Add absorption

lib/shader/material.glsl

@@ -156,7 +156,7 @@ void configure_material(const in uint matIdx, inout RenderState rs, out Material
   unpackMaterialTexInfo(matIdx, matTexInfo);
 
   vec4 albedo = evaluateMaterialTextureValue(matTexInfo.albedoTexture, uv);
-  c.albedo = matData.albedo * pow(albedo.xyz, vec3(2.2));
+  c.albedo = matData.albedo * to_linear_rgb(albedo.xyz);
 
   if (length(vertexColor) > 0.0) {
     c.albedo *= vertexColor.xyz;
@@ -226,12 +226,15 @@ void configure_material(const in uint matIdx, inout RenderState rs, out Material
   c.specular_f90 = vec3((1.0 - c.metallic) * c.specular + c.metallic);
 
   vec3 emission = evaluateMaterialTextureValue(matTexInfo.emissionTexture, uv).xyz;
-  c.emission = matData.emission * pow(emission, vec3(2.2));
+  c.emission = matData.emission * to_linear_rgb(emission);
 
   vec4 clearcoat = evaluateMaterialTextureValue(matTexInfo.clearcoatTexture, uv);
   c.clearcoat = matData.clearcoat * clearcoat.y;
   vec4 clearcoatRoughness = evaluateMaterialTextureValue(matTexInfo.clearcoatRoughnessTexture, uv);
   float clearcoat_alpha =
       matData.clearcoatRoughness * matData.clearcoatRoughness * clearcoatRoughness.x * clearcoatRoughness.x;
   c.clearcoat_alpha = max(clearcoat_alpha, MINIMUM_ROUGHNESS);
+
+  c.attenuationColor =  matData.attenuationColor;
+  c.attenuationDistance = matData.attenuationDistance;
 }

lib/shader/pt.frag

@@ -116,6 +116,8 @@ struct MaterialClosure {
   float clearcoat;
   float clearcoat_alpha;
   bool thin_walled;
+  float attenuationDistance;
+  vec3 attenuationColor;
   float ior;
   bool backside;
   vec3 n;
@@ -209,6 +211,13 @@ int sampleBSDFBounce(inout RenderState rs, inout vec3 pathWeight, out int eventT
     HitInfo hit;
     if (intersectScene_Nearest(r, hit)) {
       fillRenderState(r, hit, rs);
+
+      // Absorption
+      if(rs.closure.backside) {
+        vec3 absorptionCoefficient = -log(rs.closure.attenuationColor) / rs.closure.attenuationDistance;
+        pathWeight *= exp(-absorptionCoefficient*hit.tfar);
+      }
+
       return 1;
     }
   }
@@ -354,6 +363,7 @@ vec4 trace(const Ray r) {
         contrib += sampleIBL(rs.wo) * pathWeight;
         break;
       }
+
       // All clear. next sample has properly been generated and intersection was found.
       // Render state contains new intersection info.
       i++;

lib/shader/utils.glsl

@@ -218,3 +218,7 @@ ivec2 getStructParameterTexCoord(uint structIdx, uint paramIdx, uint structStrid
   return ivec2((structIdx * structStride + paramIdx) % MAX_TEXTURE_SIZE,
                (structIdx * structStride + paramIdx) / MAX_TEXTURE_SIZE);
 }
+
+vec3 to_linear_rgb(vec3 srgb) {
+  return pow(srgb.xyz, vec3(2.2));
+}