program define drline
    version 4.0

    local xl1      = `1'
    local yl1      = `2'
    local xl2      = `3'
    local yl2      = `4'

    local xl1 = int($AX * `xl1' + $BX)
    local yl1 = int($AY * `yl1' + $BY)
    local xl2 = int($AX * `xl2' + $BX)
    local yl2 = int($AY * `yl2' + $BY)

    gph line `yl1' `xl1' `yl2' `xl2' 1

end