Move directional shadow coordinates computation to PS + Fix clamp values

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

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

@@ -92,7 +92,6 @@ struct VSOutput
     float3 m_bitangent : BITANGENT; 
     float3 m_worldPosition : UV0;
     float3 m_shadowCoords[ViewSrg::MaxCascadeCount] : UV4;
-    float3 m_shrinkedShadowCoords[ViewSrg::MaxCascadeCount] : UV9;
 
     // Extended fields (only referenced in this azsl file)...
     float2 m_uv[UvSetCount] : UV1;
@@ -137,14 +136,6 @@ VSOutput SkinVS(VSInput IN)
     }
 
     VertexHelper(IN, OUT, worldPosition, false);
-
-    // Fetch shadow coords for shrinked world position (used in thin transmission materials) 
-    const uint shadowIndex = ViewSrg::m_shadowIndexDirectionalLight;
-    DirectionalLightShadow::GetShadowCoords(
-        shadowIndex,
-        worldPosition - MaterialSrg::m_shrinkFactor * OUT.m_normal,
-        OUT.m_normal,
-        OUT.m_shrinkedShadowCoords);
         
     return OUT;
 }
@@ -345,15 +336,19 @@ PbrLightingOutput SkinPS_Common(VSOutput IN)
     
     // Directional light shadow coordinates
     lightingData.shadowCoords = IN.m_shadowCoords;
-    lightingData.shrinkedShadowCoords = IN.m_shrinkedShadowCoords;
 
     // Diffuse and Specular response (used in IBL calculations)
     lightingData.specularResponse = FresnelSchlickWithRoughness(lightingData.NdotV, surface.specularF0, surface.roughnessLinear);
     lightingData.diffuseResponse = 1.0 - lightingData.specularResponse;
 
+    // ------- Thin Object Light Transmission -------
+
     // Angle offset for subsurface scattering through thin objects
     lightingData.angleOffset = MaterialSrg::m_angleOffset;
 
+    // Shrink (absolute) offset towards the normal opposite direction to ensure correct shadow map projection
+    lightingData.shrinkFactor = MaterialSrg::m_shrinkFactor;
+
     // ------- 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/ShaderLib/Atom/Features/PBR/BackLighting.azsli

@@ -65,7 +65,7 @@ float3 GetBackLighting(Surface surface, LightingData lightingData, float3 lightI
             {
                 // Irradiance arround surface point. 
                 // Begin the transmittance dot product slightly before it would with the regular dot(N,L)
-                float E = saturate(lightingData.angleOffset + dot(-surface.normal, dirToLight));
+                float E = max(lightingData.angleOffset + dot(-surface.normal, dirToLight),0.0);
 
                 // Transmission distance computed from shadowmaps modulated by editor-exposed parameters
                 float s = transmissionDistance * surface.transmission.thickness * (100 - transmissionParams.w) * 10;

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

@@ -33,6 +33,9 @@ class LightingData
 
     // Angle to accept below (N . L = 0) in scattering through thin objects
     float angleOffset; 
+    
+    // Shrink (absolute) offset towards the normal opposite direction to ensure correct shadow map projection
+    float shrinkFactor;
 
     // Normalized direction from surface to camera
     float3 dirToCamera;

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

@@ -29,6 +29,14 @@ void ApplyDirectionalLights(Surface surface, inout LightingData lightingData)
             lightingData.shadowCoords,
             surface.vertexNormal,
             debugInfo);
+
+        // Fetch shadow coords for shrinked world position (used in thin transmission materials) 
+        float3 shrinkedShadowCoords[ViewSrg::MaxCascadeCount];
+        DirectionalLightShadow::GetShadowCoords(
+            shadowIndex,
+            surface.position - lightingData.shrinkFactor * surface.normal,
+            surface.normal,
+            lightingData.shrinkedShadowCoords);
             
         if (o_transmission_mode == TransmissionMode::ThickObject)
         {