MetaFun - Pragma ADE

Figure 13.4 Koffka's examples of manipulating
contrast by changing the spatial configuration.
fill unitsquare xyscaled (-width,height) withcolor rightshade ;
draw (fullcircle scaled radius) shifted (0,height/2)
withpen pencircle scaled (radius/2) withcolor centershade ;
\stopuseMPgraphic
The graphics of the second row extend those of the first by drawing a white line through the
middle. In this example setting the linecap is not really needed, because rounded top and bottoms
in white are invisible and the part that extends beyond the points does not count in calculating
the bounding box.
\startuseMPgraphic{second}
\includeMPgraphic{first}
interim linecap := butt ; pickup pencircle scaled gap ;
draw (0,0) -- (0,height) withcolor white ;
\stopuseMPgraphic
The third row graphics again extend the first graphic. First we copy the picture constructed so far.
Watch the double assignment. Next we clip the pictures in half, and shift the right half down over
the width of the circle.
\startuseMPgraphic{third}
\includeMPgraphic{first}
picture p, q ; p := q := currentpicture ;
clip p to unitsquare xscaled width yscaled height ;
clip q to unitsquare xscaled -width yscaled height ;
currentpicture := p ;
Fool yourself A few applications
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