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rollercoastergeometry 안에

var sides = 5;
	var step1 = [ ];
	for ( var i = 0; i < sides; i ++ ) {

		var angle = ( i / sides ) * PI2;	//angle이 72, 144, 216, 288, 360 다섯 가지가 됨
		step1.push( new THREE.Vector3(0 , Math.sin( angle ) * 0.02, Math.cos( angle ) * 0.02 ) );

	}
..................

function extrudeShapeSide( shape, fromPoint, toPoint, color ) {

		for ( var j = 0, jl = shape.length; j < jl; j ++ ) {

			var point1 = shape[ j ];
			var point2 = shape[ ( j + 1 ) % jl ];

			vector1.copy( point1 );
			vector1.applyQuaternion( quaternion );
			vector1.add( fromPoint );

			vector2.copy( point2 );
			vector2.applyQuaternion( quaternion );
			vector2.add( fromPoint );

			vector3.copy( point2 );
			vector3.applyQuaternion( quaternion );
			vector3.add( toPoint );

			vector4.copy( point1 );
			vector4.applyQuaternion( quaternion );
			vector4.add( toPoint );

			vertices.push( vector1.x, vector1.y, vector1.z );
			vertices.push( vector2.x, vector2.y, vector2.z );
			vertices.push( vector4.x, vector4.y, vector4.z );

			vertices.push( vector2.x, vector2.y, vector2.z );
			vertices.push( vector3.x, vector3.y, vector3.z );
			vertices.push( vector4.x, vector4.y, vector4.z );

			//

			normal1.copy( point1 );
			normal1.applyQuaternion( quaternion );
			normal1.normalize();

			normal2.copy( point2 );
			normal2.applyQuaternion( quaternion );
			normal2.normalize();

			normal3.copy( point2 );
			normal3.applyQuaternion( quaternion );
			normal3.normalize();

			normal4.copy( point1 );
			normal4.applyQuaternion( quaternion );
			normal4.normalize();

			normals.push( normal1.x, normal1.y, normal1.z );
			normals.push( normal2.x, normal2.y, normal2.z );
			normals.push( normal4.x, normal4.y, normal4.z );

			normals.push( normal2.x, normal2.y, normal2.z );
			normals.push( normal3.x, normal3.y, normal3.z );
			normals.push( normal4.x, normal4.y, normal4.z );

			colors.push( color[ 0 ], color[ 1 ], color[ 2 ] );
			colors.push( color[ 0 ], color[ 1 ], color[ 2 ] );
			colors.push( color[ 0 ], color[ 1 ], color[ 2 ] );

			colors.push( color[ 0 ], color[ 1 ], color[ 2 ] );
			colors.push( color[ 0 ], color[ 1 ], color[ 2 ] );
			colors.push( color[ 0 ], color[ 1 ], color[ 2 ] );

		}

	};

var fromPoint = new THREE.Vector3();
var toPoint = new THREE.Vector3();
........

		if ( i % 2 === 0 ) {
			//가운데 노란 레일 양 옆에 노란색 세모 두 개 그리기
			fromPoint.set(-0.2,-0.02,0);
			fromPoint.applyQuaternion( quaternion );
			fromPoint.add( point );

			toPoint.set(0,-0.135,0);
			toPoint.applyQuaternion( quaternion );
			toPoint.add( point );
			extrudeShapeSide(step1, fromPoint, toPoint, color2);

			fromPoint.set(0.2,-0.02,0);
			fromPoint.applyQuaternion( quaternion );
			fromPoint.add( point );

			toPoint.set(0,-0.135,0);
			toPoint.applyQuaternion( quaternion );
			toPoint.add( point );
			extrudeShapeSide(step1, fromPoint, toPoint, color2);
		}