Raytrace2D

/// Raytrace2D(tilemap_id, x0, x1, y0, y1)
/// @function Raytrace2D
/// @description Traces a line through grid squares, and returns a list of those squares.
/// @param {real} tilemap_id
/// @param {real} x0
/// @param {real} x1
/// @param {real} y0
/// @param {real} y1

var tile_size = 32;
var solid_ary = [];
var tilemap = argument[0];
var x0 = argument[1];
var x1 = argument[2];
var y0 = argument[3];
var y1 = argument[4];

var dx = abs(x1 - x0);
var dy = abs(y1 - y0);

var nx = floor(x0);
var ny = floor(y0);

var n = 1;
var x_inc, y_inc;
var error;

if(x1 >= x0)
{
    x_inc = 1;
    n += floor(x1) - nx;
    error = (floor(x0) + 1 - x0) * dy;
}
else
{
    x_inc = -1;
    n += nx - floor(x1);
    error = (x0 - floor(x0)) * dy;
}

if(y1 > y0)
{
    y_inc = 1;
    n += floor(y1) - ny;
    error -= (floor(y0) + 1 - y0) * dx;
}
else
{
    y_inc = -1;
    n += ny - floor(y1);
    error -= (y0 - floor(y0)) * dx;
}

for(; n > 0; n--)
{
    var tile_result = tilemap_get_at_pixel(tilemap, nx, ny);

    if(tile_result != 0 && tile_result != 4 && tile_result != 5)
    {
        var trace_result = [nx, ny, tile_result];
        return trace_result;
    }

    if(error > 0)
    {
        ny += y_inc;
        error -= dx;
    }
    else
    {
        nx += x_inc;
        error += dy;
    }
}

return undefined;