Diffuse Roughness support (#16253)

This PR replaces #16183

This PR implements the base_diffuse_roughness parameter from the
[OpenPBR
specification](https://academysoftwarefoundation.github.io/OpenPBR/#model/basesubstrate).

The diffuse roughness is implemented for analytic lights,
realtime-filtered IBL, prefiltered IBL and spherical harmonics.
I've added a flag to a material to choose between Lambert, Burley and
the new Energy Conserving Oren-Nayar (EON) model used by OpenPBR. The
default is OpenPBR's EON model.

The previous behaviour was to use Burley diffuse for analytical lights
and Lambert for IBL. Also, previously, specular roughness was applied to
diffuse roughness for analytical lights while IBL didn't use it at all
(because it was simply Lambertian). So, the new default slightly changes
existing projects that used analytical lights but I question how
noticeable that will be.

**Analytical Light:**

https://playground.babylonjs.com/?snapshot=refs/pull/16253/merge#MXACV7#3

![roughnessCompare](https://github.com/user-attachments/assets/df0f6782-f1c9-42b3-8c82-d2e4ebc59f85)

**Realtime IBL:**

https://playground.babylonjs.com/?snapshot=refs/pull/16253/merge#MXACV7#5
<img width="881" alt="image"
src="https://github.com/user-attachments/assets/4d33b49c-a8d5-4903-85ca-78eb368c015e"
/>

The diffuse roughness models are heavily dependent on the light
direction and view direction and are therefore difficult to handle with
a prefiltered IBL. I came up with two methods for approximating
roughness with prefiltered IBL's. The first, if we prefiltered using
CDF, we generate a dominant light direction to use in the BRDF
calculations. It works reasonably well.

**Prefiltered IBL with CDF:**

https://playground.babylonjs.com/?snapshot=refs/pull/16253/merge#MXACV7#9
<img width="883" alt="image"
src="https://github.com/user-attachments/assets/b4c8383b-30be-4505-a09c-3bc5d6ee4cc3"
/>

The second approach, if you don't use CDF, is by approximating roughness
by bending the surface normal towards the camera to add some of the
retro-reflective behaviour that you get with EON. Because of this,
you'll notice that Burley and EON are identical and the shadow
terminator appears to move as diffuse roughness increases. In practice,
however, this example uses an extreme IBL with a bright sunlight. With
other IBL's, the effect tends to be more convincing.

**Prefiltered IBL without CDF**

https://playground.babylonjs.com/?snapshot=refs/pull/16253/merge#MXACV7#10
<img width="878" alt="image"
src="https://github.com/user-attachments/assets/ffaa366c-6e9f-449a-8cbf-6364354e314f"
/>

The default IBL lighting in Sandbox uses spherical harmonics so we need
to approximate diffuse roughness with this as well. I'm using the same
bent normal technique as with prefiltered IBL without CDF.

**Spherical Harmonics IBL**

https://playground.babylonjs.com/?snapshot=refs/pull/16253/merge#MXACV7#11

![image](https://github.com/user-attachments/assets/13543a47-62aa-4d26-a438-1a6031803027)

---------

Co-authored-by: Julien Guertault <[email protected]>
Co-authored-by: Mike Bond <[email protected]>
Co-authored-by: Popov72 <[email protected]>

Author: 4 people

packages/dev/core/src/Engines/constants.ts

@@ -469,6 +469,21 @@ export class Constants {
      */
     public static readonly MATERIAL_CounterClockWiseSideOrientation = 1;
 
+    /**
+     * Energy-conserving Oren Nayar diffuse model type.
+     */
+    public static readonly MATERIAL_DIFFUSE_MODEL_E_OREN_NAYAR = 0;
+
+    /**
+     * Burley diffuse model type.
+     */
+    public static readonly MATERIAL_DIFFUSE_MODEL_BURLEY = 1;
+
+    /**
+     * Lambertian diffuse model type.
+     */
+    public static readonly MATERIAL_DIFFUSE_MODEL_LAMBERT = 2;
+
     /**
      * Nothing
      * @see https://doc.babylonjs.com/features/featuresDeepDive/events/actions#triggers

packages/dev/core/src/Materials/Node/Blocks/PBR/pbrMetallicRoughnessBlock.ts

@@ -97,6 +97,7 @@ export class PBRMetallicRoughnessBlock extends NodeMaterialBlock {
     private _metallicReflectanceColor: Color3 = Color3.White();
     private _metallicF0Factor = 1;
     private _vMetallicReflectanceFactorsName: string;
+    private _baseDiffuseRoughnessName: string;
 
     /**
      * Create a new ReflectionBlock
@@ -271,6 +272,19 @@ export class PBRMetallicRoughnessBlock extends NodeMaterialBlock {
     })
     public realTimeFilteringQuality = Constants.TEXTURE_FILTERING_QUALITY_LOW;
 
+    /**
+     * Base Diffuse Model
+     */
+    @editableInPropertyPage("Diffuse Model", PropertyTypeForEdition.List, "RENDERING", {
+        notifiers: { update: true },
+        options: [
+            { label: "Lambert", value: Constants.MATERIAL_DIFFUSE_MODEL_LAMBERT },
+            { label: "Burley", value: Constants.MATERIAL_DIFFUSE_MODEL_BURLEY },
+            { label: "Oren-Nayar", value: Constants.MATERIAL_DIFFUSE_MODEL_E_OREN_NAYAR },
+        ],
+    })
+    public baseDiffuseModel = Constants.MATERIAL_DIFFUSE_MODEL_E_OREN_NAYAR;
+
     /**
      * Defines if the material uses energy conservation.
      */
@@ -762,6 +776,8 @@ export class PBRMetallicRoughnessBlock extends NodeMaterialBlock {
             defines.setValue("NUM_SAMPLES", "" + this.realTimeFilteringQuality, true);
         }
 
+        defines.setValue("BASE_DIFFUSE_MODEL", this.baseDiffuseModel, true);
+
         // Advanced
         defines.setValue("BRDF_V_HEIGHT_CORRELATED", true);
         defines.setValue("MS_BRDF_ENERGY_CONSERVATION", this.useEnergyConservation, true);
@@ -1014,13 +1030,21 @@ export class PBRMetallicRoughnessBlock extends NodeMaterialBlock {
         this._vMetallicReflectanceFactorsName = state._getFreeVariableName("vMetallicReflectanceFactors");
         state._emitUniformFromString(this._vMetallicReflectanceFactorsName, NodeMaterialBlockConnectionPointTypes.Vector4);
 
+        this._baseDiffuseRoughnessName = state._getFreeVariableName("baseDiffuseRoughness");
+        state._emitUniformFromString(this._baseDiffuseRoughnessName, NodeMaterialBlockConnectionPointTypes.Float);
+
         code += `${state._declareLocalVar("baseColor", NodeMaterialBlockConnectionPointTypes.Vector3)} = surfaceAlbedo;
             ${isWebGPU ? "let" : `vec4${state.fSuffix}`} vReflectivityColor = vec4${state.fSuffix}(${this.metallic.associatedVariableName}, ${this.roughness.associatedVariableName}, ${this.indexOfRefraction.associatedVariableName || "1.5"}, 1.0);
             reflectivityOut = reflectivityBlock(
                 vReflectivityColor
             #ifdef METALLICWORKFLOW
                 , surfaceAlbedo
                 , ${(isWebGPU ? "uniforms." : "") + this._vMetallicReflectanceFactorsName}
+            #endif
+                , ${(isWebGPU ? "uniforms." : "") + this._baseDiffuseRoughnessName}
+            #ifdef BASE_DIFFUSE_ROUGHNESS
+                , 0.
+                , vec2${state.fSuffix}(0., 0.)
             #endif
             #ifdef REFLECTIVITY
                 , vec3${state.fSuffix}(0., 0., ${aoIntensity})
@@ -1036,6 +1060,7 @@ export class PBRMetallicRoughnessBlock extends NodeMaterialBlock {
 
             ${state._declareLocalVar("microSurface", NodeMaterialBlockConnectionPointTypes.Float)} = reflectivityOut.microSurface;
             ${state._declareLocalVar("roughness", NodeMaterialBlockConnectionPointTypes.Float)} = reflectivityOut.roughness;
+            ${state._declareLocalVar("diffuseRoughness", NodeMaterialBlockConnectionPointTypes.Float)} = reflectivityOut.diffuseRoughness;
 
             #ifdef METALLICWORKFLOW
                 surfaceAlbedo = reflectivityOut.surfaceAlbedo;

packages/dev/core/src/Materials/Node/Blocks/PBR/reflectionBlock.ts

@@ -438,6 +438,9 @@ export class ReflectionBlock extends ReflectionTextureBaseBlock {
             #ifdef USEIRRADIANCEMAP
                 , irradianceSampler         // ** not handled **
                 ${isWebGPU ? `, irradianceSamplerSampler` : ""}
+                #ifdef USE_IRRADIANCE_DOMINANT_DIRECTION
+                , vReflectionDominantDirection
+                #endif
             #endif
             #ifndef LODBASEDMICROSFURACE
                 #ifdef ${this._define3DName}
@@ -459,6 +462,9 @@ export class ReflectionBlock extends ReflectionTextureBaseBlock {
                     ${isWebGPU ? `, icdfSamplerSampler` : ""}
                 #endif
             #endif
+            , viewDirectionW
+            , diffuseRoughness
+            , surfaceAlbedo
             );
         #endif\n`;