[metapost] rfc: consistent color values
taco at elvenkind.com
Fri Apr 8 14:39:56 CEST 2005
Hans Hagen wrote:
> Jens-Uwe Morawski wrote:
>> Since Taco told about a MP 1.0 release later this year, IMO
>> the following problem should be discussed before.
>> In the example below you can see that MP replaces
>> silently all negative color values with 0.
First, to make sure Hans is not misinterpreting the report:
this replacement happens at the 'addto' stage, not earlier,
so Hans' example:
color diminish ; diminish := (-.5,-.2,.-3) ;
... withcolor (red+diminish);
works ok, it would report:
This also works:
color diminished; diminished = (red+diminish);
There is only a problem when one tries to access the
colors within an already drawn picture, not when there
is still a 'color type'.
>> IMO MP should either disallow negative color values
>> (err message) or should not change the values
>> to 0 as long as the values are accessible on macro level
>> (before shipout).
It looks like this can be classified as an oversight (bug),
because the documented behaviour is:
"... all components are snapped back to the [0, 1] range
when a color is given in a PostScript output file."
so clearly the picture iteration should have reported the
values with their negative components still intact.
>> Is this possible to change? Makes it sense?
I believe this is a bug (because the actual documentation makes
no mention of picture variables), so I think a fix is needed.
I will add this to the bug database, to be fixed for v1.0.
Thanks for the report,
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