mirror figure in metapost

Question

With a valid figure, I would like to always produce the mirror figure. To clarify my thought, I'm looking for some tricks to do something like:

beginfig(1);
  ...
endfig;

beginfig(2);
  mirror(fig1);
endfig;

Is such a thing possible ?

Answer 1

picture keep;
beginfig(1);

... Metapost code ...

keep:=currentpicture;
endfig;

beginfig(2);
z1=.5[llcorner keep,lrcorner keep];
z2=.5[ulcorner keep,urcorner keep];
currentpicture:=keep reflectedabout (z1,z2);
endfig;
end

Before shipping out the first figure, we keep it into a picture variable. The operators llcorner and so on allow access at the bounding box of a picture.

A similar trick is used in manfnt.mf to draw the mirror image of the dangerous bend symbol (see the definitions of characters 127 and 126).