light: add SunDisk::MARS preset for Mars atmosphere

crates/bevy_light/src/directional_light.rs

@@ -257,8 +257,9 @@ pub fn update_directional_light_frusta(
 /// Requires a `bevy::pbr::Atmosphere` component on a [`Camera3d`](bevy_camera::Camera3d) to have any effect.
 ///
 /// By default, the atmosphere is rendered with [`SunDisk::EARTH`], which approximates the
-/// apparent size and brightness of the Sun as seen from Earth. You can also disable the sun
-/// disk entirely with [`SunDisk::OFF`].
+/// apparent size and brightness of the Sun as seen from Earth. Use [`SunDisk::MARS`] for the
+/// smaller apparent sun size from Mars. You can also disable the sun disk entirely
+/// with [`SunDisk::OFF`].
 ///
 /// In order to cause the sun to "glow" and light up the surrounding sky, enable bloom
 /// in your post-processing pipeline by adding a `Bloom` component to your camera.
@@ -284,6 +285,15 @@ impl SunDisk {
         intensity: 1.0,
     };
 
+    /// Mars-like parameters for the sun disk.
+    ///
+    /// Uses the mean apparent size (~21 arcminutes) of the Sun from Mars
+    /// at ~1.52 AU distance with default intensity.
+    pub const MARS: SunDisk = SunDisk {
+        angular_size: 0.00615,
+        intensity: 1.0,
+    };
+
     /// No visible sun disk.
     ///
     /// Keeps scattering and directional light illumination, but hides the disk itself.

examples/3d/atmosphere.rs

@@ -15,7 +15,7 @@ use bevy::{
     input::keyboard::KeyCode,
     light::{
         atmosphere::ScatteringMedium, light_consts::lux, Atmosphere, AtmosphereEnvironmentMapLight,
-        FogVolume, VolumetricFog, VolumetricLight,
+        FogVolume, SunDisk, VolumetricFog, VolumetricLight,
     },
     pbr::{
         AtmosphereMode, AtmosphereSettings, DefaultOpaqueRendererMethod, ExtendedMaterial,
@@ -72,6 +72,7 @@ fn atmosphere_controls(
     keyboard_input: Res<ButtonInput<KeyCode>>,
     mut planet_atmosphere: Query<(&mut Atmosphere, &mut GlobalTransform)>,
     mut camera_settings: Query<&mut AtmosphereSettings, With<Camera3d>>,
+    mut sun_disks: Query<&mut SunDisk, With<DirectionalLight>>,
     atmosphere_presets: Res<AtmospherePresets>,
     mut game_state: ResMut<GameState>,
     mut camera_exposure: Query<&mut Exposure, With<Camera3d>>,
@@ -81,16 +82,22 @@ fn atmosphere_controls(
         for (mut atmosphere, mut transform) in &mut planet_atmosphere {
             *atmosphere = Atmosphere::earth(atmosphere_presets.earth.clone());
             *transform = GlobalTransform::from_translation(-Vec3::Y * atmosphere.inner_radius);
-            println!("Switched to Earth atmosphere");
         }
+        for mut sun_disk in &mut sun_disks {
+            sun_disk.angular_size = SunDisk::EARTH.angular_size;
+        }
+        println!("Switched to Earth atmosphere");
     }
 
     if keyboard_input.just_pressed(KeyCode::Digit4) {
         for (mut atmosphere, mut transform) in &mut planet_atmosphere {
             *atmosphere = Atmosphere::mars(atmosphere_presets.mars.clone());
             *transform = GlobalTransform::from_translation(-Vec3::Y * atmosphere.inner_radius);
-            println!("Switched to Mars atmosphere");
         }
+        for mut sun_disk in &mut sun_disks {
+            sun_disk.angular_size = SunDisk::MARS.angular_size;
+        }
+        println!("Switched to Mars atmosphere");
     }
 
     if keyboard_input.just_pressed(KeyCode::Digit1) {
@@ -229,6 +236,7 @@ fn setup_terrain_scene(
         },
         Transform::from_xyz(1.0, 0.4, 0.0).looking_at(Vec3::ZERO, Vec3::Y),
         VolumetricLight,
+        SunDisk::EARTH,
     ));
 
     // spawn the fog volume