function handleTriangle( context, a, b, c, ua, ub, uc ) {

			vA = context.vertices[ a ];
			vB = context.vertices[ b ];
			vC = context.vertices[ c ];

			uvA = uv[ ua ];
			uvB = uv[ ub ];
			uvC = uv[ uc ];

			x1 = vB.x - vA.x;
			x2 = vC.x - vA.x;
			y1 = vB.y - vA.y;
			y2 = vC.y - vA.y;
			z1 = vB.z - vA.z;
			z2 = vC.z - vA.z;

			s1 = uvB.u - uvA.u;
			s2 = uvC.u - uvA.u;
			t1 = uvB.v - uvA.v;
			t2 = uvC.v - uvA.v;

			r = 1.0 / ( s1 * t2 - s2 * t1 );
			sdir.set( ( t2 * x1 - t1 * x2 ) * r,
					  ( t2 * y1 - t1 * y2 ) * r,
					  ( t2 * z1 - t1 * z2 ) * r );
			tdir.set( ( s1 * x2 - s2 * x1 ) * r,
					  ( s1 * y2 - s2 * y1 ) * r,
					  ( s1 * z2 - s2 * z1 ) * r );

			tan1[ a ].addSelf( sdir );
			tan1[ b ].addSelf( sdir );
			tan1[ c ].addSelf( sdir );

			tan2[ a ].addSelf( tdir );
			tan2[ b ].addSelf( tdir );
			tan2[ c ].addSelf( tdir );

		}
@author mrdoob / http://mrdoob.com/
@author kile / http://kile.stravaganza.org/
@author alteredq / http://alteredqualia.com/
@author mikael emtinger / http://gomo.se/
@author zz85 / http://www.lab4games.net/zz85/blog