SL-18095 WIP -- Add Mikktspace tangent generation for PBR materials and switch to per-pixel binormal generation. Still bugged with some test content.

8 files changed, 337 insertions, 68 deletions

diff --git a/autobuild.xml b/autobuild.xml
index bf20cb788e..e984551455 100644
--- a/autobuild.xml
+++ b/autobuild.xml
@@ -1836,6 +1836,50 @@
         <key>version</key>
         <string>0.16.561408</string>
       </map>
+      <key>mikktspace</key>
+      <map>
+        <key>canonical_repo</key>
+        <string>https://bitbucket.org/lindenlab/3p-mikktspace</string>
+        <key>copyright</key>
+        <string>Copyright (C) 2011 by Morten S. Mikkelsen</string>
+        <key>description</key>
+        <string>Mikktspace Tangent Generator</string>
+        <key>license</key>
+        <string>Copyright (C) 2011 by Morten S. Mikkelsen</string>
+        <key>license_file</key>
+        <string>mikktspace.txt</string>
+        <key>name</key>
+        <string>mikktspace</string>
+        <key>platforms</key>
+        <map>
+          <key>darwin64</key>
+          <map>
+            <key>archive</key>
+            <map>
+              <key>hash</key>
+              <string>b48b7ac0792d3ea8f087d99d9e4a29d8</string>
+              <key>url</key>
+              <string>https://automated-builds-secondlife-com.s3.amazonaws.com/ct2/104415/914944/mikktspace-1-darwin64-574859.tar.bz2</string>
+            </map>
+            <key>name</key>
+            <string>darwin64</string>
+          </map>
+          <key>windows64</key>
+          <map>
+            <key>archive</key>
+            <map>
+              <key>hash</key>
+              <string>02e9e5b6fe6788f4d2babb83ec544843</string>
+              <key>url</key>
+              <string>https://automated-builds-secondlife-com.s3.amazonaws.com/ct2/104406/914909/mikktspace-1-windows64-574859.tar.bz2</string>
+            </map>
+            <key>name</key>
+            <string>windows64</string>
+          </map>
+        </map>
+        <key>version</key>
+        <string>1</string>
+      </map>
       <key>minizip-ng</key>
       <map>
         <key>canonical_repo</key>
diff --git a/indra/cmake/LLMath.cmake b/indra/cmake/LLMath.cmake
index 893920ae6f..3cbb7ad561 100644
--- a/indra/cmake/LLMath.cmake
+++ b/indra/cmake/LLMath.cmake
@@ -1,5 +1,8 @@
 # -*- cmake -*-
 
+include(Variables)
+include(Mikktspace)
+
 set(LLMATH_INCLUDE_DIRS
     ${LIBS_OPEN_DIR}/llmath
     )
diff --git a/indra/llmath/llvolume.cpp b/indra/llmath/llvolume.cpp
index 4a069b0f63..539db9d0e1 100644
--- a/indra/llmath/llvolume.cpp
+++ b/indra/llmath/llvolume.cpp
@@ -32,6 +32,7 @@
 #include <stdint.h>
 #endif
 #include <cmath>
+#include <unordered_map>
 
 #include "llerror.h"
 
@@ -52,6 +53,9 @@
 #include "llmeshoptimizer.h"
 #include "lltimer.h"
 
+#include "mikktspace/mikktspace.h"
+#include "mikktspace/mikktspace.c" // insert mikktspace implementation into llvolume object file
+
 #define DEBUG_SILHOUETTE_BINORMALS 0
 #define DEBUG_SILHOUETTE_NORMALS 0 // TomY: Use this to display normals using the silhouette
 #define DEBUG_SILHOUETTE_EDGE_MAP 0 // DaveP: Use this to display edge map using the silhouette
@@ -2096,9 +2100,9 @@ void LLVolume::regen()
 	createVolumeFaces();
 }
 
-void LLVolume::genTangents(S32 face)
+void LLVolume::genTangents(S32 face, bool mikktspace)
 {
-	mVolumeFaces[face].createTangents();
+	mVolumeFaces[face].createTangents(mikktspace);
 }
 
 LLVolume::~LLVolume()
@@ -4797,6 +4801,17 @@ LLVolumeFace& LLVolumeFace::operator=(const LLVolumeFace& src)
 			mTangents = NULL;
 		}
 
+        if (src.mMikktSpaceTangents)
+        {
+            allocateTangents(src.mNumVertices, true);
+            LLVector4a::memcpyNonAliased16((F32*)mMikktSpaceTangents, (F32*)src.mMikktSpaceTangents, vert_size);
+        }
+        else
+        {
+            ll_aligned_free_16(mMikktSpaceTangents);
+            mMikktSpaceTangents = nullptr;
+        }
+
 		if (src.mWeights)
 		{
             llassert(!mWeights); // don't orphan an old alloc here accidentally
@@ -4867,6 +4882,8 @@ void LLVolumeFace::freeData()
 	mIndices = NULL;
 	ll_aligned_free_16(mTangents);
 	mTangents = NULL;
+    ll_aligned_free_16(mMikktSpaceTangents);
+    mMikktSpaceTangents = nullptr;
 	ll_aligned_free_16(mWeights);
 	mWeights = NULL;
 
@@ -4988,6 +5005,9 @@ void LLVolumeFace::remap()
     ll_aligned_free_16(mTangents);
     mTangents = NULL;
 
+    ll_aligned_free_16(mMikktSpaceTangents);
+    mMikktSpaceTangents = nullptr;
+
     // Assign new values
     mIndices = remap_indices;
     mPositions = remap_positions;
@@ -5514,6 +5534,12 @@ bool LLVolumeFace::cacheOptimize()
 		}
 	}
 
+    llassert(mTangents == nullptr); // cache optimize called too late, tangents already generated
+    llassert(mMikktSpaceTangents == nullptr);
+
+    // =====================================================================================
+    // DEPRECATED -- cacheOptimize should always be called before tangents are generated
+    // =====================================================================================
 	LLVector4a* binorm = NULL;
 	if (mTangents)
 	{
@@ -5526,11 +5552,11 @@ bool LLVolumeFace::cacheOptimize()
 			return false;
 		}
 	}
+    // =====================================================================================
 
-	//allocate mapping of old indices to new indices
+    //allocate mapping of old indices to new indices
 	std::vector<S32> new_idx;
-
-	try
+    try
 	{
 		new_idx.resize(mNumVertices, -1);
 	}
@@ -5673,6 +5699,7 @@ void LLVolumeFace::swapData(LLVolumeFace& rhs)
 	llswap(rhs.mPositions, mPositions);
 	llswap(rhs.mNormals, mNormals);
 	llswap(rhs.mTangents, mTangents);
+    llswap(rhs.mMikktSpaceTangents, mMikktSpaceTangents);
 	llswap(rhs.mTexCoords, mTexCoords);
 	llswap(rhs.mIndices,mIndices);
 	llswap(rhs.mNumVertices, mNumVertices);
@@ -6380,37 +6407,217 @@ BOOL LLVolumeFace::createCap(LLVolume* volume, BOOL partial_build)
 void CalculateTangentArray(U32 vertexCount, const LLVector4a *vertex, const LLVector4a *normal,
         const LLVector2 *texcoord, U32 triangleCount, const U16* index_array, LLVector4a *tangent);
 
-void LLVolumeFace::createTangents()
+
+// data structures for tangent generation
+
+// key for summing tangents
+// We will blend tangents wherever a common position and normal is found
+struct MikktKey
 {
-	LL_PROFILE_ZONE_SCOPED_CATEGORY_VOLUME
+    // Position
+    LLVector3 p;
+    // Normal
+    LLVector3 n;
 
-	if (!mTangents)
-	{
-		allocateTangents(mNumVertices);
+    bool operator==(const MikktKey& rhs) const { return p == rhs.p && n == rhs.n; }
+};
 
-		//generate tangents
-		//LLVector4a* pos = mPositions;
-		//LLVector2* tc = (LLVector2*) mTexCoords;
-		LLVector4a* binorm = (LLVector4a*) mTangents;
+// sum of tangents and list of signs and index array indices for a given position and normal combination
+// sign must be kept separate from summed tangent because a single position and normal may have a different
+// tangent facing where UV seams exist
+struct MikktTangent
+{
+    // tangent vector
+    LLVector3 t;
+    // signs
+    std::vector<F32> s;
+    // indices (in index array)
+    std::vector<S32> i;
+};
 
-		LLVector4a* end = mTangents+mNumVertices;
-		while (binorm < end)
-		{
-			(*binorm++).clear();
-		}
+// hash function for MikktTangent
+namespace boost
+{
+    template <>
+    struct hash<LLVector3>
+    {
+        std::size_t operator()(LLVector3 const& k) const
+        {
+            size_t seed = 0;
+            boost::hash_combine(seed, k.mV[0]);
+            boost::hash_combine(seed, k.mV[1]);
+            boost::hash_combine(seed, k.mV[2]);
+            return seed;
+        }
+    };
+
+    template <>
+    struct hash<MikktKey>
+    {
+        std::size_t operator()(MikktKey const& k) const
+        {
+            size_t seed = 0;
+            boost::hash_combine(seed, k.p);
+            boost::hash_combine(seed, k.n);
+            return seed;
+        }
+    };
+}
+
+// boost adapter
+namespace std
+{
+    template<>
+    struct hash<MikktKey>
+    {
+        std::size_t operator()(MikktKey const& k) const
+        {
+            return boost::hash<MikktKey>()(k);
+        }
+    };
+}
+
+struct MikktData
+{
+    LLVolumeFace* face;
+    std::unordered_map<MikktKey, MikktTangent > tangents;
+};
 
-		binorm = mTangents;
 
-		CalculateTangentArray(mNumVertices, mPositions, mNormals, mTexCoords, mNumIndices/3, mIndices, mTangents);
+void LLVolumeFace::createTangents(bool mikktspace)
+{
+    LL_PROFILE_ZONE_SCOPED_CATEGORY_VOLUME;
 
-		//normalize tangents
-		for (U32 i = 0; i < mNumVertices; i++) 
-		{
-			//binorm[i].normalize3fast();
-			//bump map/planar projection code requires normals to be normalized
-			mNormals[i].normalize3fast();
-		}
-	}
+    auto& tangents = mikktspace ? mMikktSpaceTangents : mTangents;
+
+    if (!tangents)
+    {
+        allocateTangents(mNumVertices, mikktspace);
+
+        if (mikktspace)
+        {
+            LL_PROFILE_ZONE_NAMED_CATEGORY_VOLUME("mikktspace");
+            SMikkTSpaceInterface ms;
+
+            ms.m_getNumFaces = [](const SMikkTSpaceContext* pContext)
+            {
+                MikktData* data = (MikktData*)pContext->m_pUserData;
+                LLVolumeFace* face = data->face;
+                return face->mNumIndices / 3;
+            };
+
+            ms.m_getNumVerticesOfFace = [](const SMikkTSpaceContext* pContext, const int iFace)
+            {
+                return 3;
+            };
+
+            ms.m_getPosition = [](const SMikkTSpaceContext* pContext, float fvPosOut[], const int iFace, const int iVert)
+            {
+                MikktData* data = (MikktData*)pContext->m_pUserData;
+                LLVolumeFace* face = data->face;
+                S32 idx = face->mIndices[iFace * 3 + iVert];
+                auto& vert = face->mPositions[idx];
+                F32* v = vert.getF32ptr();
+                fvPosOut[0] = v[0];
+                fvPosOut[1] = v[1];
+                fvPosOut[2] = v[2];
+            };
+
+            ms.m_getNormal = [](const SMikkTSpaceContext* pContext, float fvNormOut[], const int iFace, const int iVert)
+            {
+                MikktData* data = (MikktData*)pContext->m_pUserData;
+                LLVolumeFace* face = data->face;
+                S32 idx = face->mIndices[iFace * 3 + iVert];
+                auto& norm = face->mNormals[idx];
+                F32* n = norm.getF32ptr();
+                fvNormOut[0] = n[0];
+                fvNormOut[1] = n[1];
+                fvNormOut[2] = n[2];
+            };
+
+            ms.m_getTexCoord = [](const SMikkTSpaceContext* pContext, float fvTexcOut[], const int iFace, const int iVert)
+            {
+                MikktData* data = (MikktData*)pContext->m_pUserData;
+                LLVolumeFace* face = data->face;
+                S32 idx = face->mIndices[iFace * 3 + iVert];
+                auto& tc = face->mTexCoords[idx];
+                fvTexcOut[0] = tc.mV[0];
+                fvTexcOut[1] = tc.mV[1];
+            };
+
+            ms.m_setTSpaceBasic = [](const SMikkTSpaceContext* pContext, const float fvTangent[], const float fSign, const int iFace, const int iVert)
+            {
+                MikktData* data = (MikktData*)pContext->m_pUserData;
+                LLVolumeFace* face = data->face;
+                S32 i = iFace * 3 + iVert;
+                S32 idx = face->mIndices[i];
+                
+                LLVector3 p(face->mPositions[idx].getF32ptr());
+                LLVector3 n(face->mNormals[idx].getF32ptr());
+                LLVector3 t(fvTangent);
+
+                MikktKey key = { p, n };
+
+                MikktTangent& mt = data->tangents[key];
+                mt.t += t;
+                mt.s.push_back(fSign);
+                mt.i.push_back(i);
+            };
+
+            ms.m_setTSpace = nullptr;
+
+            MikktData data;
+            data.face = this;
+
+            SMikkTSpaceContext ctx = { &ms, &data };
+
+            genTangSpaceDefault(&ctx);
+
+            for (U32 i = 0; i < mNumVertices; ++i)
+            {
+                MikktKey key = { LLVector3(mPositions[i].getF32ptr()), LLVector3(mNormals[i].getF32ptr()) };
+                MikktTangent& t = data.tangents[key];
+
+                //set tangent
+                mMikktSpaceTangents[i].load3(t.t.mV);
+                mMikktSpaceTangents[i].normalize3fast();
+
+                //set sign
+                F32 sign = 0.f;
+                for (int j = 0; j < t.i.size(); ++j)
+                {
+                    if (mIndices[t.i[j]] == i)
+                    {
+                        sign = t.s[j];
+                        break;
+                    }
+                }
+
+                llassert(sign != 0.f);
+                mMikktSpaceTangents[i].getF32ptr()[3] = sign;
+            }
+        }
+        else
+        {
+            //generate tangents
+            LLVector4a* ptr = (LLVector4a*)tangents;
+
+            LLVector4a* end = mTangents + mNumVertices;
+            while (ptr < end)
+            {
+                (*ptr++).clear();
+            }
+
+            CalculateTangentArray(mNumVertices, mPositions, mNormals, mTexCoords, mNumIndices / 3, mIndices, tangents);
+        }
+
+        //normalize normals
+        for (U32 i = 0; i < mNumVertices; i++)
+        {
+            //bump map/planar projection code requires normals to be normalized
+            mNormals[i].normalize3fast();
+        }
+    }
 }
 
 void LLVolumeFace::resizeVertices(S32 num_verts)
@@ -6511,10 +6718,11 @@ void LLVolumeFace::pushVertex(const LLVector4a& pos, const LLVector4a& norm, con
 	mNumVertices++;	
 }
 
-void LLVolumeFace::allocateTangents(S32 num_verts)
+void LLVolumeFace::allocateTangents(S32 num_verts, bool mikktspace)
 {
-	ll_aligned_free_16(mTangents);
-	mTangents = (LLVector4a*) ll_aligned_malloc_16(sizeof(LLVector4a)*num_verts);
+    auto& buff = mikktspace ? mMikktSpaceTangents : mTangents;
+	ll_aligned_free_16(buff);
+	buff = (LLVector4a*) ll_aligned_malloc_16(sizeof(LLVector4a)*num_verts);
 }
 
 void LLVolumeFace::allocateWeights(S32 num_verts)
diff --git a/indra/llmath/llvolume.h b/indra/llmath/llvolume.h
index 9697952f5b..8c604c5d1a 100644
--- a/indra/llmath/llvolume.h
+++ b/indra/llmath/llvolume.h
@@ -870,10 +870,10 @@ private:
 public:
 
 	BOOL create(LLVolume* volume, BOOL partial_build = FALSE);
-	void createTangents();
+	void createTangents(bool mikktspace = false);
 	
 	void resizeVertices(S32 num_verts);
-	void allocateTangents(S32 num_verts);
+	void allocateTangents(S32 num_verts, bool mikktspace = false);
 	void allocateWeights(S32 num_verts);
     void allocateJointIndices(S32 num_verts);
 	void resizeIndices(S32 num_indices);
@@ -947,6 +947,7 @@ public:
 	LLVector4a* mPositions; // Contains vertices, nortmals and texcoords
 	LLVector4a* mNormals; // pointer into mPositions
 	LLVector4a* mTangents;
+    LLVector4a* mMikktSpaceTangents = nullptr; // for GLTF rendering, use mikkt space tangents
 	LLVector2*  mTexCoords; // pointer into mPositions
 
 	// mIndices contains mNumIndices amount of elements.
@@ -1028,7 +1029,7 @@ public:
 	void setDirty() { mPathp->setDirty(); mProfilep->setDirty(); }
 
 	void regen();
-	void genTangents(S32 face);
+    void genTangents(S32 face, bool mikktspace = false);
 
 	BOOL isConvex() const;
 	BOOL isCap(S32 face);
diff --git a/indra/newview/app_settings/settings.xml b/indra/newview/app_settings/settings.xml
index cd33690075..9508c1dc2d 100644
--- a/indra/newview/app_settings/settings.xml
+++ b/indra/newview/app_settings/settings.xml
@@ -10558,6 +10558,17 @@
     <key>Value</key>
     <integer>0</integer>
   </map>
+  <key>RenderUseMikktSpace</key>
+  <map>
+    <key>Comment</key>
+    <string>Use Mikkt Space tangents on GLTF materials.</string>
+    <key>Persist</key>
+    <integer>1</integer>
+    <key>Type</key>
+    <string>Boolean</string>
+    <key>Value</key>
+    <integer>1</integer>
+  </map>
   <key>RenderUseTriStrips</key>
   <map>
     <key>Comment</key>
diff --git a/indra/newview/app_settings/shaders/class1/deferred/pbropaqueF.glsl b/indra/newview/app_settings/shaders/class1/deferred/pbropaqueF.glsl
index f5b5698305..69019667de 100644
--- a/indra/newview/app_settings/shaders/class1/deferred/pbropaqueF.glsl
+++ b/indra/newview/app_settings/shaders/class1/deferred/pbropaqueF.glsl
@@ -42,6 +42,8 @@ uniform vec3 emissiveColor;
 
 #ifdef HAS_NORMAL_MAP
     uniform sampler2D bumpMap;
+    VARYING vec3 vary_tangent;
+    flat in float vary_sign;
 #endif
 
 #ifdef HAS_EMISSIVE_MAP
@@ -66,9 +68,6 @@ VARYING vec4 vertex_color;
 VARYING vec2 vary_texcoord0;
 #ifdef HAS_NORMAL_MAP
 VARYING vec3 vary_normal;
-VARYING vec3 vary_mat0;
-VARYING vec3 vary_mat1;
-VARYING vec3 vary_mat2;
 VARYING vec2 vary_texcoord1;
 #endif
 
@@ -94,21 +93,14 @@ void main()
 
     vec3 col = vertex_color.rgb * albedo.rgb;
 
-#ifdef HAS_NORMAL_MAP
-    vec4 norm = texture2D(bumpMap, vary_texcoord1.xy);
-    norm.xyz = normalize(norm.xyz * 2 - 1);
-
-    vec3 tnorm = vec3(dot(norm.xyz,vary_mat0),
-                      dot(norm.xyz,vary_mat1),
-                      dot(norm.xyz,vary_mat2));
-#else
-    vec4 norm = vec4(0,0,0,1.0);
-//    vec3 tnorm = vary_normal;
-    vec3 tnorm = vec3(0,0,1);
-#endif
+    // from mikktspace.com
+    vec4 vNt = texture2D(bumpMap, vary_texcoord1.xy)*2.0-1.0;
+    float sign = vary_sign;
+    vec3 vN = vary_normal;
+    vec3 vT = vary_tangent.xyz;
 
-    tnorm = normalize(tnorm.xyz);
-    norm.xyz = tnorm.xyz;
+    vec3 vB = sign * cross(vN, vT);
+    vec3 tnorm = normalize( vNt.x * vT + vNt.y * vB + vNt.z * vN );
 
     // RGB = Occlusion, Roughness, Metal
     // default values, see LLViewerTexture::sDefaultPBRORMImagep
@@ -155,6 +147,9 @@ void main()
 
     tnorm *= gl_FrontFacing ? 1.0 : -1.0;
 
+    //col = vec3(0,0,0);
+    //emissive = vary_tangent.xyz*0.5+0.5;
+    //emissive = vec3(vary_sign*0.5+0.5);
     // See: C++: addDeferredAttachments(), GLSL: softenLightF
     frag_data[0] = vec4(col, 0.0);                                                   // Diffuse
     frag_data[1] = vec4(emissive, vertex_color.a);                                   // PBR sRGB Emissive
diff --git a/indra/newview/app_settings/shaders/class1/deferred/pbropaqueV.glsl b/indra/newview/app_settings/shaders/class1/deferred/pbropaqueV.glsl
index a2606ed771..e17d91af38 100644
--- a/indra/newview/app_settings/shaders/class1/deferred/pbropaqueV.glsl
+++ b/indra/newview/app_settings/shaders/class1/deferred/pbropaqueV.glsl
@@ -59,13 +59,7 @@ ATTRIBUTE vec2 texcoord0;
 ATTRIBUTE vec4 tangent;
 ATTRIBUTE vec2 texcoord1;
 
-VARYING vec3 vary_mat0;
-VARYING vec3 vary_mat1;
-VARYING vec3 vary_mat2;
-
 VARYING vec2 vary_texcoord1;
-#else
-VARYING vec3 vary_normal;
 #endif
 
 #ifdef HAS_SPECULAR_MAP
@@ -75,6 +69,10 @@ VARYING vec2 vary_texcoord2;
  
 VARYING vec4 vertex_color;
 VARYING vec2 vary_texcoord0;
+VARYING vec3 vary_tangent;
+flat out float vary_sign;
+
+VARYING vec3 vary_normal;
 
 void main()
 {
@@ -113,9 +111,9 @@ void main()
 	vec3 t = normalize((mat*vec4(tangent.xyz+position.xyz,1.0)).xyz-pos.xyz);
 	vec3 b = cross(n, t)*tangent.w;
 	
-	vary_mat0 = vec3(t.x, b.x, n.x);
-	vary_mat1 = vec3(t.y, b.y, n.y);
-	vary_mat2 = vec3(t.z, b.z, n.z);
+	//vary_mat0 = vec3(t.x, b.x, n.x);
+	//vary_mat1 = vec3(t.y, b.y, n.y);
+	//vary_mat2 = vec3(t.z, b.z, n.z);
 #else //HAS_NORMAL_MAP
 vary_normal  = n;
 #endif //HAS_NORMAL_MAP
@@ -123,12 +121,16 @@ vary_normal  = n;
 	vec3 n = normalize(normal_matrix * normal);
 #ifdef HAS_NORMAL_MAP
 	vec3 t = normalize(normal_matrix * tangent.xyz);
-	vec3 b = cross(n,t)*tangent.w;
+    vary_tangent = t;
+    vary_sign = tangent.w;
+    vary_normal = n;
+
+	//vec3 b = cross(n,t)*tangent.w;
 	//vec3 t = cross(b,n) * binormal.w;
 	
-	vary_mat0 = vec3(t.x, b.x, n.x);
-	vary_mat1 = vec3(t.y, b.y, n.y);
-	vary_mat2 = vec3(t.z, b.z, n.z);
+	//vary_mat0 = vec3(t.x, b.x, n.x);
+	//vary_mat1 = vec3(t.y, b.y, n.y);
+	//vary_mat2 = vec3(t.z, b.z, n.z);
 #else //HAS_NORMAL_MAP
 	vary_normal = n;
 #endif //HAS_NORMAL_MAP
diff --git a/indra/newview/llface.cpp b/indra/newview/llface.cpp
index 52aacb607c..f35b4b6d91 100644
--- a/indra/newview/llface.cpp
+++ b/indra/newview/llface.cpp
@@ -2166,14 +2166,19 @@ BOOL LLFace::getGeometryVolume(const LLVolume& volume,
 			mVertexBuffer->getTangentStrider(tangent, mGeomIndex, mGeomCount, map_range);
 			F32* tangents = (F32*) tangent.get();
 			
-			mVObjp->getVolume()->genTangents(f);
+            LLGLTFMaterial* gltf_mat = tep->getGLTFMaterial();
+            static LLCachedControl<bool> use_mikktspace(gSavedSettings, "RenderUseMikktSpace");
+            bool mikktspace = use_mikktspace && gltf_mat != nullptr;
+
+			mVObjp->getVolume()->genTangents(f, mikktspace);
 			
 			LLVector4Logical mask;
 			mask.clear();
 			mask.setElement<3>();
 
-			LLVector4a* src = vf.mTangents;
-			LLVector4a* end = vf.mTangents+num_vertices;
+            LLVector4a* tbuff = mikktspace ? vf.mMikktSpaceTangents : vf.mTangents;
+			LLVector4a* src = tbuff;
+			LLVector4a* end = tbuff+num_vertices;
 
 			while (src < end)
 			{