Re: Feature Request: define colour in relation to existing colour

[Hans Hagen <pragma@wxs.nl>]

On 8/21/2013 2:25 AM, Thangalin wrote:
> Hi,
>
> What would it take to extend \definecolor so that:
>
>    \definecolor[ColourA][ColourB][t=0.5, a=1]
>
> defines a new colour (ColourB) based on an existing colour (ColourA)?
>
> I know that \definespotcolor[ColourA][ColourB][t=0.5, a=1] works, but
> it seems like \definecolor would also be a natural fit.

hm, afaik no one ever needed that (normally one defines colors once on 
top of the document and there are seldom many of them)

anyhow, as general inheritance is pretty fuzzy i.e. cloning a spot color 
and changing some rgb component or cloning a cmyk color and setting rgb 
components it will not be a feature of definecolor

I've added \defineprocesscolor that cna be used as follows:

\starttext

\defineprocesscolor[red][r=.5]

\blackrule[color=red,width=\hsize,height=1cm]

\defineprocesscolor[redish][red][a=1,t=.5]

\blackrule[color=redish,width=\hsize,height=1cm]

\stoptext

But ... as there is some checking of the preferred color space (in 
context each defined color has a preferred color space and there is also 
a current colorspace that gets applied) you need to be aware of this:

\starttext

\defineprocesscolor[red][r=.5]

\blackrule[color=red,width=\hsize,height=1cm]

\defineprocesscolor[redish][red][a=1,t=.5]

\blackrule[color=redish,width=\hsize,height=1cm]

\defineprocesscolor[yellowish][red]

\blackrule[color=yellowish,width=\hsize,height=1cm]

\defineprocesscolor[yellowish][red][a=1,t=.5,y=.5]

\blackrule[color=yellowish,width=\hsize,height=1cm]

\defineprocesscolor[cyan][c=.5]

\defineprocesscolor[yellowish][cyan][y=.5]

\blackrule[color=yellowish,width=\hsize,height=1cm]

\stoptext

Now .. as you requested it, you're also the one who's going to wikify 
it. I'll upload a beta later.

Hans

ps. Transparency operates independently of colors but I never figured 
out a decent way to let that cooperate with existing colors that have 
transparency specs without breaking compatibility so it might never 
happen (in fact we have: current color space, current color, current 
transparency).

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