if active {

    //initialize
    var x_temp, y_temp, x_target, y_target, h_collision_list, v_collision_list, _c, i, _n, _n2;

    x_prev = x + x_slop;
    y_prev = y + y_slop;
    x_temp = x_prev;
    y_temp = y_prev;
    x_target = x_prev + x_speed;
    y_target = y_prev + y_speed;
    h_collision_list = ds_list_create();
    v_collision_list = ds_list_create();

    //get h_collision_list
    if x_speed < 0 and bool( collision_rectangle( bbox_left + x_slop + x_speed, bbox_top, bbox_left + x_slop, bbox_bottom, tmp_block, 0, 1 ) ) {

        _c = 0;
        while _c != noone {

            _c = collision_rectangle( bbox_left + x_slop + x_speed, bbox_top, bbox_left + x_slop, bbox_bottom, tmp_block, 0, 1 );
            if _c != noone {

                ds_list_add( h_collision_list, _c );
                instance_deactivate_object( _c );

            }

        }

        //truncate x_speed to nearest obstacle if needed
        if ds_list_size( h_collision_list ) > 0 {

            _n = x_target;
            for ( i = 0; i < ds_list_size( h_collision_list ); i++ ) {

                instance_activate_object( ds_list_find_value( h_collision_list, i ) );
                _n2 = ds_list_find_value( h_collision_list, i );
                if _n2 > _n _n = _n2;

            }

            x_target = _n2;

        }

    }

    if x_speed > 0 and bool( collision_rectangle( bbox_right + x_slop, bbox_top, bbox_left + x_slop + x_speed, bbox_bottom, tmp_block, 0, 1 ) ) {

        _c = 0;
        while _c != noone {

            _c = collision_rectangle( bbox_right + x_slop, bbox_top, bbox_left + x_slop + x_speed, bbox_bottom, tmp_block, 0, 1 );
            if _c != noone {

                ds_list_add( h_collision_list, _c );
                instance_deactivate_object( _c )

            }

        }

        //truncate x_speed to nearest obstacle if needed
        if ds_list_size( h_collision_list ) > 0 {

            _n = x_target;
            for ( i = 0; i < ds_list_size( h_collision_list ); i++ ) {

                instance_activate_object( ds_list_find_value( h_collision_list, i ) );
                _n2 = ds_list_find_value( h_collision_list, i );
                if _n2 < _n _n = _n2;

            }

            x_target = _n2;

        }

    }

}