Re: Consistent Colors

[Devendra Ghate <devendra.ghate@gmail.com>]

On 01/29/2013 01:41 PM, Devendra Ghate wrote:
> I have been going through the concepts underlying pallet.
>
> I would like to define three basic colors in RGB. Then use various shades
> and tints of these basic three colors through out the document.
>
> Now the algorithm for getting various shades for RGB scheme is:
>
> Darker shades:
> Multiply each component by 1/4, 1/2, 3/4, etc.
> of its previous value, depending on how dark the
> color should be.
>
> Lighter tints:
> Calculate (1 - previous value), multiply that by
> 1/4, 1/2, 3/4, etc. and add that to the previous value.
>
> What I would like is a macro that is fed a color name
> and should define 3 shades above and below it.
>
> I have following problems:
>
> 1. How to get RGB values of an already defined color? If this is too 
> involved then
> I can pass the RGB values to the macro as well.
>
> 2. How to create a loop and carry out the above arithmatic to
> create RGB values for various shades?
>
> Essentially the problem boils down to doing arithmetic calculations
> and creating loops in ConTeXt.
>
> Regards,
> Devendra
>
> MWE:
> --------------------------
> \setupcolor[rgb]
> \definecolor[maroon][r=0.8, g=0.2, b=0.4]
>
> %\definecolorgroup
> %[maroon][rgb]
>    %[0.9:0.6:0.7,
>     %0.8:0.2:0.4,
>     %0.4:0.1:0.2,
>     %0.2:0.05:0.1]
>
> % A macro that generates three shades above and below the given color.
> % It is assumed here that the RGB values are also passed along with
> % the color name.
> \define[4]\generateColorGroup{
>   \definecolorgroup
>    [#1]
>    [#2:#3:#4]
>      %\dimexpr#2/4:#3/4:#4/4]
> }%
> \generateColorGroup{maroon}{0.8}{0.2}{0.4}
> \starttext
>  \showcolor
> \stoptext
> -------------------------------
I see now that this is a trivial question. Though I was not able to
use a loop, I used \ctxlua{context(math expr.)} for floating point
arithmetic.

Devendra




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