Atmosphere release notes (#2087)

Co-authored-by: Alice Cecile <[email protected]>
Co-authored-by: JMS55 <[email protected]>

Author: 3 people

content/news/2025-XX-XX-bevy-0.16/atmosphere-showcase.mp4

@@ -1,4 +1,32 @@
 <!-- Procedural atmospheric scattering -->
 <!-- https://github.com/bevyengine/bevy/pull/16314 -->
+Bevy 0.16 introduces procedural atmospheric scattering, a customizable system for simulating sunsets, sunrises, and dynamic day/night cycles in real time.
+
+Once it's enabled, the default Bevy skybox is overlaid with one that updates in real-time based on the directional lights in the scene, and the default distance fog is replaced with one that takes into account directional lights and the other atmosphere parameters. Distant objects will fade to blue on a clear day, and will be tinged orange and pink at sunset! Also, because the atmosphere is composited on *top* of the skybox, creating a nighttime starscape is easy--just spawn the skybox and it'll naturally fade away as the sky grows brighter at dawn.
+
+There's some current limitations to be aware of, though: the atmosphere currently doesn't affect the `EnvironmentMapLight` or the direct lighting from directional lights on surfaces, so reflections might not be fully accurate. We're also working on integrating atmospheric scattering with volumetric fog--see below for our ambitious plans :)
+
+```rs
+commands.spawn((
+    Camera3d::default(),
+    // Just add the new Atmosphere component. As with most PBR techniques, it's *correct*, but can take some tweaking to look its best.
+    // The included example at `examples/3d/atmosphere.rs` includes some recommendations for lighting and camera settings.
+    //
+    // All of the atmosphere parameters can also be customized: for example, a high desert sky might exhibit less Mie scattering due to the lack of humidity.
+    // They're not all easy or intuitive to tweak right now, but we're working on adding some nice utilities for this!
+    Atmosphere::EARTH,
+));
+
+// the atmosphere will consider all directional lights in the scene as "suns"
+commands.spawn(DirectionalLight::default());
+```
+
+Because of a number of optimizations described in Sébastien Hillaire's [EGSR 2020 paper], our implementation is super fast, and should work great even on mobile devices and WebGPU. The secret sauce is that because the atmosphere is mostly symmetric, we can precalculate most of the ray marching inner loop ahead of time.
+
+<video controls loop aria-label="A showcase of simulated sunrises and sunsets made in Bevy"><source src="atmosphere-showcase.mp4" type="video/mp4"/></video>
+Credit to `@aevyrie` for their amazing [atmosphere showcase]! It uses a fancy custom exposure curve to accentuate the near-dusk colors.
+
+[atmosphere showcase]: https://github.com/aevyrie/bevy/tree/atmosphere_showcase
+[EGSR 2020 paper]: https://sebh.github.io/publications/egsr2020.pdf
 
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