wheelDelta = GetMouseWheel([mouseIndex])
Return change of mouse wheel position of a wheel mouse (in “wheel clicks”)
since last query. ‘mouseIndex’ is the device index of the wheel mouse to
query. The argument is optional: If left out, the first detected real wheel
mouse is queried.
OS X: _____________________________________________________________________
Uses PsychHID for low-level access to mice with mouse wheels. If wheel
state is not queried frequent enough, the internal queue may overflow and
some mouse wheel movements may get lost, resulting in a smaller reported
‘wheelDelta’ than the real delta since last query. On OS X 10.4.11 the
operating system can store at most 10 discrete wheel movements before it
discards movement events. This uses low-level code which may not work on
all wheel mice.
Uses GetMouse() extra valuators to check if one of the valuators represents
a mouse wheel, then translates the valuators absolute wheel position into
wheel delta by keeping track of old values.
This function is not supported and will fail with an error.