Atmosphere occlusion and PBR shading

crates/bevy_pbr/src/atmosphere/bruneton_functions.wgsl

@@ -64,19 +64,19 @@
 // Assuming r between ground and top atmosphere boundary, and mu= cos(zenith_angle)
 // Chosen to increase precision near the ground and to work around a discontinuity at the horizon
 // See Bruneton and Neyret 2008, "Precomputed Atmospheric Scattering" section 4
-fn transmittance_lut_r_mu_to_uv(r: f32, mu: f32) -> vec2<f32> {
+fn transmittance_lut_r_mu_to_uv(atm: Atmosphere, r: f32, mu: f32) -> vec2<f32> {
   // Distance along a horizontal ray from the ground to the top atmosphere boundary
-    let H = sqrt(atmosphere.top_radius * atmosphere.top_radius - atmosphere.bottom_radius * atmosphere.bottom_radius);
+    let H = sqrt(atm.top_radius * atm.top_radius - atm.bottom_radius * atm.bottom_radius);
 
   // Distance from a point at height r to the horizon
   // ignore the case where r <= atmosphere.bottom_radius
-    let rho = sqrt(max(r * r - atmosphere.bottom_radius * atmosphere.bottom_radius, 0.0));
+    let rho = sqrt(max(r * r - atm.bottom_radius * atm.bottom_radius, 0.0));
 
   // Distance from a point at height r to the top atmosphere boundary at zenith angle mu
-    let d = distance_to_top_atmosphere_boundary(r, mu);
+    let d = distance_to_top_atmosphere_boundary(atm, r, mu);
 
   // Minimum and maximum distance to the top atmosphere boundary from a point at height r
-    let d_min = atmosphere.top_radius - r; // length of the ray straight up to the top atmosphere boundary
+    let d_min = atm.top_radius - r; // length of the ray straight up to the top atmosphere boundary
     let d_max = rho + H; // length of the ray to the top atmosphere boundary and grazing the horizon
 
     let u = (d - d_min) / (d_max - d_min);
@@ -121,9 +121,9 @@ fn transmittance_lut_uv_to_r_mu(uv: vec2<f32>) -> vec2<f32> {
 /// Center of sphere, c = [0,0,0]
 /// Radius of sphere, r = atmosphere.top_radius
 /// This function solves the quadratic equation for line-sphere intersection simplified under these assumptions
-fn distance_to_top_atmosphere_boundary(r: f32, mu: f32) -> f32 {
-  // ignore the case where r > atmosphere.top_radius
-    let positive_discriminant = max(r * r * (mu * mu - 1.0) + atmosphere.top_radius * atmosphere.top_radius, 0.0);
+fn distance_to_top_atmosphere_boundary(atm: Atmosphere, r: f32, mu: f32) -> f32 {
+  // ignore the case where r > atm.top_radius
+    let positive_discriminant = max(r * r * (mu * mu - 1.0) + atm.top_radius * atm.top_radius, 0.0);
     return max(-r * mu + sqrt(positive_discriminant), 0.0);
 }
 

crates/bevy_pbr/src/atmosphere/functions.wgsl

@@ -115,7 +115,7 @@ fn sky_view_lut_uv_to_zenith_azimuth(r: f32, uv: vec2<f32>) -> vec2<f32> {
 // LUT SAMPLING
 
 fn sample_transmittance_lut(r: f32, mu: f32) -> vec3<f32> {
-    let uv = transmittance_lut_r_mu_to_uv(r, mu);
+    let uv = transmittance_lut_r_mu_to_uv(atmosphere, r, mu);
     return textureSampleLevel(transmittance_lut, atmosphere_lut_sampler, uv, 0.0).rgb;
 }
 
@@ -256,10 +256,34 @@ fn sample_sun_radiance(ray_dir_ws: vec3<f32>) -> vec3<f32> {
     return sun_radiance;
 }
 
+fn calculate_visible_sun_ratio(atmosphere: Atmosphere, r: f32, mu: f32, sun_angular_size: f32) -> f32 {
+    let bottom_radius = atmosphere.bottom_radius;
+    // Calculate the angle between horizon and sun center
+    // Invert the horizon angle calculation to fix shading direction
+    let horizon_cos = -sqrt(1.0 - (bottom_radius * bottom_radius) / (r * r));
+    let horizon_angle = fast_acos_4(horizon_cos);
+    let sun_zenith_angle = fast_acos_4(mu);
+
+    // If sun is completely above horizon
+    if sun_zenith_angle + sun_angular_size * 0.5 <= horizon_angle {
+        return 1.0;
+    }
+
+    // If sun is completely below horizon
+    if sun_zenith_angle - sun_angular_size * 0.5 >= horizon_angle {
+        return 0.0;
+    }
+
+    // Calculate partial visibility using circular segment area formula
+    let d = (horizon_angle - sun_zenith_angle) / (sun_angular_size * 0.5);
+    let visible_ratio = 0.5 + d * 0.5;
+    return clamp(visible_ratio, 0.0, 1.0);
+}
+
 // TRANSFORM UTILITIES
 
 fn max_atmosphere_distance(r: f32, mu: f32) -> f32 {
-    let t_top = distance_to_top_atmosphere_boundary(r, mu);
+    let t_top = distance_to_top_atmosphere_boundary(atmosphere, r, mu);
     let t_bottom = distance_to_bottom_atmosphere_boundary(r, mu);
     let hits = ray_intersects_ground(r, mu);
     return mix(t_top, t_bottom, f32(hits));

crates/bevy_pbr/src/atmosphere/mod.rs

@@ -77,7 +77,10 @@ use resources::{
 };
 use tracing::warn;
 
-use crate::medium::ScatteringMedium;
+use crate::{
+    medium::ScatteringMedium,
+    resources::{init_atmosphere_buffer, write_atmosphere_buffer},
+};
 
 use self::{
     node::{AtmosphereLutsNode, AtmosphereNode, RenderSkyNode},
@@ -154,7 +157,12 @@ impl Plugin for AtmospherePlugin {
             .init_resource::<SpecializedRenderPipelines<RenderSkyBindGroupLayouts>>()
             .add_systems(
                 RenderStartup,
-                (init_atmosphere_probe_layout, init_atmosphere_probe_pipeline).chain(),
+                (
+                    init_atmosphere_probe_layout,
+                    init_atmosphere_probe_pipeline,
+                    init_atmosphere_buffer,
+                )
+                    .chain(),
             )
             .add_systems(
                 Render,
@@ -171,6 +179,7 @@ impl Plugin for AtmospherePlugin {
                     prepare_atmosphere_probe_bind_groups.in_set(RenderSystems::PrepareBindGroups),
                     prepare_atmosphere_transforms.in_set(RenderSystems::PrepareResources),
                     prepare_atmosphere_bind_groups.in_set(RenderSystems::PrepareBindGroups),
+                    write_atmosphere_buffer.in_set(RenderSystems::PrepareResources),
                 ),
             )
             .add_render_graph_node::<ViewNodeRunner<AtmosphereLutsNode>>(

crates/bevy_pbr/src/atmosphere/resources.rs

@@ -765,3 +765,45 @@ pub(super) fn prepare_atmosphere_bind_groups(
 
     Ok(())
 }
+
+#[derive(ShaderType)]
+#[repr(C)]
+pub(crate) struct AtmosphereData {
+    pub atmosphere: GpuAtmosphere,
+    pub settings: GpuAtmosphereSettings,
+}
+
+pub fn init_atmosphere_buffer(mut commands: Commands) {
+    commands.insert_resource(AtmosphereBuffer {
+        buffer: StorageBuffer::from(AtmosphereData {
+            atmosphere: GpuAtmosphere {
+                ground_albedo: Vec3::ZERO,
+                bottom_radius: 0.0,
+                top_radius: 0.0,
+            },
+            settings: GpuAtmosphereSettings::default(),
+        }),
+    });
+}
+
+#[derive(Resource)]
+pub struct AtmosphereBuffer {
+    pub(crate) buffer: StorageBuffer<AtmosphereData>,
+}
+
+pub(crate) fn write_atmosphere_buffer(
+    device: Res<RenderDevice>,
+    queue: Res<RenderQueue>,
+    atmosphere_entity: Query<(&GpuAtmosphere, &GpuAtmosphereSettings), With<Camera3d>>,
+    mut atmosphere_buffer: ResMut<AtmosphereBuffer>,
+) {
+    let Ok((atmosphere, settings)) = atmosphere_entity.single() else {
+        return;
+    };
+
+    atmosphere_buffer.buffer.set(AtmosphereData {
+        atmosphere: atmosphere.clone(),
+        settings: settings.clone(),
+    });
+    atmosphere_buffer.buffer.write_buffer(&device, &queue);
+}

crates/bevy_pbr/src/atmosphere/types.wgsl

@@ -29,3 +29,8 @@ struct AtmosphereSettings {
 struct AtmosphereTransforms {
     world_from_atmosphere: mat4x4<f32>,
 }
+
+struct AtmosphereData {
+    atmosphere: Atmosphere,
+    settings: AtmosphereSettings,
+}

crates/bevy_pbr/src/deferred/mod.rs

@@ -4,7 +4,10 @@ use crate::{
     ViewLightProbesUniformOffset, ViewScreenSpaceReflectionsUniformOffset,
     TONEMAPPING_LUT_SAMPLER_BINDING_INDEX, TONEMAPPING_LUT_TEXTURE_BINDING_INDEX,
 };
-use crate::{DistanceFog, MeshPipelineKey, ViewFogUniformOffset, ViewLightsUniformOffset};
+use crate::{
+    DistanceFog, ExtractedAtmosphere, MeshPipelineKey, ViewFogUniformOffset,
+    ViewLightsUniformOffset,
+};
 use bevy_app::prelude::*;
 use bevy_asset::{embedded_asset, load_embedded_asset, AssetServer, Handle};
 use bevy_core_pipeline::{
@@ -325,6 +328,9 @@ impl SpecializedRenderPipeline for DeferredLightingLayout {
         if key.contains(MeshPipelineKey::DISTANCE_FOG) {
             shader_defs.push("DISTANCE_FOG".into());
         }
+        if key.contains(MeshPipelineKey::ATMOSPHERE) {
+            shader_defs.push("ATMOSPHERE".into());
+        }
 
         // Always true, since we're in the deferred lighting pipeline
         shader_defs.push("DEFERRED_PREPASS".into());
@@ -452,6 +458,7 @@ pub fn prepare_deferred_lighting_pipelines(
         Has<RenderViewLightProbes<EnvironmentMapLight>>,
         Has<RenderViewLightProbes<IrradianceVolume>>,
         Has<SkipDeferredLighting>,
+        Has<ExtractedAtmosphere>,
     )>,
 ) {
     for (
@@ -465,6 +472,7 @@ pub fn prepare_deferred_lighting_pipelines(
         has_environment_maps,
         has_irradiance_volumes,
         skip_deferred_lighting,
+        has_atmosphere,
     ) in &views
     {
         // If there is no deferred prepass or we want to skip the deferred lighting pass,
@@ -489,6 +497,10 @@ pub fn prepare_deferred_lighting_pipelines(
             view_key |= MeshPipelineKey::MOTION_VECTOR_PREPASS;
         }
 
+        if has_atmosphere {
+            view_key |= MeshPipelineKey::ATMOSPHERE;
+        }
+
         // Always true, since we're in the deferred lighting pipeline
         view_key |= MeshPipelineKey::DEFERRED_PREPASS;
 

crates/bevy_pbr/src/render/mesh.rs

@@ -1,4 +1,7 @@
-use crate::material_bind_groups::{MaterialBindGroupIndex, MaterialBindGroupSlot};
+use crate::{
+    material_bind_groups::{MaterialBindGroupIndex, MaterialBindGroupSlot},
+    resources::write_atmosphere_buffer,
+};
 use bevy_asset::{embedded_asset, load_embedded_asset, AssetId};
 use bevy_camera::{
     primitives::Aabb,
@@ -194,7 +197,8 @@ impl Plugin for MeshRenderPlugin {
                         prepare_mesh_bind_groups.in_set(RenderSystems::PrepareBindGroups),
                         prepare_mesh_view_bind_groups
                             .in_set(RenderSystems::PrepareBindGroups)
-                            .after(prepare_oit_buffers),
+                            .after(prepare_oit_buffers)
+                            .after(write_atmosphere_buffer),
                         no_gpu_preprocessing::clear_batched_cpu_instance_buffers::<MeshPipeline>
                             .in_set(RenderSystems::Cleanup)
                             .after(RenderSystems::Render),
@@ -325,6 +329,7 @@ pub fn check_views_need_specialization(
             Has<RenderViewLightProbes<IrradianceVolume>>,
         ),
         Has<OrderIndependentTransparencySettings>,
+        Has<ExtractedAtmosphere>,
     )>,
     ticks: SystemChangeTick,
 ) {
@@ -342,6 +347,7 @@ pub fn check_views_need_specialization(
         distance_fog,
         (has_environment_maps, has_irradiance_volumes),
         has_oit,
+        has_atmosphere,
     ) in views.iter_mut()
     {
         let mut view_key = MeshPipelineKey::from_msaa_samples(msaa.samples())
@@ -379,6 +385,10 @@ pub fn check_views_need_specialization(
             view_key |= MeshPipelineKey::OIT_ENABLED;
         }
 
+        if has_atmosphere {
+            view_key |= MeshPipelineKey::ATMOSPHERE;
+        }
+
         if let Some(projection) = projection {
             view_key |= match projection {
                 Projection::Perspective(_) => MeshPipelineKey::VIEW_PROJECTION_PERSPECTIVE,
@@ -2094,7 +2104,8 @@ bitflags::bitflags! {
         const HAS_PREVIOUS_MORPH                = 1 << 19;
         const OIT_ENABLED                       = 1 << 20;
         const DISTANCE_FOG                      = 1 << 21;
-        const LAST_FLAG                         = Self::DISTANCE_FOG.bits();
+        const ATMOSPHERE                        = 1 << 22;
+        const LAST_FLAG                         = Self::ATMOSPHERE.bits();
 
         // Bitfields
         const MSAA_RESERVED_BITS                = Self::MSAA_MASK_BITS << Self::MSAA_SHIFT_BITS;
@@ -2564,6 +2575,10 @@ impl SpecializedMeshPipeline for MeshPipeline {
             shader_defs.push("DISTANCE_FOG".into());
         }
 
+        if key.contains(MeshPipelineKey::ATMOSPHERE) {
+            shader_defs.push("ATMOSPHERE".into());
+        }
+
         if self.binding_arrays_are_usable {
             shader_defs.push("MULTIPLE_LIGHT_PROBES_IN_ARRAY".into());
             shader_defs.push("MULTIPLE_LIGHTMAPS_IN_ARRAY".into());