out of stack space when using slider

#pragma rtGlobals=3     // Use modern global access method and strict wave access.

//EXECUTE THIS TO SHOW THE DEMO
Function start()
    //---generate dummy data
    Make/O/N=(100,100,500) images
    Setscale/I z, 0, 65535, images
    images[][][] = z
   
    //---extract the first frame
    ImageTransform/P=0 getplane images
    Wave m_imageplane
    Duplicate/O m_imageplane, currentframe
   
    //---display
    showimage()
End


Function showimage()
    Wave images

    DoWindow/F win
    if(!v_flag) //--- create window if it doesn't exist
        Wave currentframe
        NewImage/N=win currentframe
        ModifyImage/W=win currentframe ctab= {0,65535,Grays,0}
        Controlbar 50
        Slider sldFrame,pos={1,1},size={220,45},limits={0,499,1},value= 0,vert= 0,proc=sliderproc
    else //--- update frame
        //----------------
        //Here I want do do image processing which might be rather lengthy
        //In place of calculations, I sleep
        sleep/T 20
       
        Controlinfo/W=win sldFrame
        ImageTransform/P=(v_value) getplane images
        Wave m_imageplane
        Duplicate/O m_imageplane, currentframe
    endif
End

Function SliderProc(name, value, event) : SliderControl
    String name
    Variable value
    Variable event  // bit field: bit 0: value set; 1: mouse down,
                //   2: mouse up, 3: mouse moved

    NVAR/Z UPDATING_FRAME
    if(!NVAR_EXISTS(UPDATING_FRAME))
        Variable/G UPDATING_FRAME = 0
    endif

    if(UPDATING_FRAME==1)
        return 0
    endif
    UPDATING_FRAME=1
       
    if(event %& 3)
        showimage()
    endif  
   
    UPDATING_FRAME=0
   
    return 0
End