How do I saving the results of a pixelated render to an image file?

Question

I rendered a large coordinate text file (16M lines) into a pixelated picture. How do I go about saving the results to an image file? I created it on a black background TextureRec using the code below:

func _draw():
    var f = File.new()
    f.open(file, File.READ)
    #for loop in range(0,1000000):
    while not f.eof_reached():
        var line = f.get_line()
        if (line == null):
            f.close()
            print('done')
            return

        var xcoord = (int(line.get_slice(",", 0))/40)
        var ycoord = (int(line.get_slice(",", 1))/40)

        var point = PoolVector2Array([Vector2(xcoord, ycoord)])
        var color = PoolColorArray([Color(255, 0, 0)])
        draw_primitive(point, color, PoolVector2Array())

    f.close()
    print('done')
    return