PBR Renderer: use special value to pack zero-length normals

Author: TheMostDiligent

Hydrogent/src/HnMeshUtils.cpp

@@ -411,7 +411,12 @@ pxr::VtValue HnMeshUtils::PackVertexNormals(const pxr::VtValue& Normals) const
     Uint32*                  pPackedNormals = reinterpret_cast<Uint32*>(PackedNormals.data());
     for (size_t i = 0; i < NormalsArray.size(); ++i)
     {
-        pPackedNormals[i] = PBR_Renderer::PackVertexNormal(normalize(ToFloat3(NormalsArray[i])));
+        float3 Normal = ToFloat3(NormalsArray[i]);
+        float  Length = length(Normal);
+        if (Length != 0)
+            Normal /= Length;
+
+        pPackedNormals[i] = PBR_Renderer::PackVertexNormal(Normal);
     }
     return pxr::VtValue::Take(PackedNormals);
 }

PBR/interface/PBR_Renderer.hpp

@@ -938,6 +938,9 @@ inline void PBR_Renderer::ProcessTexturAttribs(PBR_Renderer::PSO_FLAGS PSOFlags,
 
 inline Uint32 PBR_Renderer::PackVertexNormal(const float3& Normal)
 {
+    if (Normal == float3{})
+        return ~0u;
+
     Uint32 x = static_cast<Uint32>(clamp((Normal.x + 1.f) * 32767.f, 0.f, 65535.f));
     Uint32 y = static_cast<Uint32>(clamp((Normal.y + 1.f) * 16383.f, 0.f, 32767.f));
     Uint32 z = Normal.z >= 0 ? 0 : 1;

Shaders/PBR/private/RenderPBR.vsh

@@ -107,11 +107,14 @@ float4 GetVertexColor(float4 Color)
 // Reverse of PBR_Renderer::PackVertexNormal()
 float3 GetNormal(in uint PackedNormal)
 {
-    float3 Normal;
-    Normal.x = float( PackedNormal         & 0xFFFFu) / 32767.0 - 1.0;
-    Normal.y = float((PackedNormal >> 16u) & 0x7FFFu) / 16383.0 - 1.0;
-    Normal.z = sqrt(max(1.0 - dot(Normal.xy, Normal.xy), 0.0));
-    Normal.z *= (PackedNormal & 0x80000000u) != 0u ? -1.0 : 1.0;
+    float3 Normal = float3(0.0, 0.0, 0.0);
+    if (PackedNormal != 0xFFFFFFFFu)
+    {
+        Normal.x = float( PackedNormal         & 0xFFFFu) / 32767.0 - 1.0;
+        Normal.y = float((PackedNormal >> 16u) & 0x7FFFu) / 16383.0 - 1.0;
+        Normal.z = sqrt(max(1.0 - dot(Normal.xy, Normal.xy), 0.0));
+        Normal.z *= (PackedNormal & 0x80000000u) != 0u ? -1.0 : 1.0;
+    }
     return Normal;
 }
 #else