MetaFun - Pragma ADE

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such a feature at a higher abstraction level is not only more portable, but also less sensitive for
misinterpretation.
vardef ColorCircle (expr method, factor, ca, cb, cc) =
save u, p ; path p ; p := fullcircle shifted (1/4,0) ;
image
( fill p rotated 90 withcolor transparent(method,factor,ca) ;
fill p rotated 210 withcolor transparent(method,factor,cb) ;
fill p rotated 330 withcolor transparent(method,factor,cc) )
enddef ;
draw ColorCircle ("normal", .5, red, green, blue) xsized 3cm ;
currentpicture := currentpicture shifted (-4cm,0) ;
draw ColorCircle ("exclusion", .5, red, green, blue) xsized 3cm ;
currentpicture := currentpicture shifted (-4cm,0) ;
draw ColorCircle ("exclusion", 1, red, green, blue) xsized 3cm ;
color xcyan ; xcyan := cmyk(1,0,0,0) ;
color xmagenta ; xmagenta := cmyk(0,1,0,0) ;
color xyellow ; xyellow := cmyk(0,0,1,0) ;
draw ColorCircle ("exclusion", .5, xcyan, xmagenta, xyellow) xsized 3cm ;
You can be tempted to use transparency as a convenient way to achieve soft colors. In that case
you should be aware of the fact that rendering transparent colors takes more time than normal
colors 12
Fortunatey, METAPOST provides a similar mechanism. The last circle in the following row demonstrates
how we can trigger colors proportionally to other colors. Normally background is white,
but you can set predefined color variables to another value.
path p ; p := fullcircle scaled 2cm ;
fill p shifted (0cm,0) withcolor blue ;
When your printer does not support this feature natively, the intermediate (POSTSCRIPT) file send to the printing engine is
also larger.
Special effects Transparency