Subversion Repositories gelsvn

	void Quaternion::make_rot(const Mat4x4f& m)

	{

		float trace = m[0][0] + m[1][1] + m[2][2]  + 1.0f;

		//If the trace of the matrix is greater than zero, then

		//perform an "instant" calculation.

		if ( trace > TINY ) 

		{

			float S = sqrt(trace) * 2.0f;

			qv = Vec3f(m[2][1] - m[1][2], m[0][2] - m[2][0], m[1][0] - m[0][1] );

			qv /= S;

			qw = 0.25f * S;

		}

		else

		{

			//If the trace of the matrix is equal to zero (or negative...) then identify

			//which major diagonal element has the greatest value.

			//Depending on this, calculate the following:

			if ( m[0][0] > m[1][1] && m[0][0] > m[2][2] )  {	// Column 0: 

				float S  = sqrt( 1.0 + m[0][0] - m[1][1] - m[2][2] ) * 2.0f;

				qv[0] = 0.25f * S;

				qv[1] = (m[1][0] + m[0][1] ) / S;

				qv[2] = (m[0][2] + m[2][0] ) / S;

				qw = (m[2][1] - m[1][3] ) / S;

			} else if ( m[1][1] > m[2][2] ) {			// Column 1: 

				float S  = sqrt( 1.0 + m[1][1] - m[0][0] - m[2][2] ) * 2.0f;

				qv[0] = (m[1][0] + m[0][1] ) / S;

				qv[1] = 0.25f * S;

				qv[2] = (m[2][1] + m[1][2] ) / S;

				qw = (m[0][2] - m[2][0] ) / S;

			} else {						// Column 2:

				float S  = sqrt( 1.0 + m[2][2] - m[0][0] - m[1][1] ) * 2.0f;

				qv[0] = (m[0][2] + m[2][0] ) / S;

				qv[1] = (m[2][1] + m[1][2] ) / S;

				qv[2] = 0.25f * S;

				qw = (m[1][0] - m[0][1] ) / S;

			}

		}

		//The quaternion is then defined as:

		//  Q = | X Y Z W |

	}