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I have an icon defined like that:

speakerIcon = Graphics[{
    Triangle[{{0, -1}, {1,1},{-1,1}}],
    Rectangle[{-1, -1},{1, 0}]
}, ImageSize->20]

I can display that icon in an arbitrary color by wrapping it inside Show:

Show[Graphics[FaceForm[Pink]], speakerIcon]

But how to draw only the outline of the icon? Using EdgeForm does not work since it displays the outline of each component of the graphic object:

Show[
    Graphics[FaceForm[]],
    Graphics[EdgeForm[{Thick,Blue}]], 
    speakerIcon, ImageSize->100
]

enter image description here

FWIW, I suspect I didn't follow the "right" path by defining my region as a Graphics. Maybe using Region would have been better? I'm open to any suggestions.

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2 Answers 2

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With Mathematica 12 a possible approach is OuterPolygon: 

pol = Polygon[{{{0, -1}, {1, 1}, {-1, 1}}, {{-1, -1}, {1, -1}, {1, 
     0}, {-1, 0}}}]
Graphics[{FaceForm[], EdgeForm[{Thick, Blue}], pol}]

enter image description here

Graphics[{FaceForm[], EdgeForm[{Thick, Blue}], OuterPolygon[pol]}]

enter image description here

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  • $\begingroup$ Merci beaucoup André! I still have to try it, but I think I will follow that path (pun intended) because, as I explained in a comment to the @kglr's answer, I'm somewhat uncomfortable in constantly converting from graphics to regions and back. $\endgroup$
    – Sylvain Leroux
    Feb 24, 2020 at 11:55
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You can use BoundaryDiscretizeGraphics:

bdg = BoundaryDiscretizeGraphics @ speakerIcon

enter image description here

Graphics[{EdgeForm[{Black, Thin}], FaceForm[], MeshPrimitives[bdg, 2]}, ImageSize -> 30]

enter image description here

Alternatively, you can use BoundaryDiscretizeRegion + RegionUnion:

bdr = BoundaryDiscretizeRegion[
  RegionUnion[Triangle[{{0, -1}, {1, 1}, {-1, 1}}], Rectangle[{-1, -1}, {1, 0}]]]

enter image description here

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  • $\begingroup$ Thanks, @kglr. One side comment: when drawing shapes, I noticed I often have to convert between Graphics objects and Region, in one direction or the other. I read regions are a recent addition to Mathematica. Does that mean a rule of thumb would be to use them exclusively and considering Graphics only to render the output? On the other hand, it seems quite a waste of resources to convert even the simplest polygons to mesh objects. $\endgroup$
    – Sylvain Leroux
    Feb 24, 2020 at 11:51
  • 1
    $\begingroup$ @SylvainLeroux, TIL from andre's answer that it may not be necessary to go through Region for some shapes. $\endgroup$
    – kglr
    Feb 24, 2020 at 17:54

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