Exposure settings (adopted) (#11347)

Rebased and finished version of
#8407. Huge thanks to @GitGhillie
for adjusting all the examples, and the many other people who helped
write this PR (@superdump , @coreh , among others) :)

Fixes #8369

---

## Changelog
- Added a `brightness` control to `Skybox`.
- Added an `intensity` control to `EnvironmentMapLight`.
- Added `ExposureSettings` and `PhysicalCameraParameters` for
controlling exposure of 3D cameras.
- Removed the baked-in `DirectionalLight` exposure Bevy previously
hardcoded internally.

## Migration Guide
- If using a `Skybox` or `EnvironmentMapLight`, use the new `brightness`
and `intensity` controls to adjust their strength.
- All 3D scene will now have different apparent brightnesses due to Bevy
implementing proper exposure controls. You will have to adjust the
intensity of your lights and/or your camera exposure via the new
`ExposureSettings` component to compensate.

---------

Co-authored-by: Robert Swain <robert.swain@gmail.com>
Co-authored-by: GitGhillie <jillisnoordhoek@gmail.com>
Co-authored-by: Marco Buono <thecoreh@gmail.com>
Co-authored-by: vero <email@atlasdostal.com>
Co-authored-by: atlas dostal <rodol@rivalrebels.com>

crates/bevy_core_pipeline/src/core_3d/main_opaque_pass_3d_node.rs

@@ -76,13 +76,17 @@ impl ViewNode for MainOpaquePass3dNode {
         }
 
         // Draw the skybox using a fullscreen triangle
-        if let (Some(skybox_pipeline), Some(skybox_bind_group)) =
+        if let (Some(skybox_pipeline), Some(SkyboxBindGroup(skybox_bind_group))) =
             (skybox_pipeline, skybox_bind_group)
         {
             let pipeline_cache = world.resource::<PipelineCache>();
             if let Some(pipeline) = pipeline_cache.get_render_pipeline(skybox_pipeline.0) {
                 render_pass.set_render_pipeline(pipeline);
-                render_pass.set_bind_group(0, &skybox_bind_group.0, &[view_uniform_offset.offset]);
+                render_pass.set_bind_group(
+                    0,
+                    &skybox_bind_group.0,
+                    &[view_uniform_offset.offset, skybox_bind_group.1],
+                );
                 render_pass.draw(0..3, 0..1);
             }
         }

crates/bevy_core_pipeline/src/skybox/mod.rs

@@ -2,21 +2,20 @@ use bevy_app::{App, Plugin};
 use bevy_asset::{load_internal_asset, Handle};
 use bevy_ecs::{
     prelude::{Component, Entity},
-    query::With,
+    query::{QueryItem, With},
     schedule::IntoSystemConfigs,
     system::{Commands, Query, Res, ResMut, Resource},
 };
 use bevy_render::{
-    extract_component::{ExtractComponent, ExtractComponentPlugin},
+    camera::ExposureSettings,
+    extract_component::{
+        ComponentUniforms, DynamicUniformIndex, ExtractComponent, ExtractComponentPlugin,
+        UniformComponentPlugin,
+    },
     render_asset::RenderAssets,
     render_resource::{
         binding_types::{sampler, texture_cube, uniform_buffer},
-        BindGroup, BindGroupEntries, BindGroupLayout, BindGroupLayoutEntries,
-        CachedRenderPipelineId, ColorTargetState, ColorWrites, CompareFunction, DepthBiasState,
-        DepthStencilState, FragmentState, MultisampleState, PipelineCache, PrimitiveState,
-        RenderPipelineDescriptor, SamplerBindingType, Shader, ShaderStages,
-        SpecializedRenderPipeline, SpecializedRenderPipelines, StencilFaceState, StencilState,
-        TextureFormat, TextureSampleType, VertexState,
+        *,
     },
     renderer::RenderDevice,
     texture::{BevyDefault, Image},
@@ -34,7 +33,10 @@ impl Plugin for SkyboxPlugin {
     fn build(&self, app: &mut App) {
         load_internal_asset!(app, SKYBOX_SHADER_HANDLE, "skybox.wgsl", Shader::from_wgsl);
 
-        app.add_plugins(ExtractComponentPlugin::<Skybox>::default());
+        app.add_plugins((
+            ExtractComponentPlugin::<Skybox>::default(),
+            UniformComponentPlugin::<SkyboxUniforms>::default(),
+        ));
 
         let Ok(render_app) = app.get_sub_app_mut(RenderApp) else {
             return;
@@ -68,8 +70,41 @@ impl Plugin for SkyboxPlugin {
 /// To do so, use `EnvironmentMapLight` alongside this component.
 ///
 /// See also <https://en.wikipedia.org/wiki/Skybox_(video_games)>.
-#[derive(Component, ExtractComponent, Clone)]
-pub struct Skybox(pub Handle<Image>);
+#[derive(Component, Clone)]
+pub struct Skybox {
+    pub image: Handle<Image>,
+    /// Scale factor applied to the skybox image.
+    /// After applying this multiplier to the image samples, the resulting values should
+    /// be in units of [cd/m^2](https://en.wikipedia.org/wiki/Candela_per_square_metre).
+    pub brightness: f32,
+}
+
+impl ExtractComponent for Skybox {
+    type Data = (&'static Self, Option<&'static ExposureSettings>);
+    type Filter = ();
+    type Out = (Self, SkyboxUniforms);
+
+    fn extract_component(
+        (skybox, exposure_settings): QueryItem<'_, Self::Data>,
+    ) -> Option<Self::Out> {
+        let exposure = exposure_settings
+            .map(|e| e.exposure())
+            .unwrap_or_else(|| ExposureSettings::default().exposure());
+
+        Some((
+            skybox.clone(),
+            SkyboxUniforms {
+                brightness: skybox.brightness * exposure,
+            },
+        ))
+    }
+}
+
+// TODO: Replace with a push constant once WebGPU gets support for that
+#[derive(Component, ShaderType, Clone)]
+pub struct SkyboxUniforms {
+    brightness: f32,
+}
 
 #[derive(Resource)]
 struct SkyboxPipeline {
@@ -88,6 +123,7 @@ impl SkyboxPipeline {
                         sampler(SamplerBindingType::Filtering),
                         uniform_buffer::<ViewUniform>(true)
                             .visibility(ShaderStages::VERTEX_FRAGMENT),
+                        uniform_buffer::<SkyboxUniforms>(true),
                     ),
                 ),
             ),
@@ -186,31 +222,37 @@ fn prepare_skybox_pipelines(
 }
 
 #[derive(Component)]
-pub struct SkyboxBindGroup(pub BindGroup);
+pub struct SkyboxBindGroup(pub (BindGroup, u32));
 
 fn prepare_skybox_bind_groups(
     mut commands: Commands,
     pipeline: Res<SkyboxPipeline>,
     view_uniforms: Res<ViewUniforms>,
+    skybox_uniforms: Res<ComponentUniforms<SkyboxUniforms>>,
     images: Res<RenderAssets<Image>>,
     render_device: Res<RenderDevice>,
-    views: Query<(Entity, &Skybox)>,
+    views: Query<(Entity, &Skybox, &DynamicUniformIndex<SkyboxUniforms>)>,
 ) {
-    for (entity, skybox) in &views {
-        if let (Some(skybox), Some(view_uniforms)) =
-            (images.get(&skybox.0), view_uniforms.uniforms.binding())
-        {
+    for (entity, skybox, skybox_uniform_index) in &views {
+        if let (Some(skybox), Some(view_uniforms), Some(skybox_uniforms)) = (
+            images.get(&skybox.image),
+            view_uniforms.uniforms.binding(),
+            skybox_uniforms.binding(),
+        ) {
             let bind_group = render_device.create_bind_group(
                 "skybox_bind_group",
                 &pipeline.bind_group_layout,
                 &BindGroupEntries::sequential((
                     &skybox.texture_view,
                     &skybox.sampler,
                     view_uniforms,
+                    skybox_uniforms,
                 )),
             );
 
-            commands.entity(entity).insert(SkyboxBindGroup(bind_group));
+            commands
+                .entity(entity)
+                .insert(SkyboxBindGroup((bind_group, skybox_uniform_index.index())));
         }
     }
 }

crates/bevy_core_pipeline/src/skybox/skybox.wgsl

@@ -4,6 +4,7 @@
 @group(0) @binding(0) var skybox: texture_cube<f32>;
 @group(0) @binding(1) var skybox_sampler: sampler;
 @group(0) @binding(2) var<uniform> view: View;
+@group(0) @binding(3) var<uniform> brightness: f32;
 
 fn coords_to_ray_direction(position: vec2<f32>, viewport: vec4<f32>) -> vec3<f32> {
     // Using world positions of the fragment and camera to calculate a ray direction
@@ -62,5 +63,5 @@ fn skybox_fragment(in: VertexOutput) -> @location(0) vec4<f32> {
     let ray_direction = coords_to_ray_direction(in.position.xy, view.viewport);
 
     // Cube maps are left-handed so we negate the z coordinate.
-    return textureSample(skybox, skybox_sampler, ray_direction * vec3(1.0, 1.0, -1.0));
+    return textureSample(skybox, skybox_sampler, ray_direction * vec3(1.0, 1.0, -1.0)) * brightness;
 }

crates/bevy_pbr/src/environment_map/environment_map.wgsl

@@ -44,7 +44,7 @@ fn environment_map_light(
     let kD = diffuse_color * Edss;
 
     var out: EnvironmentMapLight;
-    out.diffuse = (FmsEms + kD) * irradiance;
-    out.specular = FssEss * radiance;
+    out.diffuse = (FmsEms + kD) * irradiance * bindings::lights.environment_map_intensity;
+    out.specular = FssEss * radiance * bindings::lights.environment_map_intensity;
     return out;
 }

crates/bevy_pbr/src/environment_map/mod.rs

@@ -51,6 +51,13 @@ impl Plugin for EnvironmentMapPlugin {
 pub struct EnvironmentMapLight {
     pub diffuse_map: Handle<Image>,
     pub specular_map: Handle<Image>,
+    /// Scale factor applied to the diffuse and specular light generated by this component.
+    ///
+    /// After applying this multiplier, the resulting values should
+    /// be in units of [cd/m^2](https://en.wikipedia.org/wiki/Candela_per_square_metre).
+    ///
+    /// See also <https://google.github.io/filament/Filament.html#lighting/imagebasedlights/iblunit>.
+    pub intensity: f32,
 }
 
 impl EnvironmentMapLight {

crates/bevy_pbr/src/light.rs

@@ -557,7 +557,7 @@ fn calculate_cascade(
 /// # use bevy_ecs::system::ResMut;
 /// # use bevy_pbr::AmbientLight;
 /// fn setup_ambient_light(mut ambient_light: ResMut<AmbientLight>) {
-///    ambient_light.brightness = 0.3;
+///    ambient_light.brightness = 20.0;
 /// }
 /// ```
 #[derive(Resource, Clone, Debug, ExtractResource, Reflect)]
@@ -572,7 +572,7 @@ impl Default for AmbientLight {
     fn default() -> Self {
         Self {
             color: Color::rgb(1.0, 1.0, 1.0),
-            brightness: 0.05,
+            brightness: 8.0,
         }
     }
 }

crates/bevy_pbr/src/render/light.rs

@@ -197,6 +197,7 @@ pub struct GpuLights {
     // offset from spot light's light index to spot light's shadow map index
     spot_light_shadowmap_offset: i32,
     environment_map_smallest_specular_mip_level: u32,
+    environment_map_intensity: f32,
 }
 
 // NOTE: this must be kept in sync with the same constants in pbr.frag
@@ -857,18 +858,6 @@ pub fn prepare_lights(
             flags |= DirectionalLightFlags::SHADOWS_ENABLED;
         }
 
-        // convert from illuminance (lux) to candelas
-        //
-        // exposure is hard coded at the moment but should be replaced
-        // by values coming from the camera
-        // see: https://google.github.io/filament/Filament.html#imagingpipeline/physicallybasedcamera/exposuresettings
-        const APERTURE: f32 = 4.0;
-        const SHUTTER_SPEED: f32 = 1.0 / 250.0;
-        const SENSITIVITY: f32 = 100.0;
-        let ev100 = f32::log2(APERTURE * APERTURE / SHUTTER_SPEED) - f32::log2(SENSITIVITY / 100.0);
-        let exposure = 1.0 / (f32::powf(2.0, ev100) * 1.2);
-        let intensity = light.illuminance * exposure;
-
         let num_cascades = light
             .cascade_shadow_config
             .bounds
@@ -877,9 +866,9 @@ pub fn prepare_lights(
         gpu_directional_lights[index] = GpuDirectionalLight {
             // Filled in later.
             cascades: [GpuDirectionalCascade::default(); MAX_CASCADES_PER_LIGHT],
-            // premultiply color by intensity
+            // premultiply color by illuminance
             // we don't use the alpha at all, so no reason to multiply only [0..3]
-            color: Vec4::from_slice(&light.color.as_linear_rgba_f32()) * intensity,
+            color: Vec4::from_slice(&light.color.as_linear_rgba_f32()) * light.illuminance,
             // direction is negated to be ready for N.L
             dir_to_light: light.transform.back(),
             flags: flags.bits(),
@@ -972,6 +961,9 @@ pub fn prepare_lights(
                 .and_then(|env_map| images.get(&env_map.specular_map))
                 .map(|specular_map| specular_map.mip_level_count - 1)
                 .unwrap_or(0),
+            environment_map_intensity: environment_map
+                .map(|env_map| env_map.intensity)
+                .unwrap_or(1.0),
         };
 
         // TODO: this should select lights based on relevance to the view instead of the first ones that show up in a query

crates/bevy_pbr/src/render/mesh_view_types.wgsl

@@ -58,6 +58,7 @@ struct Lights {
     n_directional_lights: u32,
     spot_light_shadowmap_offset: i32,
     environment_map_smallest_specular_mip_level: u32,
+    environment_map_intensity: f32,
 };
 
 struct Fog {

crates/bevy_pbr/src/render/pbr_functions.wgsl

@@ -386,7 +386,7 @@ fn apply_pbr_lighting(
 
     // Total light
     output_color = vec4<f32>(
-        transmitted_light + direct_light + indirect_light + emissive_light,
+        view_bindings::view.exposure * (transmitted_light + direct_light + indirect_light + emissive_light),
         output_color.a
     );
 
@@ -423,7 +423,7 @@ fn apply_fog(fog_params: mesh_view_types::Fog, input_color: vec4<f32>, fragment_
                     0.0
                 ),
                 fog_params.directional_light_exponent
-            ) * light.color.rgb;
+            ) * light.color.rgb * view_bindings::view.exposure;
         }
     }
 

crates/bevy_pbr/src/render/pbr_transmission.wgsl

@@ -42,6 +42,9 @@ fn specular_transmissive_light(world_position: vec4<f32>, frag_coord: vec3<f32>,
         background_color = fetch_transmissive_background(offset_position, frag_coord, view_z, perceptual_roughness);
     }
 
+    // Compensate for exposure, since the background color is coming from an already exposure-adjusted texture
+    background_color = vec4(background_color.rgb / view_bindings::view.exposure, background_color.a);
+
     // Dot product of the refracted direction with the exit normal (Note: We assume the exit normal is the entry normal but inverted)
     let MinusNdotT = dot(-N, T);