CX event mask (events which you want sent to your handler)
bit 0 = mouse movement (CX | 01H)
bit 1 = left button pressed (CX | 02H)
bit 2 = left button released (CX | 04H)
bit 3 = right button pressed (CX | 08H)
bit 4 = right button released (CX | 10H)
bit 5 = Shift down when button pressed (CX | 20H)
bit 6 = Ctrl down when button pressed (CX | 40H)
bit 7 = Alt down when button pressed (CX | 80H)
CX = 00ffH = handle all events
CX = 0000H = disable handler
ES:DX address of your event handler code
Returns: AX installation status: 0018H = installed
ffffH = Error: can't install
Info: This function is the more elegant version of INT 33H 000cH (which
see for specs on the custom handler code).
This function will inform your handler when a Shift-, Ctrl-, or
Alt- key was down when a mouse button was pressed. It also
allows you to install up to three separate event handlers,
provided that each has a different event mask in CX.
Bits 5, 6, and 7 specify the shift keys of interest. If you
If an event handler for the specified event mask (in CX) already
exists, an error is returned (AX=ffffH upon return). In that
previous handler. You may de-install that handler, install your
own, then re-install the old one later.
To de-install an alternate event handler, call this function with
the address of the handler and 0's in relevant bits of the event
mask. You should de-install event handlers before exiting your