How to get Mathematica to trigger an event when a variable inside a Dynamic[] changes?

I want Mathematica to Beep[] when the colour of a pixel on the screen changes. I recommend wiggling some multicolour window in the middle of the screen to test this program. On Mac you can find the coordinates of pixels at the cursor with Command+Shift+4.

<< GUIKit`;
num := Evaluate[numb[thePixel]];
thePixel := GUIScreenShot[{{1280, 1281}, {730, 731}}];
numb = Flatten[ImageData[#, "Byte"]] &;

        z := num // Total;

        UpdateInterval -> .1

Now you should see a number changing as you change the colours of the pixel.

Now how do I get Mathematica to trigger a Beep[] when the number changes?

clues welcome :)

I tried both of the solutions in Detecting changes of variables' values


1 Answer 1


Maybe this way

Dynamic[Refresh[trigger = Total[numb[thePixel]], UpdateInterval -> 0.1, TrackedSymbols :> {}]]
Dynamic[Refresh[trigger; Beep[]; event, TrackedSymbols :> {trigger}]]

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