坐标变化

transformVertex( vertexPosition, mvPosition, center, scale, sin, cos )

function transformVertex( vertexPosition, mvPosition, center, scale, sin, cos ) {

    // compute position in camera space
    _alignedPosition.subVectors( vertexPosition, center ).addScalar( 0.5 ).multiply( scale );

    // to check if rotation is not zero
    if ( sin !== undefined ) {

        _rotatedPosition.x = ( cos * _alignedPosition.x ) - ( sin * _alignedPosition.y );
        _rotatedPosition.y = ( sin * _alignedPosition.x ) + ( cos * _alignedPosition.y );

    } else {

        _rotatedPosition.copy( _alignedPosition );

    }


    vertexPosition.copy( mvPosition );
    vertexPosition.x += _rotatedPosition.x;
    vertexPosition.y += _rotatedPosition.y;

    // transform to world space
    vertexPosition.applyMatrix4( _viewWorldMatrix );

}

############################