Add explanations for default constant parameters + define as separate const variables (https://github.com/o3de/o3de/pull/6428#discussion_r776073076, https://github.com/o3de/o3de/pull/6428#discussion_r776072881, https://github.com/o3de/o3de/pull/6428#discussion_r776069391)

Signed-off-by: Santi Paprika <santi.gonzalez.cs@gmail.com>
2022-01-04 12:23:02 +01:00
parent c814be22fd
commit 69df812941
7 changed files with 45 additions and 14 deletions
@@ -75,8 +75,9 @@ float3 GetBackLighting(Surface surface, LightingData lightingData, float3 lightI
                // Increase angle of influence (angle(N,L) -> angle(N,L) + acos(transmissionNdLBias)) to smooth transition regions
                float3 E = surface.albedo * saturate(lightingData.transmissionNdLBias + dot(-surface.normal, dirToLight));

-                // Transmission distance modulated by hardcoded constant (could be exposed as a weight of scattering distance for transmission)
-                float s = transmissionDistance * 100.0;
+                // Transmission distance modulated by hardcoded constant C (could be exposed as a weight of scattering distance for transmission)
+                const float C = 100.0f;
+                float s = transmissionDistance * C;
                
                // Use scattering color to weight thin object transmission color
                const float3 invScattering = rcp(transmissionParams.xyz);
@@ -135,8 +135,15 @@ void ApplyCapsuleLight(ViewSrg::CapsuleLight light, Surface surface, inout Light
        float3 closestIntersectionPoint = startPoint + closestT * startToEnd;
        float3 posToLight = closestIntersectionPoint - surface.position;

-        // Tranmission contribution
-        lightingData.translucentBackLighting += GetBackLighting(surface, lightingData, lightIntensity, normalize(posToLight), -1.0f, 0.0f);
+        // Transmission contribution
+        // We cannot compute the actual transmission distance so we want to:
+        // - If transmission mode is thick object -> use transmission thickness parameter instead
+        // - If transmission mode is thin object -> ignore back lighting
+        // To detect and apply this behavior in the GetBackLighting function, we need to use a negative transmissionDistance 
+        const float transmissionDistance = -1.0f;
+        // If the transmissionDistance is ignored then the attenuation distance (only used on thin objects) does not have any influence
+        const float attenuationDistance = 0.0f;
+        lightingData.translucentBackLighting += GetBackLighting(surface, lightingData, lightIntensity, normalize(posToLight), transmissionDistance, attenuationDistance);

        // Calculate the offset from the nearest point on the reflection vector to the nearest point on the capsule light
        float3 posToClosestPointAlongReflection = dot(posToLight, reflectionDir) * reflectionDir;
@@ -20,7 +20,9 @@ void ApplyDirectionalLights(Surface surface, inout LightingData lightingData)
    float litRatio = 1.0f;
    float camToSurfDist = distance(ViewSrg::m_worldPosition, surface.position);

-    // Distance travelled by the light inside the object. If not redefined, it will take mode-specific null behaviors (see GetBackLighting())
+    // Distance travelled by the light inside the object. If not redefined to a non-negative value, it will take the following behavior:
+    // - If transmission mode is thick object -> use transmission thickness parameter instead
+    // - If transmission mode is thin object -> ignore back lighting
    float transmissionDistance = -1.0f;

    if (o_enableShadows && shadowIndex <  SceneSrg::m_directionalLightCount)
@@ -77,8 +77,9 @@ void ApplyDiskLight(ViewSrg::DiskLight light, Surface surface, inout LightingDat
        // shadow
        float litRatio = 1.0;

-
-        // Distance travelled by the light inside the object. If not redefined, it will take mode-specific null behaviors (see GetBackLighting())
+        // Distance travelled by the light inside the object. If not redefined to a non-negative value, it will take the following behavior:
+        // - If transmission mode is thick object -> use transmission thickness parameter instead
+        // - If transmission mode is thin object -> ignore back lighting
        float transmissionDistance = -1.0f;

        if (o_enableShadows)
@@ -49,6 +49,16 @@ void AddSampleContribution(
    float3 intensityRgb = float3(intensity, intensity, intensity);

    diffuseAcc += GetDiffuseLighting(surface, lightingData, intensityRgb, posToLightSampleDir);
-    translucentAcc += GetBackLighting(surface, lightingData, intensityRgb, posToLightSampleDir, -1.0f, 0.0f);
+
+    // Transmission contribution
+    // We cannot compute the actual transmission distance so we want to:
+    // - If transmission mode is thick object -> use transmission thickness parameter instead
+    // - If transmission mode is thin object -> ignore back lighting
+    // To detect and apply this behavior in the GetBackLighting function, we need to use a negative transmissionDistance 
+    const float transmissionDistance = -1.0f;
+    // If the transmissionDistance is ignored then the attenuation distance (only used on thin objects) does not have any influence
+    const float attenuationDistance = 0.0f;
+    translucentAcc += GetBackLighting(surface, lightingData, intensityRgb, posToLightSampleDir, transmissionDistance, attenuationDistance);
+
    specularAcc += GetSpecularLighting(surface, lightingData, intensityRgb, posToLightSampleDir);
 }
@@ -85,7 +85,9 @@ void ApplyPointLight(ViewSrg::PointLight light, Surface surface, inout LightingD
        // shadow
        float litRatio = 1.0;

-        // Distance travelled by the light inside the object. If not redefined, it will take mode-specific null behaviors (see GetBackLighting())
+        // Distance travelled by the light inside the object. If not redefined to a non-negative value, it will take the following behavior:
+        // - If transmission mode is thick object -> use transmission thickness parameter instead
+        // - If transmission mode is thin object -> ignore back lighting
        float transmissionDistance = -1.0f;

        if (o_enableShadows)
@@ -148,13 +148,21 @@ void ApplyQuadLight(ViewSrg::QuadLight light, Surface surface, inout LightingDat
                GetDiffuseLighting(surface, lightingData, intensity, dirToLightCenter)
            );
            
+            // Transmission contribution
+            // We cannot compute the actual transmission distance so we want to:
+            // - If transmission mode is thick object -> use transmission thickness parameter instead
+            // - If transmission mode is thin object -> ignore back lighting
+            // To detect and apply this behavior in the GetBackLighting function, we need to use a negative transmissionDistance 
+            const float transmissionDistance = -1.0f;
+            // If the transmissionDistance is ignored then the attenuation distance (only used on thin objects) does not have any influence
+            const float attenuationDistance = 0.0f;
            lightingData.translucentBackLighting +=
            (
-                GetBackLighting(surface, lightingData, intensity, p0, -1.0f, 0.0f) +
-                GetBackLighting(surface, lightingData, intensity, p1, -1.0f, 0.0f) +
-                GetBackLighting(surface, lightingData, intensity, p2, -1.0f, 0.0f) +
-                GetBackLighting(surface, lightingData, intensity, p3, -1.0f, 0.0f) +
-                GetBackLighting(surface, lightingData, intensity, dirToLightCenter, -1.0f, 0.0f)
+                GetBackLighting(surface, lightingData, intensity, p0, transmissionDistance, attenuationDistance) +
+                GetBackLighting(surface, lightingData, intensity, p1, transmissionDistance, attenuationDistance) +
+                GetBackLighting(surface, lightingData, intensity, p2, transmissionDistance, attenuationDistance) +
+                GetBackLighting(surface, lightingData, intensity, p3, transmissionDistance, attenuationDistance) +
+                GetBackLighting(surface, lightingData, intensity, dirToLightCenter, transmissionDistance, attenuationDistance)
            );
            
            // Calculate specular by choosing a single representative point on the light's surface based on the reflection ray