Rendering volumetric at quarter res

Data/Shaders/Vulkan/volumetric.frag

@@ -99,6 +99,10 @@ struct VolumetricConstant
     int CamViewID;
     int LightCount;
     float Ambient;
+    float Time;
+    float NoiseSpeed;
+    float NoiseScale;
+    float NoiseStrength;
 };
 
 [[vk::push_constant]]
@@ -135,6 +139,81 @@ float3 WorldPosFromDepth(float depth, float2 uv, float4x4 invProj, float4x4 invV
     return worldSpacePosition.xyz;
 }
 
+// Simplex 3D Noise 
+float mod289(float x) { return x - floor(x * (1.0 / 289.0)) * 289.0; }
+float3 mod289(float3 x) { return x - floor(x * (1.0 / 289.0)) * 289.0; }
+float4 mod289(float4 x) { return x - floor(x * (1.0 / 289.0)) * 289.0; }
+
+float4 permute(float4 x) { return mod289(((x*34.0)+1.0)*x); }
+
+float4 taylorInvSqrt(float4 r) { return 1.79284291400159 - 0.85373472095314 * r; }
+
+float snoise(float3 v)
+{
+    const float2  C = float2(1.0/6.0, 1.0/3.0) ;
+    const float4  D = float4(0.0, 0.5, 1.0, 2.0);
+
+    // First corner
+    float3 i  = floor(v + dot(v, C.yyy));
+    float3 x0 = v - i + dot(i, C.xxx);
+
+    // Other corners
+    float3 g = step(x0.yzx, x0.xyz);
+    float3 l = 1.0 - g;
+    float3 i1 = min(g.xyz, l.zxy);
+    float3 i2 = max(g.xyz, l.zxy);
+
+    // x0 = x0 - 0.0 + 0.0 * C.xxx;
+    float3 x1 = x0 - i1 + C.xxx;
+    float3 x2 = x0 - i2 + C.yyy;
+    float3 x3 = x0 - 1.0 + 3.0 * C.xxx;
+
+    // Permutations
+    i = mod289(i);
+    float4 p = permute(permute(permute(
+                i.z + float4(0.0, i1.z, i2.z, 1.0))
+              + i.y + float4(0.0, i1.y, i2.y, 1.0))
+              + i.x + float4(0.0, i1.x, i2.x, 1.0));
+
+    // Gradients: 7x7 points over a cube, mapped onto a unit sphere
+    float4 j = p - 49.0 * floor(p * (1.0 / 49.0));  // mod(p,7*7)
+
+    float4 x_ = floor(j * (1.0 / 7.0));
+    float4 y_ = floor(j - 7.0 * x_);  // mod(j,7)
+
+    float4 x = (x_ * 2.0 + 0.5) / 7.0 - 1.0;
+    float4 y = (y_ * 2.0 + 0.5) / 7.0 - 1.0;
+
+    float4 h = 1.0 - abs(x) - abs(y);
+
+    float4 b0 = float4(x.xy, y.xy);
+    float4 b1 = float4(x.zw, y.zw);
+
+    float4 s0 = floor(b0) * 2.0 + 1.0;
+    float4 s1 = floor(b1) * 2.0 + 1.0;
+    float4 sh = -step(h, 0.0);
+
+    float4 a0 = b0.xzyw + s0.xzyw * sh.xxyy;
+    float4 a1 = b1.xzyw + s1.xzyw * sh.zzww;
+
+    float3 g0 = float3(a0.xy, h.x);
+    float3 g1 = float3(a0.zw, h.y);
+    float3 g2 = float3(a1.xy, h.z);
+    float3 g3 = float3(a1.zw, h.w);
+
+    // Normalize gradients
+    float4 norm = taylorInvSqrt(float4(dot(g0,g0), dot(g1,g1), dot(g2,g2), dot(g3,g3)));
+    g0 *= norm.x;
+    g1 *= norm.y;
+    g2 *= norm.z;
+    g3 *= norm.w;
+
+    // Mix final noise value
+    float4 m = max(0.6 - float4(dot(x0,x0), dot(x1,x1), dot(x2,x2), dot(x3,x3)), 0.0);
+    m = m * m;
+    return 42.0 * dot(m*m, float4(dot(g0,x0), dot(g1,x1), dot(g2,x2), dot(g3,x3)));
+}
+
 PSOutput main(PSInput input)
 {
     CameraView camView = cameras[pushConstants.CamViewID];
@@ -180,17 +259,19 @@ PSOutput main(PSInput input)
             float currentDepth = projCoords.z;
             float closestDepth = textures[light.shadowMapTextureId[0]].Sample(mySampler, projCoords.xy).r;
 
+            float3 noiseOffset = float3(pushConstants.NoiseSpeed * pushConstants.Time, pushConstants.NoiseSpeed * pushConstants.Time, pushConstants.NoiseSpeed * pushConstants.Time);
+            float3 noiseSamplePos = (currentPosition + noiseOffset) * pushConstants.NoiseScale;
             if(closestDepth < currentDepth)
             {
-                accumFog += (ComputeScattering(dot(rayDirection, light.direction)).rrr * light.color) * pushConstants.Exponant;
+                accumFog += (ComputeScattering(dot(rayDirection, light.direction)).rrr * light.color) * pushConstants.Exponant * ((snoise(noiseSamplePos.xyz) + 1.0) / 2.0);
             }
             else
             {
-                accumFog += (ComputeScattering(dot(rayDirection, light.direction)).rrr * light.color) * pushConstants.Ambient;
+                accumFog += (ComputeScattering(dot(rayDirection, light.direction)).rrr * light.color) * pushConstants.Ambient * ((snoise(noiseSamplePos.xyz) + 1.0) / 2.0);
             }
         }
 
-        currentPosition += step;
+        currentPosition += step ;
         
     }
 

Data/Shaders/Vulkan/volumetric.vert

@@ -89,6 +89,10 @@ struct VolumetricConstant
     int CamViewID;
     int LightCount;
     float Ambient;
+    float Time;
+    float NoiseSpeed;
+    float NoiseScale;
+    float NoiseStrength;
 };
 
 [[vk::push_constant]]