three.js/src/core/Matrix3.js

/**
 * @author alteredq / http://alteredqualia.com/
 */

THREE.Matrix3 = function () {

	this.elements = new Float32Array(9);

};

THREE.Matrix3.prototype = {

	constructor: THREE.Matrix3,

	getInverse: function ( matrix ) {

		// input: THREE.Matrix4
		// ( based on http://code.google.com/p/webgl-mjs/ )

        var me = matrix.elements;
        
		var a11 =   me[10] * me[5] - me[6] * me[9];
		var a21 = - me[10] * me[1] + me[2] * me[9];
		var a31 =   me[6] * me[1] - me[2] * me[5];
		var a12 = - me[10] * me[4] + me[6] * me[8];
		var a22 =   me[10] * me[0] - me[2] * me[8];
		var a32 = - me[6] * me[0] + me[2] * me[4];
		var a13 =   me[9] * me[4] - me[5] * me[8];
		var a23 = - me[9] * me[0] + me[1] * me[8];
		var a33 =   me[5] * me[0] - me[1] * me[4];

		var det = me[0] * a11 + me[1] * a12 + me[2] * a13;

		// no inverse

		if ( det === 0 ) {

			console.warn( "Matrix3.getInverse(): determinant == 0" );

		}

		var idet = 1.0 / det;

		var m = this.elements;

		m[ 0 ] = idet * a11; m[ 1 ] = idet * a21; m[ 2 ] = idet * a31;
		m[ 3 ] = idet * a12; m[ 4 ] = idet * a22; m[ 5 ] = idet * a32;
		m[ 6 ] = idet * a13; m[ 7 ] = idet * a23; m[ 8 ] = idet * a33;

		return this;

	},

	
	transpose: function () {

		var tmp, m = this.elements;

		tmp = m[1]; m[1] = m[3]; m[3] = tmp;
		tmp = m[2]; m[2] = m[6]; m[6] = tmp;
		tmp = m[5]; m[5] = m[7]; m[7] = tmp;

		return this;

	},
	

	transposeIntoArray: function ( r ) {

		var m = this.m;

		r[ 0 ] = m[ 0 ];
		r[ 1 ] = m[ 3 ];
		r[ 2 ] = m[ 6 ];
		r[ 3 ] = m[ 1 ];
		r[ 4 ] = m[ 4 ];
		r[ 5 ] = m[ 7 ];
		r[ 6 ] = m[ 2 ];
		r[ 7 ] = m[ 5 ];
		r[ 8 ] = m[ 8 ];

		return this;

	}

};