diff --git a/Res/Shader/volume.hlsl b/Res/Shader/volume.hlsl
index 9c156d50..e2f05418 100644
--- a/Res/Shader/volume.hlsl
+++ b/Res/Shader/volume.hlsl
@@ -85,6 +85,11 @@ bool get_hdda_hit(inout pnanovdb_readaccessor_t acc, inout float tmin, float3 or
     return hit;
 }
 
+float phase_function()
+{
+    return 1.0;
+}
+
 PSInput MainVS(VSInput input)
 {
     PSInput output;
@@ -167,9 +172,12 @@ float4 MainPS(PSInput input) : SV_TARGET
             continue;
         }
         
-        float3 S = density * float3(1, 1, 1);
-        color += transmittance * S * _StepSize;
-        transmittance *= exp(-density * _StepSize);
+        float sigmaS = density;
+        float sigmaE = max(0.000001, sigmaS);
+        float3 S = sigmaS * phase_function() * float3(1, 1, 1);
+        float3 Sint = (S - S * exp(-sigmaE * _StepSize)) / sigmaE;
+        color += transmittance * Sint;
+        transmittance *= exp(-sigmaE * _StepSize);
         
         tmin += _StepSize;
     }