gwQuaternion.cpp

/*************************************************************************\
 Engine: gearWorks
 File: gwQuaternion.cpp
 Author: Zachry Thayer
 Description: implements quaternions
 Requires: 
\*************************************************************************/

#include "gwQuaternion.h"

gwQuaternion::gwQuaternion()
{
	m_x = m_y = m_z = 0.0f;
	m_w = 1.0f;
}

gwQuaternion::~gwQuaternion()
{

}

void gwQuaternion::createFromAxisAngle(float x, float y, float z, float degrees)
{
	// First we want to convert the degrees to radians 
	// since the angle is assumed to be in radians
	float angle = float((degrees / 180.0f) * PI);

	// Here we calculate the sin( theta / 2) once for optimization
	float result = (float)sin( angle / 2.0f );
		
	// Calcualte the w value by cos( theta / 2 )
	m_w = (float)cos( angle / 2.0f );

	// Calculate the x, y and z of the quaternion
	m_x = float(x * result);
	m_y = float(y * result);
	m_z = float(z * result);
}

void gwQuaternion::createMatrix(float *pMatrix)
{
	// Make sure the matrix has allocated memory to store the rotation data
	if(!pMatrix) return;

	// First row
	pMatrix[ 0] = 1.0f - 2.0f * ( m_y * m_y + m_z * m_z ); 
	pMatrix[ 1] = 2.0f * (m_x * m_y + m_z * m_w);
	pMatrix[ 2] = 2.0f * (m_x * m_z - m_y * m_w);
	pMatrix[ 3] = 0.0f;  

	// Second row
	pMatrix[ 4] = 2.0f * ( m_x * m_y - m_z * m_w );  
	pMatrix[ 5] = 1.0f - 2.0f * ( m_x * m_x + m_z * m_z ); 
	pMatrix[ 6] = 2.0f * (m_z * m_y + m_x * m_w );  
	pMatrix[ 7] = 0.0f;  

	// Third row
	pMatrix[ 8] = 2.0f * ( m_x * m_z + m_y * m_w );
	pMatrix[ 9] = 2.0f * ( m_y * m_z - m_x * m_w );
	pMatrix[10] = 1.0f - 2.0f * ( m_x * m_x + m_y * m_y );  
	pMatrix[11] = 0.0f;  

	// Fourth row
	pMatrix[12] = 0;  
	pMatrix[13] = 0;  
	pMatrix[14] = 0;  
	pMatrix[15] = 1.0f;

	// Now pMatrix[] is a 4x4 homogeneous matrix that can be applied to an OpenGL Matrix
}

gwQuaternion gwQuaternion::operator *(gwQuaternion q)
{
	gwQuaternion r;

	r.m_w = m_w*q.m_w - m_x*q.m_x - m_y*q.m_y - m_z*q.m_z;
	r.m_x = m_w*q.m_x + m_x*q.m_w + m_y*q.m_z - m_z*q.m_y;
	r.m_y = m_w*q.m_y + m_y*q.m_w + m_z*q.m_x - m_x*q.m_z;
	r.m_z = m_w*q.m_z + m_z*q.m_w + m_x*q.m_y - m_y*q.m_x;
	
	return(r);
}