Graphics and media/Collections of tips and tricks/Fill-unfill or even-odd rule in Metafun

Metapost doesn't support even-odd rule filling so it uses a fake unfilling via a background color. This is problematic in cases when one deals with e.g. transparency. To overcome this difficulty, Metafun implements some extensions, such as eofill. To fill a shape using the even-odd rule we need a sequence of nofill ending with a eofill statement, as it can be seen in the following examples.

Some examples

• %Adapted from Metafun's manual
  \startMPpage
  nofill fullsquare scaled 2cm ;
  nofill fullsquare scaled 2cm 
         shifted (1cm,0) ;
  eofill fullsquare scaled 2cm 
         shifted (0,1cm) withcolor darkred;
  \stopMPpage
  

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• \startMPpage
      path A; A := (unitcircle 
                    shifted (-center unitcircle)) 
                    scaled 4cm;
      path B; B := (unitcircle 
                    shifted (-center unitcircle)) 
                    scaled 1cm;
      path C; C := B shifted (left*1.4cm);
      nofill A; nofill B; 
      eofill C withcolor darkblue;
  \stopMPpage
  

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