Adapt to user zooming into axis

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Thu, 11/05/2020 - 01:49 pm

I have a graph with some data, attached to it a free axis and an axis hook function. The axis hook function should run some code whenever a user zooms in or out of an trace/image.

Fuction Setup()
    Make/O data = p
    Make/O largedata = p + 100
End

Function AxisHook(s)
    STRUCT WMAxisHookStruct &s
   
    print "called with", s
End

Window Graph0() : Graph
    PauseUpdate; Silent 1       // building window...
    Display /W=(95.25,263,612,634.25) data
    NewFreeAxis/O/L test
    ModifyFreeAxis/Z test,master= bottom,hook= AxisHook
    ModifyGraph nticks(test)=0
    ModifyGraph axThick(test)=0
    ModifyGraph lblPos(left)=47
    ModifyGraph freePos(test)=-50
    SetAxis left -7.63192488262911,144.768075117371
EndMacro

Now this works for my use case.

But when I add more data to it via

AppendToGraph largeData

my hook function get's also called. But I would like to distinguish the case of users zooming into the axis and code changing the axis limits. Or to rephrase I actually want to run the code *only* when the user zooms in/out interactively and not when doing it programmatically.

Is that possible? Am I doing it right?

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

 

November 5, 2020 at 04:51 pm - Permalink

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

November 5, 2020 at 04:56 pm - Permalink

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.

November 5, 2020 at 05:03 pm - Permalink

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.

November 5, 2020 at 05:15 pm - Permalink

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.

November 15, 2020 at 07:43 am - Permalink