How to create a blinking image marker?

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I have a 2-D image graph, and want to put a blinking marker on the display. This marker should be relatively small, and blink as rapidly as possible (up to 4 Hz) for ease of perception. My approach has been to use a drawing object, and get it to update as rapidly as possible. I have tried to adapt one method described in the IP manual, but have not succeeded in my goals. I am hoping someone can show me where I am going wrong, or suggest an alternate approach. The code shown clears the old marker, shows a new marker, but does not blink further, even though the loop has five iterations. The only marker attribute that needs to change is from fillfgc=(....) with specified colors, to fillpat=0 (transparent). An alternative would be to remove and redraw the marker, but I had no better luck with that.
function drawdot(x,y, contrast)
    variable x, y, contrast
    variable ticks0,  j
    variable color = 65535/2 + contrast*65535/2    //   sets the blinker contrast in the autoscaled image
    SetDrawLayer /W=Graph2/K  UserFront           //    clear old draw objects
    SetDrawLayer /W=Graph2 UserFront
    
    for(j=0;j<5;j+=1)   //  blink loop
         SetDrawEnv gstart, gname = greydot
         SetDrawEnv xcoord= bottom,ycoord= left,fillfgc= (color,color,color),linethick= 0.00
         DrawOval /W=Graph2  x, y, x-0.02, y-0.02   //  a variable greyscale fill pattern
         SetDrawEnv gstop
         DoUpdate/W=Graph2
    
         ticks0 = ticks
         do
         while( (ticks-ticks0)<60 ) //  delay one second, for example
        
         DrawAction getgroup=greydot, delete, begininsert
         SetDrawEnv gstart, gname = greydot
         SetDrawEnv xcoord= bottom,ycoord= left,fillpat=0 ,linethick= 0.00 // no fill
         DrawOval /W=Graph2  x, y, x-0.02, y-0.02     // effectively invisible
         SetDrawEnv gstop
         DrawAction endinsert
         DoUpdate/W=Graph2
    
         ticks0 = ticks
         do
         while( (ticks-ticks0)<60 )
    endfor
end
I see some overall problems with your function but let's start with the main problem. You were simply putting too much good intention into the redrawing part. :)
Just delete the second drawing part in your for-loop and it works. Drawing and deleting is enough to let the dot blink.

Next, some suggestions:
1) You'd rather use the nifty function 'sleep' for the delay. No need for empty do-while-loops.
2) In the current state the function is extremely hard-coded to a specific case (graph named 'graph2' with bottom and left axes, also the dot size is very dependent on the axis range), but I guess you don't mind. It wouldn't be too difficult to fetch all this data for a more general approach, though (e.g. bringing the desired window to the front at start to omit all these /W flags)
3) You want the dot to blink only five times? How about forever or until something happens? You may want to read more about background functions then.

Here's my reworked function, by the way:
function drawdot(x,y, contrast)
    variable x, y, contrast
    variable j, color = 65535/2 + contrast*65535/2  // sets the blinker contrast in the autoscaled image
    SetDrawLayer/K  UserFront           // clear old draw objects
    SetDrawLayer UserFront
 
    for(j=0;j<5;j+=1)               // blink loop
        SetDrawEnv gstart, gname = greydot
        SetDrawEnv xcoord= bottom,ycoord= left,fillfgc= (color,color,color),linethick= 0.00
        DrawOval   x, y, x-0.02, y-0.02     // a variable greyscale fill pattern
        SetDrawEnv gstop
 
        DoUpdate
        Sleep/S 1
        DrawAction getgroup=greydot, delete, begininsert
        DoUpdate
        Sleep/S 1
    endfor
end

February 2, 2012 at 09:31 am - Permalink
Chozo,
Thanks for your timely and helpful response and suggestions. Your code works well. I have elected to stay with the 'ticks' timing option because the 'sleep' documentation suggests it is best suited for longer intervals rather than fractions of a second (maybe I am wrong there). I have gotten the marker display to blink at about 10Hz.

February 2, 2012 at 10:56 am - Permalink
[quote=s.r.chinn]I ... want to put a blinking marker on the display. ...[/quote]

Had you been from across the pond, we might have responded to this differently. :-)

--
J. J. Weimer
Chemistry / Chemical & Materials Engineering, UAHuntsville

February 2, 2012 at 12:07 pm - Permalink