Add and expose distance attenuation to compensate low-res shadow maps

Signed-off-by: Santi Paprika <santi.gonzalez.cs@gmail.com>

Gems/Atom/Feature/Common/Assets/Materials/Types/EnhancedPBR.materialtype

@@ -1239,7 +1239,7 @@
                 {
                     "name": "angleOffset",
                     "displayName": "    Angle Offset",
-                    "description": "Angle to accept below (N . L = 0) in scattering through thin objects",
+                    "description": "cosine of angle to extend below (N . L = 0) in scattering through thin objects",
                     "type": "float",
                     "defaultValue": 0.1,
                     "min": -1.0,
@@ -1249,6 +1249,19 @@
                         "name": "m_angleOffset"
                     }
                 },
+                {
+                    "name": "distanceAttenuation",
+                    "displayName": "    Distance Attenuation",
+                    "description": "Attenuation applied to hide artifacts due to low-res shadow maps (e.g. objects far to the camera when using directional lights or objects far to the light when using sphere/disk lights",
+                    "type": "float",
+                    "defaultValue": 4.0,
+                    "min": 0.0,
+                    "softMax": 10.0,
+                    "connection": {
+                        "type": "ShaderInput",
+                        "name": "m_distanceAttenuation"
+                    }
+                },
                 {
                     "name": "transmissionScale",
                     "displayName": "    Scale",

Gems/Atom/Feature/Common/Assets/Materials/Types/EnhancedPBR_Common.azsli

@@ -102,6 +102,7 @@ ShaderResourceGroup MaterialSrg : SRG_PerMaterial
     uint m_transmissionThicknessMapUvIndex;
     float m_shrinkFactor;
     float m_angleOffset;
+    float m_distanceAttenuation;
 }
 
 // Callback function for ParallaxMapping.azsli

Gems/Atom/Feature/Common/Assets/Materials/Types/EnhancedPBR_ForwardPass.azsl

@@ -283,6 +283,9 @@ PbrLightingOutput ForwardPassPS_Common(VSOutput IN, bool isFrontFace, out float
     // Shrink (absolute) offset towards the normal opposite direction to ensure correct shadow map projection
     lightingData.shrinkFactor = MaterialSrg::m_shrinkFactor;
 
+    // Attenuation applied to hide artifacts due to low-res shadow maps 
+    lightingData.distanceAttenuation = MaterialSrg::m_distanceAttenuation;
+
     // ------- Clearcoat -------
     
     // [GFX TODO][ATOM-14603]: Clean up the double uses of these clear coat flags

Gems/Atom/Feature/Common/Assets/Materials/Types/Skin.azsl

@@ -349,6 +349,9 @@ PbrLightingOutput SkinPS_Common(VSOutput IN)
     // Shrink (absolute) offset towards the normal opposite direction to ensure correct shadow map projection
     lightingData.shrinkFactor = MaterialSrg::m_shrinkFactor;
 
+    // Attenuation applied to hide artifacts due to low-res shadow maps 
+    lightingData.distanceAttenuation = MaterialSrg::m_distanceAttenuation;
+
     // ------- Occlusion -------
     
     lightingData.diffuseAmbientOcclusion = GetOcclusionInput(MaterialSrg::m_diffuseOcclusionMap, MaterialSrg::m_sampler, IN.m_uv[MaterialSrg::m_diffuseOcclusionMapUvIndex], MaterialSrg::m_diffuseOcclusionFactor, o_diffuseOcclusion_useTexture);

Gems/Atom/Feature/Common/Assets/Materials/Types/Skin.materialtype

@@ -653,7 +653,7 @@
                 {
                     "name": "angleOffset",
                     "displayName": "    Angle Offset",
-                    "description": "Angle to accept below (N . L = 0) in scattering through thin objects",
+                    "description": "cosine of angle to extend below (N . L = 0) in scattering through thin objects",
                     "type": "float",
                     "defaultValue": 0.1,
                     "min": -1.0,
@@ -663,6 +663,19 @@
                         "name": "m_angleOffset"
                     }
                 },
+                {
+                    "name": "distanceAttenuation",
+                    "displayName": "    Distance Attenuation",
+                    "description": "Attenuation applied to hide artifacts due to low-res shadow maps (e.g. objects far to the camera when using directional lights or objects far to the light when using sphere/disk lights",
+                    "type": "float",
+                    "defaultValue": 4.0,
+                    "min": 0.0,
+                    "softMax": 10.0,
+                    "connection": {
+                        "type": "ShaderInput",
+                        "name": "m_distanceAttenuation"
+                    }
+                },
                 {
                     "name": "transmissionScale",
                     "displayName": "    Scale",

Gems/Atom/Feature/Common/Assets/Materials/Types/Skin_Common.azsli

@@ -73,6 +73,7 @@ ShaderResourceGroup MaterialSrg : SRG_PerMaterial
     uint m_transmissionThicknessMapUvIndex;
     float m_shrinkFactor;
     float m_angleOffset;
+    float m_distanceAttenuation;
     
     Texture2D m_wrinkle_baseColor_texture1;
     Texture2D m_wrinkle_baseColor_texture2;

Gems/Atom/Feature/Common/Assets/ShaderLib/Atom/Features/PBR/Lighting/LightingData.azsli

@@ -37,6 +37,9 @@ class LightingData
     // Shrink (absolute) offset towards the normal opposite direction to ensure correct shadow map projection
     float shrinkFactor;
 
+    // Attenuation applied to hide artifacts due to low-res shadow maps 
+    float distanceAttenuation;
+
     // Normalized direction from surface to camera
     float3 dirToCamera;
     

Gems/Atom/Feature/Common/Assets/ShaderLib/Atom/Features/PBR/Lights/DirectionalLight.azsli

@@ -18,7 +18,7 @@ void ApplyDirectionalLights(Surface surface, inout LightingData lightingData)
     // Shadowed check
     const uint shadowIndex = ViewSrg::m_shadowIndexDirectionalLight;
     float litRatio = 1.0f;
-
+    float camToSurfDist = distance(ViewSrg::m_worldPosition, surface.position);
     // Transmission distance inside object
     float transmissionDistance = 0.0f;
 
@@ -84,7 +84,13 @@ void ApplyDirectionalLights(Surface surface, inout LightingData lightingData)
         
         lightingData.diffuseLighting += GetDiffuseLighting(surface, lightingData, light.m_rgbIntensityLux, dirToLight) * currentLitRatio;
         lightingData.specularLighting += GetSpecularLighting(surface, lightingData, light.m_rgbIntensityLux, dirToLight) * currentLitRatio;
-        lightingData.translucentBackLighting += GetBackLighting(surface, lightingData, light.m_rgbIntensityLux, dirToLight, currentTransmissionDistance);
+        
+        float3 backLighting = GetBackLighting(surface, lightingData, light.m_rgbIntensityLux, dirToLight, currentTransmissionDistance);
+        
+        // Attenuation applied to hide artifacts due to low-res shadow maps (might need some work in the future)
+        float attenuation = 1.0 / pow(max(1.0, camToSurfDist/2.0), lightingData.distanceAttenuation + 1.0);
+        
+        lightingData.translucentBackLighting += backLighting * attenuation;
     }
     
     // Add debug coloring for directional light shadow

Gems/Atom/Feature/Common/Assets/ShaderLib/Atom/Features/PBR/Lights/DiskLight.azsli

@@ -114,8 +114,13 @@ void ApplyDiskLight(ViewSrg::DiskLight light, Surface surface, inout LightingDat
         lightingData.diffuseLighting += GetDiffuseLighting(surface, lightingData, lightIntensity, posToLightDir) * litRatio;
 
         // Transmission contribution
-        lightingData.translucentBackLighting += GetBackLighting(surface, lightingData, lightIntensity, posToLightDir, transmissionDistance);
+        float3 backLighting = GetBackLighting(surface, lightingData, lightIntensity, posToLightDir, transmissionDistance);
         
+        // Attenuation applied to hide artifacts due to low-res shadow maps (might need some work in the future)
+        float attenuation = 1.0 / pow(max(1.0, sqrt(distanceToLight2)), lightingData.distanceAttenuation + 1.0);
+        
+        lightingData.translucentBackLighting += backLighting * attenuation;
+
         // Adjust the light direction for specular based on disk size
 
         // Calculate the reflection off the normal from the view direction

Gems/Atom/Feature/Common/Assets/ShaderLib/Atom/Features/PBR/Lights/PointLight.azsli

@@ -67,6 +67,7 @@ uint ComputeShadowIndex(const ViewSrg::PointLight light, const Surface surface)
 void ApplyPointLight(ViewSrg::PointLight light, Surface surface, inout LightingData lightingData)
 {
     float3 posToLight = light.m_position - surface.position;
+    float posToLightDist = length(posToLight);
     float d2 = dot(posToLight, posToLight); // light distance squared
     float falloff = d2 * light.m_invAttenuationRadiusSquared;
     
@@ -112,7 +113,12 @@ void ApplyPointLight(ViewSrg::PointLight light, Surface surface, inout LightingD
         lightingData.diffuseLighting += GetDiffuseLighting(surface, lightingData, lightIntensity, normalize(posToLight)) * litRatio;
 
         // Transmission contribution
-        lightingData.translucentBackLighting += GetBackLighting(surface, lightingData, lightIntensity, normalize(posToLight), transmissionDistance);
+        float3 backLighting = GetBackLighting(surface, lightingData, lightIntensity, normalize(posToLight), transmissionDistance);
+        
+        // Attenuation applied to hide artifacts due to low-res shadow maps (might need some work in the future)
+        float attenuation = 1.0 / pow(max(1.0, posToLightDist), lightingData.distanceAttenuation + 1.0);
+        
+        lightingData.translucentBackLighting += backLighting * attenuation;
 
         // Adjust the light direcion for specular based on bulb size