Adapt to user zooming into axis

Hmm, that is surprisingly difficult. There seems to be no way to tell from the axis hook what event called the hook function. I came up with a somewhat kludgy workaround which saves the latest axis scaling in the graph's user data and only calls code if the axis range has changed (which happens when zooming):

Function AxisHook(s)
    STRUCT WMAxisHookStruct &s
    
    String putRange, lastZoom = GetUserData(s.win,"","axisRange")
    sprintf putRange, "%f;%f;", s.min, s.max
    SetWindow $(s.win), userdata(axisRange)=putRange
    
    Variable zoomCall = 0
    if (strlen(lastZoom) > 0)
        Variable left = str2num(StringFromList(0,lastZoom))
        Variable right = str2num(StringFromList(1,lastZoom))
        if ( ((left - s.min) > 1e-6) || ((right - s.max) > 1e-6))
            zoomCall = 1    
        endif
    endif
    
    if (zoomCall)
        print "called with", s
    endif
End

Unfortunately, the axis range changes when you add a trace with different range, and also when the user changes the axis range.

Oh, that's right! So my example was not very useful. That's really an uphill battle, but one could use the same method to store a list of displayed traces on the graph and compare if something has changed between calls. I don't see how one can distinguish user's zooming in from any other event which changes the axis range.

You may need to have a button to turn the zoom feature (your hook function) on/off.

You may need to lock out any ability to manually add data to the graph and instead force the user to run a function instead (e.g. myappendtograph).

Doesn't Igor give an option to know what the last issued command was? Can that be tested in the hook function to distinguish a command-line input appendtograph and thereby ignore break from the hook?

Of these three, I might find the first the easiest to do even as it adds the overhead for the UI on the user.

Thanks all for your input. I've now found a solution. I've ditched the axis hook approach and went with a normal window hook. The code is basically

Function PA_TraceWindowHook(s)
    STRUCT WMWinHookStruct &s
 
    string traceGraph
 
    switch(s.eventcode)
        case 22: // mouse wheel
        case 6: // resize
            traceGraph = s.winName
            Execute/P/Q "PA_UpdateScaleBars(\"" + traceGraph + "\", 0)"
            break
        case 10: // menu
            if(!cmpstr(s.menuName, "Graph") && !cmpstr(s.menuItem, "Autoscale Axes"))
                traceGraph = s.winName
                Execute/P/Q "PA_UpdateScaleBars(\"" + traceGraph + "\", 1)"
            endif
            break
    endswitch
 
    return 0
End

where PA_UpdateScaleBars reacts to the user zooming into an axis via the mouse wheel, and the menu reset the scale bars on Ctrl+a. I had to use the operation queue here so that it is executed after the axis has been rescaled by IP.