Manipulate keeps updating due to a function

Question

Edit: This is apparently only a problem on a mac running OSX.

I am trying to use the 'stretchText' function by Jens. But when I use it in manipulate, the output keeps updating without changing anything.

This is the simplest example in which the problems occurs:

Manipulate[
 choice;

 Graphics[{
   stretchText["{", {0, 0}, {.1, 1}]
   }],

 {{choice, "b"}, {"a", "b"}},

 Initialization -> {
   stretchText[char_, pos_, scale_, angle_ : 0] := 
     Module[{g, coords, xMin, xMax, yMin, yMax}, 
      g = First@
        First@ImportString[ExportString[char, "PDF"], 
          "TextOutlines" -> True]; 
      coords = 
       Apply[Join, 
        Cases[g, FilledCurve[___, p_] :> Flatten[p, 1], 
         Infinity]]; {{xMin, xMax}, {yMin, yMax}} = 
       Map[{Min[#], Max[#]} &[#] &, Transpose[coords]]; 
      Rotate[Inset[
        Graphics[g, PlotRange -> {{xMin, xMax}, {yMin, yMax}}, 
         If[ListQ[scale], AspectRatio -> Full, 
          AspectRatio -> Automatic]], pos, {xMin, yMin}, scale], 
       angle]];
   }]

What can I do to stop the endless updating?

Answer 1

The problem seems to lie somewhere in some part of the PostScript/PDF conversion system that is tagged for dynamic updating. I'm not sure why it is that way. One workaround is to cache (memoize) the text as it is converted, like this:

Clear[getCurve];
getCurve[s_String] := getCurve[s] = 
   First@First@
     ImportString[ExportString[s, "PDF"], "TextOutlines" -> True];

Manipulate[

 choice;
 stretchText["{", {0, 0}, {.1, 1}, 0], {{choice, "b"}, {"a", "b"}},

 {{stretchText, stretchText}, None}, 
 Initialization :> {stretchText[char_, pos_, scale_, angle_] := 
     Module[{g, coords, xMin, xMax, yMin, yMax, r},
      g = getCurve[char];
      coords = 
       Apply[Join, Cases[g, FilledCurve[_, p_] :> Flatten[p, 1], Infinity]];
      {{xMin, xMax}, {yMin, yMax}} = Map[{Min[#], Max[#]} &[#] &, Transpose[coords]];
      Graphics@
       Rotate[Inset[
         Graphics[g, PlotRange -> {{xMin, xMax}, {yMin, yMax}}, 
          If[ListQ[scale], AspectRatio -> Full, 
           AspectRatio -> Automatic]], pos, {xMin, yMin}, scale], 
        angle]];}]

Edit: There was an unnecessary Dynamic@ in front of stretchText["{",...] I removed.