Fix atmosphere space view for LUT rendering

[mate-h]

Objective

Since introducing spherical coordinate systems and space views for Bevy's atmosphere in PR #20766, the LUT-based rendering had a remaining bug: when tilting the camera and viewing Earth from space, the lit/dark terminator rotated with the view instead of staying fixed. Raymarched rendering was correct, only the LUT path was affected. This PR fixes that by using an atmosphere frame that keeps the terminator stable while still concentrating texel density toward the horizon as in the Hillaire paper.

This is what the bug reproduction looks like on main:

Screen.Recording.2026-02-12.at.11.45.31.PM.mov

With this change, the atmosphere rendering from space is officially supported using the LUT based method. That can be taken advantage of in lower end devices, or on a tight performance budget.

Solution

• Compute the atmosphere frame with local up for zenith and a world-fixed azimuth
• Use the atmosphere transform for both LUT generation and sampling via direction_world_to_atmosphere, effectively reverting this code block to the previous state before PR Raymarched rendering for atmosphere and spherical coordinates #20766
• Raymarch the sky view LUT from the actual camera position.

Testing

• Ran the atmosphere example by increasing the scene's scale

AtmosphereSettings {
    scene_units_to_m: 10e4,
    aerial_view_lut_max_distance: 3.2e4 * 128.0,
    ..default()
},

---

Showcase

new LUT based rendering:

raymarched rendering for reference "ground truth":