（转）Ogre中计算Tangent, 感觉很不错！

代码

Vector3 Math::calculateTangentSpaceVector(
const Vector3& position1, const Vector3& position2, const Vector3& position3,
Real u1, Real v1, Real u2, Real v2, Real u3, Real v3)
{
//side0 is the vector along one side of the triangle of vertices passed in,
//and side1 is the vector along another side. Taking the cross product of these returns the normal.
Vector3 side0 = position1 - position2;
Vector3 side1 = position3 - position1;
//Calculate face normal
Vector3 normal = side1.crossProduct(side0);
normal.normalise();
//Now we use a formula to calculate the tangent.
Real deltaV0 = v1 - v2;
Real deltaV1 = v3 - v1;
Vector3 tangent = deltaV1 * side0 - deltaV0 * side1;
tangent.normalise();
//Calculate binormal
Real deltaU0 = u1 - u2;
Real deltaU1 = u3 - u1;
Vector3 binormal = deltaU1 * side0 - deltaU0 * side1;
binormal.normalise();
//Now, we take the cross product of the tangents to get a vector which
//should point in the same direction as our normal calculated above.
//If it points in the opposite direction (the dot product between the normals is less than zero),
//then we need to reverse the s and t tangents.
//This is because the triangle has been mirrored when going from tangent space to object space.
//reverse tangents if necessary
Vector3 tangentCross = tangent.crossProduct(binormal);
if (tangentCross.dotProduct(normal) < 0.0f)
{
tangent = -tangent;
binormal = -binormal;
}

return tangent;

}