Bouncing Cat Window (Autohotkey)

CoordMode "Mouse", "Screen"
CoordMode "ToolTip", "Screen"
#R::Reload
SetWinDelay 0

MyGui := Gui(, "")
MyGui.Opt("ToolWindow -Sysmenu +AlwaysOnTop")
MyGui.SetFont "s36 w700"
MyGui.BackColor := "dddddd"
MyGui.Add("Text", "x4 y-24", ".!.")
MyGui.SetFont "s16 w400"
MyGui.Add("Text", "w12 xp+16 yp+41", "^")
WinSetStyle("0x800000", MyGui)
MyGui.Show("w50 h40 Center NoActivate")

OnMessage(0x201, WM_MouseDown)
; OnMessage(0x202, WM_MouseUp)
lastX := 0
lastY := 0
dx := 0
dy := 0
falling := false
grabbed := false
enableMove := true

WM_MouseDown(wParam, lParam, msg, window) {
  global grabbed

  if (window != MyGui.Hwnd) {
    return
  }

  grabbed := true
  MouseGetPos &mouseX, &mouseY
  lastX := mouseX
  lastY := mouseY
}

~LButton Up::MouseUp
MouseUp() {
  global grabbed
  if grabbed {
    grabbed := false
    fall
  }
}

acc := 1.0
vel := 0.0
pos := 0.0
fall() {
    global vel
    global acc
    global pos
  global falling
  offset := 82

  falling := true

    WinGetPos ,&startPos,,, MyGui
    pos := startPos

    while (abs(vel) > 0.5 or (A_ScreenHeight - abs(pos+offset) > 2)) {
    if grabbed {
      break
    }
        Sleep 1
        vel += acc
        pos += vel

        WinGetPos &xpos,,,, MyGui
        if (pos+offset > A_ScreenHeight) {
            WinMove xpos, A_ScreenHeight-offset,,, MyGui
            vel := -0.8*abs(vel)
        } else
        WinMove xpos, pos,,, MyGui
    }
    WinGetPos &endpos,,,, MyGui
  if (!grabbed) {
    WinMove endPos, A_ScreenHeight-offset,,, MyGui
  }
    vel := 0
    pos := 0
  SetTimer () => falling := false, -50
}

sleep 100
fall()

while true {
  global dx
  global dy
  global lastX
  global lastY
  global grabbed


  WinGetPos &winx, &winy,,, MyGui
  MouseGetPos &x, &y
  dx := x-lastX
  dy := y-lastY
  lastX := x
  lastY := y

  if (!falling && grabbed && enableMove) {
    WinMove winx+dx, winy+dy,,, MyGui
  }

  sleep 0
}