +00:00
fog_noise.ktx2 Allow fog density texture to be scrolled over time with an offset () 2024-08-22 19:43:14 +00:00