This message is sent to the window that has captured joystick 1 when a button is pressed.
WORD wParam
Indicates which button has changed state. It can be any one of the following combined with any of the flags defined in MM_JOY1MOVE.
JOY_BUTTON1CHG
Set if first joystick button has changed.
JOY_BUTTON2CHG
Set if second joystick button has changed.
JOY_BUTTON3CHG
Set if third joystick button has changed.
JOY_BUTTON4CHG
Set if fourth joystick button has changed.
DWORD lParam
The low-order word contains the current x-position of the joystick. The high-order word contains the current y-position.
None
MM_JOY1BUTTONUP