void MeshUtils::calculateVertexTangents( const std::vector< Face >& faces, std::vector< LitVertex >& inOutVertices )
{
/**
* I used the algorithm from this page: http://www.terathon.com/code/tangent.html.
*/
uint vertexCount = inOutVertices.size();
Vector* tan1 = new Vector[vertexCount * 2];
Vector* tan2 = tan1 + vertexCount;
memset( tan1, 0, vertexCount * sizeof(Vector) * 2 );
Vector sdir, tdir;
uint trianglesCount = faces.size();
for ( uint i = 0; i < trianglesCount; ++i )
{
const Face& tri = faces[i];
uint i1 = tri.idx[0];
uint i2 = tri.idx[1];
uint i3 = tri.idx[2];
const TVector<3>& v1 = inOutVertices[i1].m_coords;
const TVector<3>& v2 = inOutVertices[i2].m_coords;
const TVector<3>& v3 = inOutVertices[i3].m_coords;
const TVector<2>& w1 = inOutVertices[i1].m_textureCoords;
const TVector<2>& w2 = inOutVertices[i2].m_textureCoords;
const TVector<2>& w3 = inOutVertices[i3].m_textureCoords;
float x1 = v2[0] - v1[0];
float x2 = v3[0] - v1[0];
float y1 = v2[1] - v1[1];
float y2 = v3[1] - v1[1];
float z1 = v2[2] - v1[2];
float z2 = v3[2] - v1[2];
float s1 = w2[0] - w1[0];
float s2 = w3[0] - w1[0];
float t1 = w2[1] - w1[1];
float t2 = w3[1] - w1[1];
float r = (s1 * t2 - s2 * t1);
if ( r != 0.0f )
{
r = 1.0f / r;
sdir.set( (t2 * x1 - t1 * x2) * r, (t2 * y1 - t1 * y2) * r, (t2 * z1 - t1 * z2) * r );
tdir.set( (s1 * x2 - s2 * x1) * r, (s1 * y2 - s2 * y1) * r, (s1 * z2 - s2 * z1) * r );
tan1[i1].add( sdir );
tan1[i2].add( sdir );
tan1[i3].add( sdir );
tan2[i1].add( tdir );
tan2[i2].add( tdir );
tan2[i3].add( tdir );
}
}
Vector vertexNorm, vertexTangent, normTanCross;
for ( uint i = 0; i < vertexCount; ++i )
{
vertexNorm.load( inOutVertices[i].m_normal );
const Vector& t = tan1[i];
// Gram-Schmidt orthogonalize
FastFloat normTan1Dot;
normTan1Dot.setNeg( vertexNorm.dot( t ) );
vertexTangent.setMulAdd( vertexNorm, normTan1Dot, t );
vertexTangent.normalize();
// Calculate handedness
normTanCross.setCross( vertexNorm, t );
FastFloat handedness;
handedness.setSign( normTanCross.dot( tan2[i] ) );
handedness.reciprocal();
vertexTangent.mul( handedness );
// store the results
vertexTangent.store( inOutVertices[i].m_tangent );
}
delete[] tan1;
}
