Pack normal on 1212bit in 888

ScriptableRenderPipeline/Core/CoreRP/ShaderLibrary/Packing.hlsl

     return PackShort(cb);
 }
 
+// Pack float2 (each of 12 bit) in 888
+real3 PackFloat2To888(real2 f)
+{
+    uint2 i = (uint2)(f * 4095.0);
+    uint2 hi = i >> 8;
+    uint2 lo = i & 255;
+    // 8 bit in lo, 4 bit in hi
+    uint3 cb = uint3(lo, hi.x | (hi.y << 4));
+
+    return cb / 255.0;
+}
+
+// Unpack 2 float of 12bit packed into a 888
+real2 Unpack888ToFloat2(real3 x)
+{
+    uint3 i = (uint3)(x * 255.0);
+    // 8 bit in lo, 4 bit in hi
+    uint hi = i.z >> 4;
+    uint lo = i.z & 15;
+    uint2 cb = i.xy | uint2(lo << 8, hi << 8);
+
+    return cb / 4095.0;
+}
 #endif // SHADER_API_GLES
 
 #endif // UNITY_PACKING_INCLUDED

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/Lit.cs

 
         public override int GetMaterialGBufferCount() { return (int)GBufferMaterial.Count; }
 
-        RenderTextureFormat[] m_RTFormat4 = { RenderTextureFormat.ARGB32, RenderTextureFormat.ARGB2101010, RenderTextureFormat.ARGB32, RenderTextureFormat.RGB111110Float };
+        RenderTextureFormat[] m_RTFormat4 = { RenderTextureFormat.ARGB32, RenderTextureFormat.ARGB32, RenderTextureFormat.ARGB32, RenderTextureFormat.RGB111110Float };
         RenderTextureReadWrite[] m_RTReadWrite4 = { RenderTextureReadWrite.sRGB, RenderTextureReadWrite.Linear, RenderTextureReadWrite.Linear, RenderTextureReadWrite.Linear };
 
         public override void GetMaterialGBufferDescription(out RenderTextureFormat[] RTFormat, out RenderTextureReadWrite[] RTReadWrite)

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/Lit.hlsl

     // Warning: the contents are later overwritten for Standard and SSS!
     outGBuffer0 = float4(surfaceData.baseColor, surfaceData.specularOcclusion);
 
-    // RT1 - 10:10:10:2
+    // RT1 - 8:8:8:8
+    // Our tangent encoding is based on our normal.
+    // With octahedral quad packing we get an artifact for reconstructed tangent at the center of this quad. We use rect packing instead to avoid it.
-    // To have better precision encode the sign of XY separately.
-    uint octNormalSign = (octNormalWS.x < 0.0 ? 1 : 0) | (octNormalWS.y < 0.0 ? 2 : 0);
+    float3 packNormalWS = PackFloat2To888(saturate(octNormalWS * 0.5 + 0.5));
-    outGBuffer1 = float4(PerceptualSmoothnessToPerceptualRoughness(surfaceData.perceptualSmoothness), abs(octNormalWS), PackInt(octNormalSign, 2));
+    outGBuffer1 = float4(packNormalWS, PerceptualSmoothnessToPerceptualRoughness(surfaceData.perceptualSmoothness));
 
     // RT2 - 8:8:8:8
     uint materialFeatureId;
     float3 baseColor = inGBuffer0.rgb;
 
     bsdfData.specularOcclusion   = inGBuffer0.a; // Later possibly overwritten by SSS
-    bsdfData.perceptualRoughness = inGBuffer1.r;
-
-    float2 octNormalWS = inGBuffer1.gb;
-    uint octNormalSign = UnpackInt(inGBuffer1.a, 2);
-
-    octNormalWS.x = (octNormalSign & 1) ? -octNormalWS.x : octNormalWS.x;
-    octNormalWS.y = (octNormalSign & 2) ? -octNormalWS.y : octNormalWS.y;
+    bsdfData.perceptualRoughness = inGBuffer1.a;
-    bsdfData.normalWS = UnpackNormalOctRectEncode(octNormalWS);
+    float3 packNormalWS = inGBuffer1.rgb;
+    float2 octNormalWS = Unpack888ToFloat2(packNormalWS);
+    bsdfData.normalWS = UnpackNormalOctRectEncode(octNormalWS * 2.0 - 1.0);
 
     bakeDiffuseLighting = inGBuffer3.rgb;