Better cascades config defaults + builder, tweak example configs (#7456)

# Objective

- Improve ergonomics / documentation of cascaded shadow maps
- Allow for the customization of the nearest shadowing distance.
- Fixes #7393 
- Fixes #7362 

## Solution

- Introduce `CascadeShadowConfigBuilder`
- Tweak various example cascade settings for better quality.

---

## Changelog

- Made examples look nicer under cascaded shadow maps.
- Introduce `CascadeShadowConfigBuilder` to help with creating `CascadeShadowConfig`

## Migration Guide

- Configure settings for cascaded shadow maps for directional lights using the newly introduced `CascadeShadowConfigBuilder`.

Co-authored-by: Robert Swain <robert.swain@gmail.com>

crates/bevy_pbr/src/light.rs

@@ -226,31 +226,37 @@ pub struct DirectionalLightShadowMap {
 
 impl Default for DirectionalLightShadowMap {
     fn default() -> Self {
-        #[cfg(feature = "webgl")]
-        return Self { size: 1024 };
-        #[cfg(not(feature = "webgl"))]
-        return Self { size: 2048 };
+        Self { size: 2048 }
     }
 }
 
 /// Controls how cascaded shadow mapping works.
+/// Prefer using [`CascadeShadowConfigBuilder`] to construct an instance.
+///
+/// ```
+/// # use bevy_pbr::CascadeShadowConfig;
+/// # use bevy_pbr::CascadeShadowConfigBuilder;
+/// # use bevy_utils::default;
+/// #
+/// let config: CascadeShadowConfig = CascadeShadowConfigBuilder {
+///   maximum_distance: 100.0,
+///   ..default()
+/// }.into();
+/// ```
 #[derive(Component, Clone, Debug, Reflect)]
 #[reflect(Component)]
 pub struct CascadeShadowConfig {
     /// The (positive) distance to the far boundary of each cascade.
     pub bounds: Vec<f32>,
     /// The proportion of overlap each cascade has with the previous cascade.
     pub overlap_proportion: f32,
+    /// The (positive) distance to the near boundary of the first cascade.
+    pub minimum_distance: f32,
 }
 
 impl Default for CascadeShadowConfig {
     fn default() -> Self {
-        if cfg!(feature = "webgl") {
-            // Currently only support one cascade in webgl.
-            Self::new(1, 5.0, 100.0, 0.2)
-        } else {
-            Self::new(4, 5.0, 1000.0, 0.2)
-        }
+        CascadeShadowConfigBuilder::default().into()
     }
 }
 
@@ -268,31 +274,112 @@ fn calculate_cascade_bounds(
         .collect()
 }
 
-impl CascadeShadowConfig {
-    /// Returns a cascade config for `num_cascades` cascades, with the first cascade
-    /// having far bound `nearest_bound` and the last cascade having far bound `shadow_maximum_distance`.
-    /// In-between cascades will be exponentially spaced.
-    pub fn new(
-        num_cascades: usize,
-        nearest_bound: f32,
-        shadow_maximum_distance: f32,
-        overlap_proportion: f32,
-    ) -> Self {
+/// Builder for [`CascadeShadowConfig`].
+pub struct CascadeShadowConfigBuilder {
+    /// The number of shadow cascades.
+    /// More cascades increases shadow quality by mitigating perspective aliasing - a phenomenom where areas
+    /// nearer the camera are covered by fewer shadow map texels than areas further from the camera, causing
+    /// blocky looking shadows.
+    ///
+    /// This does come at the cost increased rendering overhead, however this overhead is still less
+    /// than if you were to use fewer cascades and much larger shadow map textures to achieve the
+    /// same quality level.
+    ///
+    /// In case rendered geometry covers a relatively narrow and static depth relative to camera, it may
+    /// make more sense to use fewer cascades and a higher resolution shadow map texture as perspective aliasing
+    /// is not as much an issue. Be sure to adjust `minimum_distance` and `maximum_distance` appropriately.
+    pub num_cascades: usize,
+    /// The minimum shadow distance, which can help improve the texel resolution of the first cascade.
+    /// Areas nearer to the camera than this will likely receive no shadows.
+    ///
+    /// NOTE: Due to implementation details, this usually does not impact shadow quality as much as
+    /// `first_cascade_far_bound` and `maximum_distance`. At many view frustum field-of-views, the
+    /// texel resolution of the first cascade is dominated by the width / height of the view frustum plane
+    /// at `first_cascade_far_bound` rather than the depth of the frustum from `minimum_distance` to
+    /// `first_cascade_far_bound`.
+    pub minimum_distance: f32,
+    /// The maximum shadow distance.
+    /// Areas further from the camera than this will likely receive no shadows.
+    pub maximum_distance: f32,
+    /// Sets the far bound of the first cascade, relative to the view origin.
+    /// In-between cascades will be exponentially spaced relative to the maximum shadow distance.
+    /// NOTE: This is ignored if there is only one cascade, the maximum distance takes precedence.
+    pub first_cascade_far_bound: f32,
+    /// Sets the overlap proportion between cascades.
+    /// The overlap is used to make the transition from one cascade's shadow map to the next
+    /// less abrupt by blending between both shadow maps.
+    pub overlap_proportion: f32,
+}
+
+impl CascadeShadowConfigBuilder {
+    /// Returns the cascade config as specified by this builder.
+    pub fn build(&self) -> CascadeShadowConfig {
         assert!(
-            num_cascades > 0,
-            "num_cascades must be positive, but was {num_cascades}",
+            self.num_cascades > 0,
+            "num_cascades must be positive, but was {}",
+            self.num_cascades
         );
         assert!(
-            (0.0..1.0).contains(&overlap_proportion),
-            "overlap_proportion must be in [0.0, 1.0) but was {overlap_proportion}",
+            self.minimum_distance >= 0.0,
+            "maximum_distance must be non-negative, but was {}",
+            self.minimum_distance
         );
-        Self {
-            bounds: calculate_cascade_bounds(num_cascades, nearest_bound, shadow_maximum_distance),
-            overlap_proportion,
+        assert!(
+            self.num_cascades == 1 || self.minimum_distance < self.first_cascade_far_bound,
+            "minimum_distance must be less than first_cascade_far_bound, but was {}",
+            self.minimum_distance
+        );
+        assert!(
+            self.maximum_distance > self.minimum_distance,
+            "maximum_distance must be greater than minimum_distance, but was {}",
+            self.maximum_distance
+        );
+        assert!(
+            (0.0..1.0).contains(&self.overlap_proportion),
+            "overlap_proportion must be in [0.0, 1.0) but was {}",
+            self.overlap_proportion
+        );
+        CascadeShadowConfig {
+            bounds: calculate_cascade_bounds(
+                self.num_cascades,
+                self.first_cascade_far_bound,
+                self.maximum_distance,
+            ),
+            overlap_proportion: self.overlap_proportion,
+            minimum_distance: self.minimum_distance,
         }
     }
 }
 
+impl Default for CascadeShadowConfigBuilder {
+    fn default() -> Self {
+        if cfg!(feature = "webgl") {
+            // Currently only support one cascade in webgl.
+            Self {
+                num_cascades: 1,
+                minimum_distance: 0.1,
+                maximum_distance: 100.0,
+                first_cascade_far_bound: 5.0,
+                overlap_proportion: 0.2,
+            }
+        } else {
+            Self {
+                num_cascades: 4,
+                minimum_distance: 0.1,
+                maximum_distance: 1000.0,
+                first_cascade_far_bound: 5.0,
+                overlap_proportion: 0.2,
+            }
+        }
+    }
+}
+
+impl From<CascadeShadowConfigBuilder> for CascadeShadowConfig {
+    fn from(builder: CascadeShadowConfigBuilder) -> Self {
+        builder.build()
+    }
+}
+
 #[derive(Component, Clone, Debug, Default, Reflect)]
 #[reflect(Component)]
 pub struct Cascades {
@@ -375,7 +462,7 @@ pub fn update_directional_light_cascades(
                             (1.0 - cascades_config.overlap_proportion)
                                 * -cascades_config.bounds[idx - 1]
                         } else {
-                            0.0
+                            -cascades_config.minimum_distance
                         },
                         -far_bound,
                     )

crates/bevy_pbr/src/render/pbr_functions.wgsl

@@ -226,7 +226,10 @@ fn pbr(
                 && (lights.directional_lights[i].flags & DIRECTIONAL_LIGHT_FLAGS_SHADOWS_ENABLED_BIT) != 0u) {
             shadow = fetch_directional_shadow(i, in.world_position, in.world_normal, view_z);
         }
-        let light_contrib = directional_light(i, roughness, NdotV, in.N, in.V, R, F0, diffuse_color);
+        var light_contrib = directional_light(i, roughness, NdotV, in.N, in.V, R, F0, diffuse_color);
+#ifdef DIRECTIONAL_LIGHT_SHADOW_MAP_DEBUG_CASCADES
+        light_contrib = cascade_debug_visualization(light_contrib, i, view_z);
+#endif
         light_accum = light_accum + light_contrib * shadow;
     }
 

crates/bevy_pbr/src/render/shadows.wgsl

@@ -144,22 +144,22 @@ fn sample_cascade(light_id: u32, cascade_index: u32, frag_position: vec4<f32>, s
         directional_shadow_textures_sampler,
         light_local,
         depth
-    );   
+    );
 #else
     return textureSampleCompareLevel(
         directional_shadow_textures,
         directional_shadow_textures_sampler,
         light_local,
         i32((*light).depth_texture_base_index + cascade_index),
         depth
-    );   
+    );
 #endif
 }
 
 fn fetch_directional_shadow(light_id: u32, frag_position: vec4<f32>, surface_normal: vec3<f32>, view_z: f32) -> f32 {
     let light = &lights.directional_lights[light_id];
     let cascade_index = get_cascade_index(light_id, view_z);
-    
+
     if (cascade_index >= (*light).num_cascades) {
         return 1.0;
     }
@@ -178,3 +178,16 @@ fn fetch_directional_shadow(light_id: u32, frag_position: vec4<f32>, surface_nor
     }
     return shadow;
 }
+
+fn cascade_debug_visualization(
+    output_color: vec3<f32>,
+    light_id: u32,
+    view_z: f32,
+) -> vec3<f32> {
+    let overlay_alpha = 0.95;
+    let cascade_index = get_cascade_index(light_id, view_z);
+    let cascade_color = hsv2rgb(f32(cascade_index) / f32(#{MAX_CASCADES_PER_LIGHT}u + 1u), 1.0, 0.5);
+    return vec3<f32>(
+        (1.0 - overlay_alpha) * output_color.rgb + overlay_alpha * cascade_color
+    );
+}

examples/3d/atmospheric_fog.rs

@@ -8,7 +8,7 @@
 //! | `S`                | Toggle Directional Light Fog Influence |
 
 use bevy::{
-    pbr::{CascadeShadowConfig, NotShadowCaster},
+    pbr::{CascadeShadowConfigBuilder, NotShadowCaster},
     prelude::*,
 };
 
@@ -49,9 +49,12 @@ fn setup_terrain_scene(
     asset_server: Res<AssetServer>,
 ) {
     // Configure a properly scaled cascade shadow map for this scene (defaults are too large, mesh units are in km)
-    // For WebGL we only support 1 cascade level for now
-    let cascade_shadow_config =
-        CascadeShadowConfig::new(if cfg!(feature = "webgl") { 1 } else { 4 }, 0.5, 2.5, 0.2);
+    let cascade_shadow_config = CascadeShadowConfigBuilder {
+        first_cascade_far_bound: 0.3,
+        maximum_distance: 3.0,
+        ..default()
+    }
+    .build();
 
     // Sun
     commands.spawn(DirectionalLightBundle {

examples/3d/fxaa.rs

@@ -4,6 +4,7 @@ use std::f32::consts::PI;
 
 use bevy::{
     core_pipeline::fxaa::{Fxaa, Sensitivity},
+    pbr::CascadeShadowConfigBuilder,
     prelude::*,
     render::{
         render_resource::{Extent3d, SamplerDescriptor, TextureDimension, TextureFormat},
@@ -81,6 +82,12 @@ fn setup(
             PI * -0.15,
             PI * -0.15,
         )),
+        cascade_shadow_config: CascadeShadowConfigBuilder {
+            maximum_distance: 3.0,
+            first_cascade_far_bound: 0.9,
+            ..default()
+        }
+        .into(),
         ..default()
     });
 

examples/3d/lighting.rs

@@ -3,7 +3,7 @@
 
 use std::f32::consts::PI;
 
-use bevy::{pbr::CascadeShadowConfig, prelude::*};
+use bevy::{pbr::CascadeShadowConfigBuilder, prelude::*};
 
 fn main() {
     App::new()
@@ -198,8 +198,13 @@ fn setup(
         },
         // The default cascade config is designed to handle large scenes.
         // As this example has a much smaller world, we can tighten the shadow
-        // far bound for better visual quality.
-        cascade_shadow_config: CascadeShadowConfig::new(4, 5.0, 30.0, 0.2),
+        // bounds for better visual quality.
+        cascade_shadow_config: CascadeShadowConfigBuilder {
+            first_cascade_far_bound: 4.0,
+            maximum_distance: 10.0,
+            ..default()
+        }
+        .into(),
         ..default()
     });
 

examples/3d/load_gltf.rs

@@ -2,14 +2,18 @@
 
 use std::f32::consts::*;
 
-use bevy::{pbr::CascadeShadowConfig, prelude::*};
+use bevy::{
+    pbr::{CascadeShadowConfigBuilder, DirectionalLightShadowMap},
+    prelude::*,
+};
 
 fn main() {
     App::new()
         .insert_resource(AmbientLight {
             color: Color::WHITE,
             brightness: 1.0 / 5.0f32,
         })
+        .insert_resource(DirectionalLightShadowMap { size: 4096 })
         .add_plugins(DefaultPlugins)
         .add_startup_system(setup)
         .add_system(animate_light_direction)
@@ -28,7 +32,14 @@ fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
         },
         // This is a relatively small scene, so use tighter shadow
         // cascade bounds than the default for better quality.
-        cascade_shadow_config: CascadeShadowConfig::new(1, 1.1, 1.5, 0.3),
+        // We also adjusted the shadow map to be larger since we're
+        // only using a single cascade.
+        cascade_shadow_config: CascadeShadowConfigBuilder {
+            num_cascades: 1,
+            maximum_distance: 1.6,
+            ..default()
+        }
+        .into(),
         ..default()
     });
     commands.spawn(SceneBundle {

examples/3d/shadow_caster_receiver.rs

@@ -3,7 +3,7 @@
 use std::f32::consts::PI;
 
 use bevy::{
-    pbr::{NotShadowCaster, NotShadowReceiver},
+    pbr::{CascadeShadowConfigBuilder, NotShadowCaster, NotShadowReceiver},
     prelude::*,
 };
 
@@ -109,6 +109,12 @@ fn setup(
             PI / 2.,
             -PI / 4.,
         )),
+        cascade_shadow_config: CascadeShadowConfigBuilder {
+            first_cascade_far_bound: 7.0,
+            maximum_distance: 25.0,
+            ..default()
+        }
+        .into(),
         ..default()
     });
 

examples/3d/split_screen.rs

@@ -3,8 +3,8 @@
 use std::f32::consts::PI;
 
 use bevy::{
-    core_pipeline::clear_color::ClearColorConfig, prelude::*, render::camera::Viewport,
-    window::WindowResized,
+    core_pipeline::clear_color::ClearColorConfig, pbr::CascadeShadowConfigBuilder, prelude::*,
+    render::camera::Viewport, window::WindowResized,
 };
 
 fn main() {
@@ -41,6 +41,13 @@ fn setup(
             shadows_enabled: true,
             ..default()
         },
+        cascade_shadow_config: CascadeShadowConfigBuilder {
+            num_cascades: 2,
+            first_cascade_far_bound: 200.0,
+            maximum_distance: 280.0,
+            ..default()
+        }
+        .into(),
         ..default()
     });