Function 17 - get the identifier of the pressed button.
Takes away the code of the pressed button from the buffer.
Parameters:
- eax = 17 - function number
Returned value:
- if the buffer is empty, function returns eax=1
- if the buffer is not empty, function returns al=0,
high 24 bits of eax contain button identifier (in particular, ah
contains low byte of the identifier; if all buttons have
the identifier less than 256, ah is enough to distinguish).
Remarks:
- "Buffer" keeps only one button, at pressing the new button the
information about old is lost.
- The call of this function by an application with inactive window
will return answer "buffer is empty".