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It appears that the mechanics of the Front End prevent TouchPosition from working as expected. My plan is to keep track of the position of the second touch using TouchPosition["Graphics",2] in the code below. The user would make a first touch on the graph, then write on it with the second touch. However, when I make the second touch and move it, then the zoom factor of the Front End changes, instead of the second touch being tracked. How can I actually track the second touch? By the way, I am using Windows 10 on a Surface laptop.

Code in question:

mymouse := Block[{}, pos = TouchPosition["Graphics",2];
  If[pos =!= None, AppendTo[posList, pos];
   posList = DeleteDuplicates@posList;]]
posList = {};
Dynamic[Graphics[Line@posList, Frame -> True, ImageSize -> Medium, 
  PlotRange -> {{0, 6}, {0, 4}}]]
Dynamic[mymouse]

By contrast, this code works as expected if instead of tracking touch, I track the mouse with pos=MousePosition["Graphics"];.

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    $\begingroup$ What system are you using? (I can't help probably, since I don't have a touchscreen, but it might be important.) $\endgroup$
    – Michael E2
    Commented Jun 8, 2022 at 16:52

1 Answer 1

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TouchPosition and GestureHandler are only supported in Wolfram Player on iOS.

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