Better depth biases (#23)

* 3d_scene_pipelined: Use a shallower directional light angle to provoke acne

* cornell_box_pipelined: Remove bias tweaks

* bevy_pbr2: Simplify shadow biases by moving them to linear depth

examples/3d/3d_scene_pipelined.rs

@@ -199,7 +199,7 @@ fn setup(
         },
         transform: Transform {
             translation: Vec3::new(0.0, 2.0, 0.0),
-            rotation: Quat::from_rotation_x(-1.2),
+            rotation: Quat::from_rotation_x(-std::f32::consts::FRAC_PI_4),
             ..Default::default()
         },
         ..Default::default()

examples/3d/cornell_box_pipelined.rs

@@ -136,8 +136,6 @@ fn setup(
             builder.spawn_bundle(PointLightBundle {
                 point_light: PointLight {
                     color: Color::WHITE,
-                    shadow_bias_min: 0.00001,
-                    shadow_bias_max: 0.0001,
                     intensity: 25.0,
                     ..Default::default()
                 },
@@ -150,8 +148,6 @@ fn setup(
     commands.spawn_bundle(DirectionalLightBundle {
         directional_light: DirectionalLight {
             illuminance: 10000.0,
-            shadow_bias_min: 0.00001,
-            shadow_bias_max: 0.0001,
             shadow_projection: OrthographicProjection {
                 left: -HALF_SIZE,
                 right: HALF_SIZE,

pipelined/bevy_pbr2/src/light.rs

@@ -7,8 +7,8 @@ pub struct PointLight {
     pub intensity: f32,
     pub range: f32,
     pub radius: f32,
-    pub shadow_bias_min: f32,
-    pub shadow_bias_max: f32,
+    pub shadow_depth_bias: f32,
+    pub shadow_normal_bias: f32,
 }
 
 impl Default for PointLight {
@@ -18,15 +18,15 @@ impl Default for PointLight {
             intensity: 200.0,
             range: 20.0,
             radius: 0.0,
-            shadow_bias_min: Self::DEFAULT_SHADOW_BIAS_MIN,
-            shadow_bias_max: Self::DEFAULT_SHADOW_BIAS_MAX,
+            shadow_depth_bias: Self::DEFAULT_SHADOW_DEPTH_BIAS,
+            shadow_normal_bias: Self::DEFAULT_SHADOW_NORMAL_BIAS,
         }
     }
 }
 
 impl PointLight {
-    pub const DEFAULT_SHADOW_BIAS_MIN: f32 = 0.00005;
-    pub const DEFAULT_SHADOW_BIAS_MAX: f32 = 0.002;
+    pub const DEFAULT_SHADOW_DEPTH_BIAS: f32 = 0.02;
+    pub const DEFAULT_SHADOW_NORMAL_BIAS: f32 = 0.02;
 }
 
 /// A Directional light.
@@ -60,8 +60,8 @@ pub struct DirectionalLight {
     pub color: Color,
     pub illuminance: f32,
     pub shadow_projection: OrthographicProjection,
-    pub shadow_bias_min: f32,
-    pub shadow_bias_max: f32,
+    pub shadow_depth_bias: f32,
+    pub shadow_normal_bias: f32,
 }
 
 impl Default for DirectionalLight {
@@ -79,15 +79,15 @@ impl Default for DirectionalLight {
                 far: size,
                 ..Default::default()
             },
-            shadow_bias_min: Self::DEFAULT_SHADOW_BIAS_MIN,
-            shadow_bias_max: Self::DEFAULT_SHADOW_BIAS_MAX,
+            shadow_depth_bias: Self::DEFAULT_SHADOW_DEPTH_BIAS,
+            shadow_normal_bias: Self::DEFAULT_SHADOW_NORMAL_BIAS,
         }
     }
 }
 
 impl DirectionalLight {
-    pub const DEFAULT_SHADOW_BIAS_MIN: f32 = 0.00005;
-    pub const DEFAULT_SHADOW_BIAS_MAX: f32 = 0.002;
+    pub const DEFAULT_SHADOW_DEPTH_BIAS: f32 = 0.02;
+    pub const DEFAULT_SHADOW_NORMAL_BIAS: f32 = 0.02;
 }
 
 // Ambient light color.

pipelined/bevy_pbr2/src/render/light.rs

@@ -29,17 +29,17 @@ pub struct ExtractedPointLight {
     range: f32,
     radius: f32,
     transform: GlobalTransform,
-    shadow_bias_min: f32,
-    shadow_bias_max: f32,
+    shadow_depth_bias: f32,
+    shadow_normal_bias: f32,
 }
 
 pub struct ExtractedDirectionalLight {
     color: Color,
     illuminance: f32,
     direction: Vec3,
     projection: Mat4,
-    shadow_bias_min: f32,
-    shadow_bias_max: f32,
+    shadow_depth_bias: f32,
+    shadow_normal_bias: f32,
 }
 
 #[repr(C)]
@@ -52,8 +52,8 @@ pub struct GpuPointLight {
     radius: f32,
     near: f32,
     far: f32,
-    shadow_bias_min: f32,
-    shadow_bias_max: f32,
+    shadow_depth_bias: f32,
+    shadow_normal_bias: f32,
 }
 
 #[repr(C)]
@@ -62,8 +62,8 @@ pub struct GpuDirectionalLight {
     view_projection: Mat4,
     color: Vec4,
     dir_to_light: Vec3,
-    shadow_bias_min: f32,
-    shadow_bias_max: f32,
+    shadow_depth_bias: f32,
+    shadow_normal_bias: f32,
 }
 
 #[repr(C)]
@@ -235,8 +235,8 @@ pub fn extract_lights(
             range: point_light.range,
             radius: point_light.radius,
             transform: *transform,
-            shadow_bias_min: point_light.shadow_bias_min,
-            shadow_bias_max: point_light.shadow_bias_max,
+            shadow_depth_bias: point_light.shadow_depth_bias,
+            shadow_normal_bias: point_light.shadow_normal_bias,
         });
     }
     for (entity, directional_light, transform) in directional_lights.iter() {
@@ -247,8 +247,8 @@ pub fn extract_lights(
                 illuminance: directional_light.illuminance,
                 direction: transform.forward(),
                 projection: directional_light.shadow_projection.get_projection_matrix(),
-                shadow_bias_min: directional_light.shadow_bias_min,
-                shadow_bias_max: directional_light.shadow_bias_max,
+                shadow_depth_bias: directional_light.shadow_depth_bias,
+                shadow_normal_bias: directional_light.shadow_normal_bias,
             });
     }
 }
@@ -443,8 +443,8 @@ pub fn prepare_lights(
                 near: 0.1,
                 far: light.range,
                 // proj: projection,
-                shadow_bias_min: light.shadow_bias_min,
-                shadow_bias_max: light.shadow_bias_max,
+                shadow_depth_bias: light.shadow_depth_bias,
+                shadow_normal_bias: light.shadow_normal_bias,
             };
         }
 
@@ -482,8 +482,8 @@ pub fn prepare_lights(
                 dir_to_light,
                 // NOTE: * view is correct, it should not be view.inverse() here
                 view_projection: projection * view,
-                shadow_bias_min: light.shadow_bias_min,
-                shadow_bias_max: light.shadow_bias_max,
+                shadow_depth_bias: light.shadow_depth_bias,
+                shadow_normal_bias: light.shadow_normal_bias,
             };
 
             let depth_texture_view =

pipelined/bevy_pbr2/src/render/pbr.wgsl

@@ -95,16 +95,16 @@ struct PointLight {
     radius: f32;
     near: f32;
     far: f32;
-    shadow_bias_min: f32;
-    shadow_bias_max: f32;
+    shadow_depth_bias: f32;
+    shadow_normal_bias: f32;
 };
 
 struct DirectionalLight {
     view_projection: mat4x4<f32>;
     color: vec4<f32>;
     direction_to_light: vec3<f32>;
-    shadow_bias_min: f32;
-    shadow_bias_max: f32;
+    shadow_depth_bias: f32;
+    shadow_normal_bias: f32;
 };
 
 [[block]]
@@ -379,7 +379,7 @@ fn directional_light(light: DirectionalLight, roughness: f32, NdotV: f32, normal
     return (specular_light + diffuse) * light.color.rgb * NoL;
 }
 
-fn fetch_point_shadow(light_id: i32, frag_position: vec4<f32>, shadow_bias: f32) -> f32 {
+fn fetch_point_shadow(light_id: i32, frag_position: vec4<f32>) -> f32 {
     let light = lights.point_lights[light_id];
 
     // because the shadow maps align with the axes and the frustum planes are at 45 degrees
@@ -412,11 +412,12 @@ fn fetch_point_shadow(light_id: i32, frag_position: vec4<f32>, shadow_bias: f32)
     //       a quad (2x2 fragments) being processed not being sampled, and this messing with
     //       mip-mapping functionality. The shadow maps have no mipmaps so Level just samples
     //       from LOD 0.
-    let bias = 0.0001;
-    return textureSampleCompareLevel(point_shadow_textures, point_shadow_textures_sampler, frag_ls, i32(light_id), depth - shadow_bias);
+    return textureSampleCompareLevel(point_shadow_textures, point_shadow_textures_sampler, frag_ls, i32(light_id), depth);
 }
 
-fn fetch_directional_shadow(light_id: i32, homogeneous_coords: vec4<f32>, shadow_bias: f32) -> f32 {
+fn fetch_directional_shadow(light_id: i32, frag_position: vec4<f32>) -> f32 {
+    let light = lights.directional_lights[light_id];
+    let homogeneous_coords = light.view_projection * frag_position;
     if (homogeneous_coords.w <= 0.0) {
         return 1.0;
     }
@@ -428,7 +429,7 @@ fn fetch_directional_shadow(light_id: i32, homogeneous_coords: vec4<f32>, shadow
     // do the lookup, using HW PCF and comparison
     // NOTE: Due to non-uniform control flow above, we must use the level variant of the texture
     //       sampler to avoid use of implicit derivatives causing possible undefined behavior.
-    return textureSampleCompareLevel(directional_shadow_textures, directional_shadow_textures_sampler, light_local, i32(light_id), homogeneous_coords.z * proj_correction - shadow_bias);
+    return textureSampleCompareLevel(directional_shadow_textures, directional_shadow_textures_sampler, light_local, i32(light_id), homogeneous_coords.z * proj_correction);
 }
 
 struct FragmentInput {
@@ -521,23 +522,27 @@ fn fragment(in: FragmentInput) -> [[location(0)]] vec4<f32> {
         let n_directional_lights = i32(lights.n_directional_lights);
         for (var i: i32 = 0; i < n_point_lights; i = i + 1) {
             let light = lights.point_lights[i];
-            let light_contrib = point_light(in.world_position.xyz, light, roughness, NdotV, N, V, R, F0, diffuse_color);
+
             let dir_to_light = normalize(light.position.xyz - in.world_position.xyz);
-            let shadow_bias = max(
-                light.shadow_bias_max * (1.0 - dot(in.world_normal, dir_to_light)),
-                light.shadow_bias_min
-            );
-            let shadow = fetch_point_shadow(i, in.world_position, shadow_bias);
+            let depth_bias = light.shadow_depth_bias * dir_to_light.xyz;
+            let NdotL = dot(dir_to_light.xyz, in.world_normal.xyz);
+            let normal_bias = light.shadow_normal_bias * (1.0 - NdotL) * in.world_normal.xyz;
+            let biased_position = vec4<f32>(in.world_position.xyz + depth_bias + normal_bias, in.world_position.w);
+
+            let shadow = fetch_point_shadow(i, biased_position);
+            let light_contrib = point_light(in.world_position.xyz, light, roughness, NdotV, N, V, R, F0, diffuse_color);
             light_accum = light_accum + light_contrib * shadow;
         }
         for (var i: i32 = 0; i < n_directional_lights; i = i + 1) {
             let light = lights.directional_lights[i];
+
+            let depth_bias = light.shadow_depth_bias * light.direction_to_light.xyz;
+            let NdotL = dot(light.direction_to_light.xyz, in.world_normal.xyz);
+            let normal_bias = light.shadow_normal_bias * (1.0 - NdotL) * in.world_normal.xyz;
+            let biased_position = vec4<f32>(in.world_position.xyz + depth_bias + normal_bias, in.world_position.w);
+
+            let shadow = fetch_directional_shadow(i, biased_position);
             let light_contrib = directional_light(light, roughness, NdotV, N, V, R, F0, diffuse_color);
-            let shadow_bias = max(
-                light.shadow_bias_max * (1.0 - dot(in.world_normal, light.direction_to_light.xyz)),
-                light.shadow_bias_min
-            );
-            let shadow = fetch_directional_shadow(i, light.view_projection * in.world_position, shadow_bias);
             light_accum = light_accum + light_contrib * shadow;
         }