Change atmospheric units to meters

crates/bevy_pbr/src/atmosphere/aerial_view_lut.wgsl

@@ -39,7 +39,7 @@ fn main(@builtin(global_invocation_id) idx: vec3<u32>) {
         for (var step_i: i32 = i32(settings.aerial_view_lut_samples - 1); step_i >= 0; step_i--) {
             let sample_depth = depth_at_sample(slice_i, step_i);
             //view_dir.w is the cosine of the angle between the view vector and the camera forward vector, used to correct the step length.
-            let t_i = -depth_ndc_to_view_z(sample_depth) / ray_dir.w * settings.scene_units_to_km;
+            let t_i = -depth_ndc_to_view_z(sample_depth) / ray_dir.w * settings.scene_units_to_m;
             let dt = (t_i - prev_t);
             prev_t = t_i;
 

crates/bevy_pbr/src/atmosphere/functions.wgsl

@@ -257,9 +257,9 @@ fn max_atmosphere_distance(r: f32, mu: f32) -> f32 {
     return mix(t_top, t_bottom, f32(hits));
 }
 
-/// Assuming y=0 is the planet ground, returns the view radius in kilometers
+/// Assuming y=0 is the planet ground, returns the view radius in meters
 fn view_radius() -> f32 {
-    return view.world_position.y * settings.scene_units_to_km + atmosphere.bottom_radius;
+    return view.world_position.y * settings.scene_units_to_m + atmosphere.bottom_radius;
 }
 
 // We assume the `up` vector at the view position is the y axis, since the world is locally flat/level.

crates/bevy_pbr/src/atmosphere/mod.rs

@@ -232,24 +232,18 @@ impl Plugin for AtmospherePlugin {
 /// participating in Rayleigh and Mie scattering falls off roughly exponentially
 /// from the planet's surface, ozone only exists in a band centered at a fairly
 /// high altitude.
-///
-/// Note that all units are in kilometers. This is to combat precision issues,
-/// since integrating very small atmospheric densities over long distances
-/// might otherwise cause problems. [`AtmosphereSettings`] has a field to set
-/// the conversion factor from scene units to km, which by default assumes that
-/// the scene units are meters.
 #[derive(Clone, Component, Reflect, ShaderType)]
 #[require(AtmosphereSettings)]
 pub struct Atmosphere {
     /// Radius of the planet
     ///
-    /// units: km
+    /// units: m
     pub bottom_radius: f32,
 
     /// Radius at which we consider the atmosphere to 'end' for our
     /// calculations (from center of planet)
     ///
-    /// units: km
+    /// units: m
     pub top_radius: f32,
 
     /// An approximation of the average albedo (or color, roughly) of the
@@ -259,37 +253,37 @@ pub struct Atmosphere {
     pub ground_albedo: Vec3,
 
     /// The rate of falloff of rayleigh particulate with respect to altitude:
-    /// optical density = exp(-rayleigh_density_exp_scale * altitude).
+    /// optical density = exp(-rayleigh_density_exp_scale * altitude in meters).
     ///
     /// THIS VALUE MUST BE POSITIVE
     ///
     /// units: N/A
     pub rayleigh_density_exp_scale: f32,
 
-    /// The scattering optical density of rayleigh particulare, or how
-    /// much light it scatters per kilometer
+    /// The scattering optical density of rayleigh particulate, or how
+    /// much light it scatters per meter
     ///
-    /// units: km^-1
+    /// units: m^-1
     pub rayleigh_scattering: Vec3,
 
     /// The rate of falloff of mie particulate with respect to altitude:
-    /// optical density = exp(-mie_density_exp_scale * altitude)
+    /// optical density = exp(-mie_density_exp_scale * altitude in meters)
     ///
     /// THIS VALUE MUST BE POSITIVE
     ///
     /// units: N/A
     pub mie_density_exp_scale: f32,
 
     /// The scattering optical density of mie particular, or how much light
-    /// it scatters per kilometer.
+    /// it scatters per meter.
     ///
-    /// units: km^-1
+    /// units: m^-1
     pub mie_scattering: f32,
 
     /// The absorbing optical density of mie particulate, or how much light
-    /// it absorbs per kilometer.
+    /// it absorbs per meter.
     ///
-    /// units: km^-1
+    /// units: m^-1
     pub mie_absorption: f32,
 
     /// The "asymmetry" of mie scattering, or how much light tends to scatter
@@ -301,35 +295,35 @@ pub struct Atmosphere {
 
     /// The altitude at which the ozone layer is centered.
     ///
-    /// units: km
+    /// units: m
     pub ozone_layer_altitude: f32,
 
     /// The width of the ozone layer
     ///
-    /// units: km
+    /// units: m
     pub ozone_layer_width: f32,
 
     /// The optical density of ozone, or how much of each wavelength of
     /// light it absorbs per kilometer.
     ///
-    /// units: km^-1
+    /// units: m^-1
     pub ozone_absorption: Vec3,
 }
 
 impl Atmosphere {
     pub const EARTH: Atmosphere = Atmosphere {
-        bottom_radius: 6360.0,
-        top_radius: 6460.0,
+        bottom_radius: 6360_000.0,
+        top_radius: 6460_000.0,
         ground_albedo: Vec3::splat(0.3),
-        rayleigh_density_exp_scale: 1.0 / 8.0,
-        rayleigh_scattering: Vec3::new(0.005802, 0.013558, 0.033100),
-        mie_density_exp_scale: 1.0 / 1.2,
-        mie_scattering: 0.003996,
-        mie_absorption: 0.0004440,
+        rayleigh_density_exp_scale: 1.0 / 8000.0,
+        rayleigh_scattering: Vec3::new(5.802e-6, 13.558e-6, 33.100e-6),
+        mie_density_exp_scale: 1.0 / 1200.0,
+        mie_scattering: 3.996e-6,
+        mie_absorption: 0.444e-6,
         mie_asymmetry: 0.8,
-        ozone_layer_altitude: 25.0,
-        ozone_layer_width: 30.0,
-        ozone_absorption: Vec3::new(0.000650, 0.001881, 0.000085),
+        ozone_layer_altitude: 25000.0,
+        ozone_layer_width: 30000.0,
+        ozone_absorption: Vec3::new(0.650e-6, 1.881e-6, 0.085e-6),
     };
 
     pub fn with_density_multiplier(&self, mult: f32) -> Self {
@@ -412,9 +406,9 @@ pub struct AtmosphereSettings {
     /// of the aerial-view LUT.
     pub aerial_view_lut_samples: u32,
 
-    /// A conversion factor between scene units and kilometers, used to
+    /// A conversion factor between scene units and meters, used to
     /// combat floating-point precision issues.
-    pub scene_units_to_km: f32,
+    pub scene_units_to_m: f32,
 }
 
 impl Default for AtmosphereSettings {
@@ -429,7 +423,7 @@ impl Default for AtmosphereSettings {
             sky_view_lut_samples: 16,
             aerial_view_lut_size: UVec3::new(32, 32, 32),
             aerial_view_lut_samples: 10,
-            scene_units_to_km: 1.0e-3,
+            scene_units_to_m: 1.0,
         }
     }
 }

crates/bevy_pbr/src/atmosphere/types.wgsl

@@ -32,7 +32,7 @@ struct AtmosphereSettings {
     multiscattering_lut_samples: u32,
     sky_view_lut_samples: u32,
     aerial_view_lut_samples: u32,
-    scene_units_to_km: f32,
+    scene_units_to_m: f32,
 }
 
 

examples/3d/atmosphere.rs

@@ -7,6 +7,7 @@ use bevy::{
     pbr::{Atmosphere, AtmosphereSettings, CascadeShadowConfigBuilder},
     prelude::*,
 };
+use bevy_render::camera::Exposure;
 use light_consts::lux;
 
 fn main() {
@@ -20,6 +21,7 @@ fn main() {
 fn setup_camera_fog(mut commands: Commands) {
     commands.spawn((
         Camera3d::default(),
+        Exposure { ev100: 11.0 },
         Camera {
             hdr: true,
             ..default()
@@ -29,7 +31,7 @@ fn setup_camera_fog(mut commands: Commands) {
         Atmosphere::EARTH,
         Bloom::NATURAL,
         AtmosphereSettings {
-            scene_units_to_km: 1.0,
+            scene_units_to_m: 1e+3,
             ..Default::default()
         },
     ));