three.js/src/core/Quaternion.js

/*
 * @author mikael emtinger / http://gomo.se/
 * @author alteredq / http://alteredqualia.com/
 */

THREE.Quaternion = function( x, y, z, w ) {

	this.set(

		x || 0,
		y || 0,
		z || 0,
		w !== undefined ? w : 1

	);

};

THREE.Quaternion.prototype = {

	set : function ( x, y, z, w ) {

		this.x = x;
		this.y = y;
		this.z = z;
		this.w = w;

		return this;

	},

	copy : function ( q ) {

		this.x = q.x;
		this.y = q.y;
		this.z = q.z;
		this.w = q.w;

		return this;

	},

	setFromEuler : function ( vec3 ) {

		var c = 0.5 * Math.PI / 360, // 0.5 is an optimization
		x = vec3.x * c,
		y = vec3.y * c,
		z = vec3.z * c,

		c1 = Math.cos( y  ),
		s1 = Math.sin( y  ),
		c2 = Math.cos( -z ),
		s2 = Math.sin( -z ),
		c3 = Math.cos( x  ),
		s3 = Math.sin( x  ),

		c1c2 = c1 * c2,
		s1s2 = s1 * s2;

		this.w = c1c2 * c3  - s1s2 * s3;
	  	this.x = c1c2 * s3  + s1s2 * c3;
		this.y = s1 * c2 * c3 + c1 * s2 * s3;
		this.z = c1 * s2 * c3 - s1 * c2 * s3;

		return this;

	},

	setFromAxisAngle: function ( axis, angle ) {

		// from http://www.euclideanspace.com/maths/geometry/rotations/conversions/angleToQuaternion/index.htm
		// axis have to be normalized

		var halfAngle = angle / 2,
			s = Math.sin( halfAngle );

		this.x = axis.x * s;
		this.y = axis.y * s;
		this.z = axis.z * s;
		this.w = Math.cos( halfAngle );

		return this;

	},
	
	calculateW  : function () {

		this.w = - Math.sqrt( Math.abs( 1.0 - this.x * this.x - this.y * this.y - this.z * this.z ) );

		return this;

	},

	inverse : function () {

		this.x *= -1;
		this.y *= -1;
		this.z *= -1;

		return this;

	},

	length : function () {

		return Math.sqrt( this.x * this.x + this.y * this.y + this.z * this.z + this.w * this.w );

	},

	normalize : function () {

		var l = Math.sqrt( this.x * this.x + this.y * this.y + this.z * this.z + this.w * this.w );

		if ( l == 0 ) {

			this.x = 0;
			this.y = 0;
			this.z = 0;
			this.w = 0;

		} else {

			l = 1 / l;

			this.x = this.x * l;
			this.y = this.y * l;
			this.z = this.z * l;
			this.w = this.w * l;

		}

		return this;

	},

	multiplySelf : function ( quat2 ) {

		var qax = this.x,  qay = this.y,  qaz = this.z,  qaw = this.w,
		qbx = quat2.x, qby = quat2.y, qbz = quat2.z, qbw = quat2.w;

		this.x = qax * qbw + qaw * qbx + qay * qbz - qaz * qby;
		this.y = qay * qbw + qaw * qby + qaz * qbx - qax * qbz;
		this.z = qaz * qbw + qaw * qbz + qax * qby - qay * qbx;
		this.w = qaw * qbw - qax * qbx - qay * qby - qaz * qbz;

		return this;

	},

	multiply: function ( q1, q2 ) {

		// from http://www.euclideanspace.com/maths/algebra/realNormedAlgebra/quaternions/code/index.htm

		this.x =  q1.x * q2.w + q1.y * q2.z - q1.z * q2.y + q1.w * q2.x;
		this.y = -q1.x * q2.z + q1.y * q2.w + q1.z * q2.x + q1.w * q2.y;
		this.z =  q1.x * q2.y - q1.y * q2.x + q1.z * q2.w + q1.w * q2.z;
		this.w = -q1.x * q2.x - q1.y * q2.y - q1.z * q2.z + q1.w * q2.w;
		
		return this;

	},

	multiplyVector3 : function ( vec, dest ) {

		if( !dest ) { dest = vec; }

		var x    = vec.x,  y  = vec.y,  z  = vec.z,
			qx   = this.x, qy = this.y, qz = this.z, qw = this.w;

		// calculate quat * vec

		var ix =  qw * x + qy * z - qz * y,
			iy =  qw * y + qz * x - qx * z,
			iz =  qw * z + qx * y - qy * x,
			iw = -qx * x - qy * y - qz * z;

		// calculate result * inverse quat

		dest.x = ix * qw + iw * -qx + iy * -qz - iz * -qy;
		dest.y = iy * qw + iw * -qy + iz * -qx - ix * -qz;
		dest.z = iz * qw + iw * -qz + ix * -qy - iy * -qx;

		return dest;

	}

}

THREE.Quaternion.slerp = function ( qa, qb, qm, t ) {

	var cosHalfTheta = qa.w * qb.w + qa.x * qb.x + qa.y * qb.y + qa.z * qb.z;

	if ( Math.abs( cosHalfTheta ) >= 1.0 ) {

		qm.w = qa.w; qm.x = qa.x; qm.y = qa.y; qm.z = qa.z;
		return qm;

	}

	var halfTheta = Math.acos( cosHalfTheta ),
	sinHalfTheta = Math.sqrt( 1.0 - cosHalfTheta * cosHalfTheta );

	if ( Math.abs( sinHalfTheta ) < 0.001 ) { 

		qm.w = 0.5 * ( qa.w + qb.w );
		qm.x = 0.5 * ( qa.x + qb.x );
		qm.y = 0.5 * ( qa.y + qb.y );
		qm.z = 0.5 * ( qa.z + qb.z );

		return qm;

	}

	var ratioA = Math.sin( ( 1 - t ) * halfTheta ) / sinHalfTheta,
	ratioB = Math.sin( t * halfTheta ) / sinHalfTheta; 

	qm.w = ( qa.w * ratioA + qb.w * ratioB );
	qm.x = ( qa.x * ratioA + qb.x * ratioB );
	qm.y = ( qa.y * ratioA + qb.y * ratioB );
	qm.z = ( qa.z * ratioA + qb.z * ratioB );

	return qm;

}