MetaFun - Pragma ADE

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These circles were drawn using:
colorcircle(4cm,(.4,.6,.8),(.4,.8,.6),(.6,.4,.8)) ;
addto currentpicture also inverted currentpicture shifted (5cm,0) ;
When we draw a path, or stroke a path, as it is called officially, we actually perform an addition:
addto currentpicture doublepath somepath
The fill command is actually:
addto currentpicture contour somepath
We will need both doublepath and contour operations in the definition of inverted.
When METAPOST has digested a path into a picture, it keeps track of some characteristics. We can
ask for them using part... operators. The following operators can be applied to a transform
vector (one of METAPOST's data types), but also to a picture. Say that we have drawn a circle:
draw fullcircle
xscaled 3cm yscaled 2cm
dashed dashpattern(on 3mm off 3mm)
withpen pencircle scaled 1mm
withcolor .625red ;
picture p ; p := currentpicture ;
This circle looks like:
We can now ask for some of the characteristics of currentpicture, like its color. We could write
the values to the log file, but it is more convenient to put them on paper.
label.rt("redpart: " & decimal redpart p, (4cm,+.5cm)) ;
label.rt("greenpart: " & decimal greenpart p, (4cm, 0cm)) ;
label.rt("bluepart: " & decimal bluepart p, (4cm,-.5cm)) ;
A few more details Analyzing pictures