[[
vector3(x, y, z)

-> {
    clear = <function 8>,
    clone = <function 9>,
    cross = <function 10>,
    dist_to = <function 11>,
    dist_to_2d = <function 12>,
    dot = <function 13>,
    draw_line = <function 14>,
    draw_text = <function 15>,
    is_zero = <function 16>,
    length = <function 17>,
    length_2d = <function 18>,
    length_2d_sqr = <function 19>,
    length_sqr = <function 20>,
    lerp = <function 21>,
    normalize = <function 22>,
    normalize_no_len = <function 23>,
    normalized = <function 24>,
    to_screen = <function 25>,
    trace_bullet = <function 26>,
    trace_line = <function 27>,
    unpack = <function 28>
  }
}
]]

local function get_closest_point(a, b, c)
    local len = a:dist_to(b)
    local dist_min = INF
    local closest = nil

    for i=1, len do
        local fraction = i/len
        local pos = a:lerp(b, fraction)
        local dist = pos:dist_to(c)
        if dist_min > dist then
            dist_min = dist
            closest = pos
        end
    end

    return closest
end

-- in get_shot_yaw(start_pos, end_pos)

local closest = get_closest_point(start_pos, end_pos, head_pos)
local closest_dist = closest:dist_to(head_pos)