Drawing a box with shading in pgfplots

Question

As a follow-up to this question, or more precisely this answer, I'd like to know how to do the equivalent of

\shadedraw
  [shading=axis,left color=green,right color=orange,color=blue,line width=2] 
  (2,0) -- (2,1) 
  {[rounded corners=1em] -- (3,1)} --
  (3,0) -- (2,0);

using pgfplots such that the shading is done in the CMYK colorspace.

(This would then be used in baposter as a replacement for the shading in the headers of the boxes.)

May I ask why you insist on CMYK model for a poster? You can ask for the CMYK version from the printer if you feel there will be a significant difference. In Photoshop (if you have it) there was a Gamut Warning thingy when I was keen on using Adobe stuff. That can tell you if there will be a significant problem by turning the areas in the gray. — percusse, Oct 10 '13 at 08:43
The reason is that I have a shading from white to light gray in the background. I cannot predict what this would look like in print if it's converted from RGB to CMYK, so I'd prefer to use CMYK. — fuenfundachtzig, Oct 10 '13 at 10:17

score 7 · Accepted Answer · edited Apr 13 '17 at 12:35

As already stressed in https://tex.stackexchange.com/a/137031, this answer should be considered a workaround: the correct solution would be to "wait for the feature request in tikz".

Naturally, that can take longer than having a clumsy work-around at hand.

Here is an attempt to use a pgfplots surface plot to simulate your desired filled shading:

enter image description here

\documentclass[a4paper]{article}

\usepackage[cmyk]{xcolor}

\usepackage{pgfplots}
\pgfplotsset{compat=1.9}
% if you have v1.8, write:
%\pgfplotsset{mesh/colorspace explicit color output=cmyk}


\begin{document}

\begin{tikzpicture}
\draw (0,0) grid (3,3);
    \shadedraw
  [shading=axis,left color=green,right color=orange,color=blue,line width=2] 
  (2,0) -- (2,1) 
  {[rounded corners=1em] -- (3,1)} --
  (3,0) -- (2,0);
\end{tikzpicture}

\begin{tikzpicture}

\draw (0,0) grid (3,3);
    \draw
  [color=blue,line width=4pt] 
  (2,0) -- (2,1) 
  {[rounded corners=1em] -- (3,1)} --
  (3,0) -- cycle;
    \clip
  (2,0) -- (2,1) 
  {[rounded corners=1em] -- (3,1)} --
  (3,0) -- cycle;

    \begin{axis}[
        % necessary to match up coordinate systems:
        xmin=0,ymin=0,
        anchor=origin,
        x=1cm,y=1cm,
        hide axis,
    ]
    \addplot[surf,mesh/color input=explicit,shader=interp] 
    table[meta=cdata] {
        x y cdata
        2 0 color=green
        2 1 color=green

        3 0 color=orange
        3 1 color=orange
    };
    \end{axis}
\end{tikzpicture}
\end{document}

Both are tikzpictures, the first one is replicated from your question and the second one is based on pgfplots. You see that it is considerably more involved: it installs a clip path to restrict the shading to your "rounded" rectangle, then it draws the outline of the clip path (for some reason, pgf rejects it if I say \draw[clip] with the remaining options). The rest is a pgfplots axis which is forced to use the same coordinate system as the outer tikz picture (requiring a bunch of keys explained in section "TikZ interoperability" in the pgfplots manual).

This answer will hopefully become superfluos once TikZ supports CMYK shadings.

As the feature request is almost 6 years old, I have little hope this will ever be implemented. Thus thanks a lot for your workaround. — fuenfundachtzig, Oct 11 '13 at 18:14
Actually, I considered implementing the TikZ driver... it is not particularly difficult. But I'm glad the workaround helps. The message was more for others than for you. — Christian Feuersänger, Oct 12 '13 at 06:55

Drawing a box with shading in pgfplots

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