GameMaker - Tile Raycast

#macro TILE_SIZE 16
#macro TILE_SIZE_M1 15
#macro TILE_RANGE 50
#macro NO_COLLISION -4

// _map is the tilemap id

function tile_raycast(_x, _y, _rx, _ry, _map)
{
    // Casts a ray to test for tile collision and returns true or false if found

    _rx -= _x;
    _ry -= _y;

    var _dot0 = _rx * _rx + _ry * _ry,
        _dist = sqrt(_dot0) + 0.00001; // safe normalize

    _rx /= _dist;
    _ry /= _dist;

    var _x_length = _ry/_rx,
        _y_length = _rx/_ry,
        _x_dist = sqrt(1 + _x_length * _x_length),
        _y_dist = sqrt(1 + _y_length * _y_length),
        _x_map  = _x div TILE_SIZE,
        _y_map  = _y div TILE_SIZE,
        _x_step = sign(_rx),
        _y_step = sign(_ry);

    if (_rx < 0) _x_length = (_x - (_x &~ TILE_SIZE_M1)) / TILE_SIZE * _x_dist;
    else  _x_length = ((_x &~ TILE_SIZE_M1) + TILE_SIZE - _x) / TILE_SIZE *_x_dist;

    if (_ry < 0) _y_length = (_y - (_y &~ TILE_SIZE_M1)) / TILE_SIZE * _y_dist;
    else _y_length = ((_y &~ TILE_SIZE_M1) + TILE_SIZE - _y) / TILE_SIZE *_y_dist;

    for (var _d = 0; _d < TILE_RANGE; _d++)
    {
        if (_x_length < _y_length)
        {
            _x_map += _x_step;
            if (tilemap_get(_map, _x_map, _y_map) & tile_index_mask == TILE_SOLID)
            {
                _dist = _x_length * TILE_SIZE;
                _rx *= _dist;
                _ry *= _dist;
                if ((_rx * _rx + _ry * _ry) > _dot0) return false;
                else return true;
            }
            _x_length += _x_dist;
        }
        else
        {
            _y_map += _y_step;
            if (tilemap_get(_map, _x_map, _y_map) & tile_index_mask == TILE_SOLID)
            {
                _dist = _y_length * TILE_SIZE;
                _rx *= _dist;
                _ry *= _dist;
                if ((_rx * _rx + _ry * _ry) > _dot0) return false;
                else return true;
            }
            _y_length += _y_dist;
        }
    }
    return false;
}

function tile_raycast_point(_x, _y, _rx, _ry, _map)
{
    // Casts a ray to (_rx, _ry) and tests for tile collision
    // Returns a point (x, y) if found or NO_COLLISION

    _rx -= _x;
    _ry -= _y;

    var _dot0 = _rx * _rx + _ry * _ry,
        _dist = sqrt(_dot0) + 0.00001; // safe normalize

    _rx /= _dist;
    _ry /= _dist;

    var _x_length = _ry/_rx,
        _y_length = _rx/_ry,
        _x_dist = sqrt(1 + _x_length * _x_length),
        _y_dist = sqrt(1 + _y_length * _y_length),
        _x_map  = _x div TILE_SIZE,
        _y_map  = _y div TILE_SIZE,
        _x_step = sign(_rx),
        _y_step = sign(_ry);

    if (_rx < 0) _x_length = (_x - (_x &~ TILE_SIZE_M1)) / TILE_SIZE * _x_dist;
    else  _x_length = ((_x &~ TILE_SIZE_M1) + TILE_SIZE - _x) / TILE_SIZE *_x_dist;

    if (_ry < 0) _y_length = (_y - (_y &~ TILE_SIZE_M1)) / TILE_SIZE * _y_dist;
    else _y_length = ((_y &~ TILE_SIZE_M1) + TILE_SIZE - _y) / TILE_SIZE *_y_dist;

    for (var _d = 0; _d < TILE_RANGE; _d++)
    {
        if (_x_length < _y_length)
        {
            _x_map += _x_step;
            if (tilemap_get(_map, _x_map, _y_map) & tile_index_mask == TILE_SOLID)
            {
                _dist = _x_length * TILE_SIZE;
                _rx *= _dist;
                _ry *= _dist;
                if ((_rx * _rx + _ry * _ry) > _dot0) return NO_COLLISION;
                else return { x : _x + _rx, y : _y + _ry }
            }
            _x_length += _x_dist;
        }
        else
        {
            _y_map += _y_step;
            if (tilemap_get(_map, _x_map, _y_map) & tile_index_mask == TILE_SOLID)
            {
                _dist = _y_length * TILE_SIZE;
                _rx *= _dist;
                _ry *= _dist;
                if ((_rx * _rx + _ry * _ry) > _dot0) return NO_COLLISION;
                else return { x : _x + _rx, y : _y + _ry }
            }
            _y_length += _y_dist;
        }
    }
    return NO_COLLISION;
}