grab, drag, and release handler framework for IUPLua

drag.lua

do
  local dox, doy
  local function drag(x, y)
  end
  local function grab(x, y)
    dox, doy = x, y
    drag(x, y)
  end
  local function release(x, y)
    dox, doy = nil, nil
  end
  
  function cnv:button_cb(but, pressed, x, y, status)
    if but == iup.BUTTON1 then
      if pressed == 1 then
        grab(x, y)
      elseif dox then
        release(x, y)
      end
    end
  end
  function cnv:motion_cb(x, y, status)
    if dox then
      if iup.isbutton1(status) then
        drag(x, y)
      else --mouse has been released without triggering button_cb
        release(x, y)
      end
    end
  end
end