Wolfram Technology Guide: Symbolic Interface Construction  previous | next 
Create Locator-Based Interfaces
Mathematica lets you create interfaces based on arbitrary movable "locators".
In[1]:=

Click for copyable input
Manipulate[

 Graphics[{LightRed, Polygon[p[[Last[FindShortestTour[p]]]]]}, 

  PlotRange -> {{-1, 1}, {-1, 1}}],

 {{p, RandomReal[{-1, 1}, {15, 2}]}, Locator}]
Out[1]=