//获取LookAt矩阵
//相机的位置 相机的看着那个位置（决定相机方向） 相机上方位置
// see:https://zhuanlan.zhihu.com/p/66384929
// Rx Ry Rz 0
// Ux Uy Uz 0
// Dx Dy Dz 0
// 0 0 0 1 相机空间是左手系
public static HMatrix GetLookAtMat(HVector camera, HVector at, HVector up)
{
HMatrix matRet = new HMatrix();
HVector CameraXAxis, CameraYAxis, CameraZAxis;
CameraZAxis = at.Sub(camera);
CameraZAxis = CameraZAxis.Normalize();
CameraYAxis = up.Normalize();
CameraXAxis = CameraZAxis.CrossProduct(CameraYAxis);
CameraXAxis = CameraXAxis.Normalize();
matRet.m[0, 0] = CameraXAxis.x;
matRet.m[1, 0] = CameraXAxis.y;
matRet.m[2, 0] = CameraXAxis.z;
matRet.m[3, 0] = -CameraXAxis.DotProduct(camera);
matRet.m[0, 1] = CameraYAxis.x;
matRet.m[1, 1] = CameraYAxis.y;
matRet.m[2, 1] = CameraYAxis.z;
matRet.m[3, 1] = -CameraYAxis.DotProduct(camera);
matRet.m[0, 2] = CameraZAxis.x;
matRet.m[1, 2] = CameraZAxis.y;
matRet.m[2, 2] = CameraZAxis.z;
matRet.m[3, 2] = -CameraZAxis.DotProduct(camera);
matRet.m[0, 3] = matRet.m[1, 3] = matRet.m[2, 3] = 0.0f;
matRet.m[3, 3] = 1.0f;
return(matRet);
}
