[metapost] background and non-rgbcolors

[Stephan Hennig]

Hi,

the internal variable background seems only to accept rgbcolor values
(which is not documented).  Would it be possible to make 'background'
accept cmykcolor or greyscale values as well?

Another option were to introduce a new macro 'setUnfillColor' that
accepts different colour types and is evaluated by 'unfill'.  For
compatibility 'background' should take precedence over 'setUnfillColor',
by default.  As soon as 'setUnfillColor' has been called with a valid
colour it should overrule 'background'.  Calling 'unfillcolor' with a
special value (e.g., any string value) should return 'unfill' to
compatibility behaviour, i.e., evaluate variable 'background' only.

Best regards,
Stephan Hennig


background := red;% RGB
% background := (1,0,0,0);% CMYK
% background := .5;% greyscale
% background := false;% withoutcolor
beginfig(1);
  unfill unitsquare scaled 100;
endfig;
end

PS:  I'm especially interested in drawing the background without any
colour, i.e., ignoring 'unfill' operations performed by package MetaObj.