PBR Shading: fixed normal computation from gradients for left-handed …

…coordinate systems
DiligentGraphics · Jan 19, 2024 · 13f8321 · 13f8321
1 parent da3c592
commit 13f8321
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Showing 4 changed files with 20 additions and 16 deletions.
diff --git a/Hydrogent/src/Tasks/HnBeginFrameTask.cpp b/Hydrogent/src/Tasks/HnBeginFrameTask.cpp
@@ -290,6 +290,7 @@ void HnBeginFrameTask::UpdateFrameConstants(IDeviceContext* pCtx, IBuffer* pFram
                 1.f / static_cast<float>(m_FrameBufferWidth),
                 1.f / static_cast<float>(m_FrameBufferHeight),
             };
+            CamAttribs.fHandness = ViewMatrix.Determinant() > 0 ? 1.f : -1.f;
 
             CamAttribs.mViewT        = ViewMatrix.Transpose();
             CamAttribs.mProjT        = ProjMatrix.Transpose();

diff --git a/Shaders/Common/public/BasicStructures.fxh b/Shaders/Common/public/BasicStructures.fxh
@@ -118,10 +118,11 @@ struct CameraAttribs
     float4 f4Position;     // Camera world position
     float4 f4ViewportSize; // (width, height, 1/width, 1/height)
 
-    float2 f2ViewportOrigin; // (min x, min y)
     float fNearPlaneZ; 
-    float fFarPlaneZ; // fNearPlaneZ < fFarPlaneZ
-
+    float fFarPlaneZ;  // fNearPlaneZ < fFarPlaneZ
+    float fHandness;   // +1.0 for right-handed coordinate system, -1.0 for left-handed
+    float Padding;
+
 #ifdef __cplusplus
     float4x4 mViewT;
     float4x4 mProjT;

diff --git a/Shaders/PBR/private/RenderPBR.psh b/Shaders/PBR/private/RenderPBR.psh
@@ -318,7 +318,7 @@ PSOutput main(in VSOutput VSOut,
     float3 MeshNormal = float3(0.0, 0.0, 0.0);
 #endif
     // We have to compute gradients in uniform flow control to avoid issues with perturbed normal
-    PerturbNormalInfo NormalInfo = GetPerturbNormalInfo(VSOut.WorldPos, MeshNormal, IsFrontFace);
+    PerturbNormalInfo NormalInfo = GetPerturbNormalInfo(VSOut.WorldPos, MeshNormal, IsFrontFace, g_Frame.Camera.fHandness);
 
     PBRMaterialTextureAttribs NormalTexAttribs;
 #   if USE_NORMAL_MAP

diff --git a/Shaders/PBR/public/PBR_Shading.fxh b/Shaders/PBR/public/PBR_Shading.fxh
@@ -119,26 +119,28 @@ struct PerturbNormalInfo
     float3 dPos_dx;
     float3 dPos_dy;
     float3 Normal;
-    bool   IsFrontFace;
+    float  Face; // +1.0 if front face, -1.0 if back face
 };
 
-PerturbNormalInfo GetPerturbNormalInfo(in float3 Pos, in float3 Normal, in bool IsFrontFace)
+PerturbNormalInfo GetPerturbNormalInfo(in float3 Pos,           // World position
+                                       in float3 Normal,        // Mesh normal
+                                       in bool   IsFrontFace,   // True if front face
+                                       in float  CameraHandness // 1.0 if right-handed, -1.0 if left-handed
+                                      )
 {
     PerturbNormalInfo Info;
     Info.dPos_dx = ddx(Pos);
     Info.dPos_dy = ddy(Pos);
-
-    Info.IsFrontFace = IsFrontFace;
+    Info.Face    = IsFrontFace ? +1.0 : -1.0;
 
     float NormalLen = length(Normal);
     if (NormalLen > 1e-5)
     {
-        NormalLen *= IsFrontFace ? +1.0 : -1.0;
-        Info.Normal = Normal / NormalLen;
+        Info.Normal = Normal / (NormalLen * Info.Face);
     }
     else
     {
-        Info.Normal = normalize(cross(Info.dPos_dx, Info.dPos_dy));
+        Info.Normal = normalize(cross(Info.dPos_dx, Info.dPos_dy)) * CameraHandness;
 #if (defined(GLSL) || defined(GL_ES)) && !defined(VULKAN)
         // In OpenGL, the screen is upside-down, so we have to invert the vector
         Info.Normal *= -1.0;
@@ -153,14 +155,14 @@ PerturbNormalInfo GetPerturbNormalInfo(in float3 Pos, in float3 Normal, in bool
 // Find the normal for this fragment, pulling either from a predefined normal map
 // or from the interpolated mesh normal and tangent attributes.
 float3 PerturbNormal(PerturbNormalInfo NormalInfo,
-                     in float2 dUV_dx,
-                     in float2 dUV_dy,
-                     in float3 TSNormal,
-                     bool      HasUV)
+                     in float2         dUV_dx,
+                     in float2         dUV_dy,
+                     in float3         TSNormal,
+                     bool              HasUV)
 {
     if (HasUV)
     {
-        TSNormal.xy *= NormalInfo.IsFrontFace ? +1.0 : -1.0;
+        TSNormal.xy *= NormalInfo.Face;
         return TransformTangentSpaceNormalGrad(NormalInfo.dPos_dx, NormalInfo.dPos_dy, dUV_dx, dUV_dy, NormalInfo.Normal, TSNormal);
     }
     else