Graphics and media/Collections of tips and tricks/Use MetaPost arrays

In Metapost (or rather in Metafun) one can define arrays of colors, strings, paths, pens and other variables. An example is the following:

• \starttext
  \startMPpage
  
  string MyColors[] ;
  path   MyPaths [] ;
  pen MyPens[] ;
  for j = -1 step 1 until 3 :
    MyPens[j] := pencircle scaled ((2+j)*pt) ;
  endfor
  
  MyPaths[-1] := (-1.5cm,1.5cm) -- (1.5cm,1.5cm) ; 
  MyColors[-1]:= "magenta" ; 
  MyPaths[0]  := (-2cm,2cm) -- (2*cos(0)*cm,-2cm) ; 
  MyColors[0] := "darkyellow" ;
  MyPaths[1]  := fullcircle scaled 3cm ; 
  MyColors[1] := "darkred" ;
  MyPaths[2]  := fullsquare scaled 2cm ; 
  MyColors[2] := "darkgreen" ;
  MyPaths[3]  := (-2cm,-2cm) -- (2cm,2cm) ; 
  MyColors[3] := "darkblue" ;
  
  for j = -1 step 1 until 3 :
    draw MyPaths[j] 
         withpen MyPens[j] 
         withcolor MyColors[j] ;
  endfor
  \stopMPpage
  \stoptext
  

• 

In the above example, instead of

string MyColors[] ;

one could have said

color MyColors[] ;

and then we should have defined each component of MyColors as colors instead of strings:

• \starttext
  \startMPpage
  color MyColors[] ;
  path   MyPaths [] ;
  pen MyPens[] ;
  for j = -1 step 1 until 3 :
    MyPens[j] := pencircle scaled ((2+j)*pt) ;
  endfor
  
  MyPaths[-1] := (-1.5cm,1.5cm) -- (1.5cm,1.5cm) ; 
  MyColors[-1]:= magenta ; 
  MyPaths[0]  := (-2cm,2cm) -- (2*cos(0)*cm,-2cm) ; 
  MyColors[0] := darkyellow ;
  MyPaths[1]  := fullcircle scaled 3cm ; 
  MyColors[1] := darkred ;
  MyPaths[2]  := fullsquare scaled 2cm ; 
  MyColors[2] := darkgreen ;
  MyPaths[3]  := (-2cm,-2cm) -- (2cm,2cm) ; 
  MyColors[3] := darkblue ;
  
  for j = -1 step 1 until 3 :
    draw MyPaths[j] withpen MyPens[j] withcolor MyColors[j] ;
  endfor
  \stopMPpage
  \stoptext
  

• 

Also note that in order to specify the size of the pen in MyPens[j] we have to say ((2+j)*pt) in order for Metapost to interpret correctly the desired size of the pen. The outer parentheses are to prevent MetaPost from interpreting the definition as

MyPens[j] := (pencircle scaled (2+j)) * pt ;

which would result in an error.