[Tex/LaTex] Tikz: Draw a RGB cube

colortikz-3dtikz-pgf

I am trying to draw a RGB cube using Tikz. Until now I managed to create this cube with color gradients:

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{3d}
\usetikzlibrary{shadings}
\definecolor{mypurple}{rgb}{1.0,0.0,1.0}
\begin{document}

    \begin{tikzpicture}[x  = {(0.5cm,0.5cm)},
    y  = {(0.95cm,-0.25cm)},
    z  = {(0cm,0.9cm)}]
    \begin{scope}[canvas is yz plane at x=-1]
    \shade[lower right=mypurple, lower left=blue, upper right=white, upper left=cyan] (-1,-1) rectangle (1,1);
    \end{scope}
    \begin{scope}[canvas is xz plane at y=1]
    \shade[lower right=red, lower left=mypurple, upper right=yellow, upper left=white] (-1,-1) rectangle (1,1);
    \end{scope}
    \begin{scope}[canvas is yx plane at z=1]
    \shade[lower right=white, lower left=cyan, upper right=yellow, upper left=green] (-1,-1) rectangle (1,1);
    \end{scope}
    \end{tikzpicture}
\end{document}

Result:

It seems that the reference points upper/lower left/right are interpreted to be relative to the bounding rectangle of the particular rectangle.

How can I set the corners as reference points?

Best Answer

Unfortunately, you can't, as the manual states

This shading fills a rectangle with colors that a bilinearly interpolated between the colors in the four corners of the rectangle.

Here, rectangle seems to mean "a shape whose sides are parrallel to the page's edges". Fortunately, you can interpolate the shading yourself.

A few hints:

I used \colorlet{<name>}[<model>]{<definition>}. If you leave out the <model>, then sometimes a different model is chosen resulting in strange color effects.
The tiles are drawn slightly bigger than they should (the (\x+0.1) and (\y+0.1) parts in the second coordinates). If you use the exact size you'll see tiny gaps between the tiles. That's also why I added a \clip at the beginning of each scope as otherwise the faces would be to big.
It's quite slow for better resolutions. If you use it in a regularly changing document, consider using the externalize facilities.
The code between \makeatletter and \makeatother fix a bug in the implementation of canvas is xy plane at z= of the 3d library. This patch was written by Jake in this answer

Code

\documentclass[tikz, border=2mm]{standalone}
\usetikzlibrary{3d}
\usetikzlibrary{shadings}
\definecolor{mypurple}{RGB}{255,0,255}

\makeatletter
    \tikzoption{canvas is xy plane at z}[]%
    {   \def\tikz@plane@origin{\pgfpointxyz{0}{0}{#1}}%
        \def\tikz@plane@x{\pgfpointxyz{1}{0}{#1}}%
        \def\tikz@plane@y{\pgfpointxyz{0}{1}{#1}}%
        \tikz@canvas@is@plane
    }
\makeatother 

\begin{document}

\pgfmathtruncatemacro{\Divisions}{50}
\pgfmathsetmacro{\Cube}{5}

\begin{tikzpicture}
[   x={(0.5cm,0.5cm)},
    y={(0.95cm,-0.25cm)},
    z={(0cm,0.9cm)}
]
    \begin{scope}[canvas is yz plane at x=-\Cube/2]
        \shade[lower right=mypurple, lower left=blue, upper right=white, upper left=cyan] (-1,-1) rectangle (1,1);
        \clip (-\Cube/2,-\Cube/2) rectangle (\Cube/2,\Cube/2);
        \colorlet{BL}[RGB]{blue}
        \colorlet{BR}[RGB]{mypurple}
        \colorlet{TL}[RGB]{cyan}
        \colorlet{TR}[RGB]{white}
        \foreach \x in {1,...,\Divisions}
        {   \pgfmathtruncatemacro{\px}{(\x-1)/(\Divisions-1)*100}
            \colorlet{B}[RGB]{BR!\px!BL}
            \colorlet{T}[RGB]{TR!\px!TL}
            \foreach \y in {1,...,\Divisions}
            {   \pgfmathtruncatemacro{\py}{(\y-1)/(\Divisions-1)*100}
                \fill[T!\py!B] ({-\Cube/2+\Cube*(\x-1)/\Divisions},{-\Cube/2+\Cube*(\y-1)/\Divisions}) rectangle ({-\Cube/2+\Cube*(\x+0.1)/\Divisions},{-\Cube/2+\Cube*(\y+0.1)/\Divisions});
            }
        }
        \draw[thick] (-\Cube/2,-\Cube/2) rectangle (\Cube/2,\Cube/2);
    \end{scope}

    \begin{scope}[canvas is xz plane at y=\Cube/2]
        \clip (-\Cube/2,-\Cube/2) rectangle (\Cube/2,\Cube/2);
        \colorlet{BL}[RGB]{mypurple}
        \colorlet{BR}[RGB]{red}
        \colorlet{TL}[RGB]{white}
        \colorlet{TR}[RGB]{yellow}
        \foreach \x in {1,...,\Divisions}
        {   \pgfmathtruncatemacro{\px}{(\x-1)/(\Divisions-1)*100}
            \colorlet{B}[RGB]{BR!\px!BL}
            \colorlet{T}[RGB]{TR!\px!TL}
            \foreach \y in {1,...,\Divisions}
            {   \pgfmathtruncatemacro{\py}{(\y-1)/(\Divisions-1)*100}
                \fill[T!\py!B] ({-\Cube/2+\Cube*(\x-1)/\Divisions},{-\Cube/2+\Cube*(\y-1)/\Divisions}) rectangle ({-\Cube/2+\Cube*(\x+0.1)/\Divisions},{-\Cube/2+\Cube*(\y+0.1)/\Divisions});
            }
        }
        \draw[thick] (-\Cube/2,-\Cube/2) rectangle (\Cube/2,\Cube/2);
    \end{scope}

    \begin{scope}[canvas is xy plane at z=\Cube/2]
        \clip (-\Cube/2,-\Cube/2) rectangle (\Cube/2,\Cube/2);
        \colorlet{BL}[RGB]{cyan}
        \colorlet{BR}[RGB]{green}
        \colorlet{TL}[RGB]{white}
        \colorlet{TR}[RGB]{yellow}
        \foreach \x in {1,...,\Divisions}
        {   \pgfmathtruncatemacro{\px}{(\x-1)/(\Divisions-1)*100}
            \colorlet{B}[RGB]{BR!\px!BL}
            \colorlet{T}[RGB]{TR!\px!TL}
            \foreach \y in {1,...,\Divisions}
            {   \pgfmathtruncatemacro{\py}{(\y-1)/(\Divisions-1)*100}
                \fill[T!\py!B] ({-\Cube/2+\Cube*(\x-1)/\Divisions},{-\Cube/2+\Cube*(\y-1)/\Divisions}) rectangle ({-\Cube/2+\Cube*(\x+0.1)/\Divisions},{-\Cube/2+\Cube*(\y+0.1)/\Divisions});
            }
        }
        \draw[thick] (-\Cube/2,-\Cube/2) rectangle (\Cube/2,\Cube/2);
    \end{scope}
\end{tikzpicture}

\end{document}

Output

Related Solutions

[Tex/LaTex] Numerical conditional within tikz keys

I am definitely unfamiliar with both beamer and tikz (do not quite get what the \only are supposed to do) but perhaps this could go in the direction you want:

\documentclass{beamer}
\usepackage{tikz}
\usetikzlibrary{chains}
\newcounter{count}

% helper macro:
\long\def\GobToSemiColon #1;{}

\newcommand\myPicture{
\begin{tikzpicture}
  \begin{scope}[start chain = going below]
  \ifnum\value{count}<1 \expandafter\GobToSemiColon\fi
  \ifnum\value{count}>3 \expandafter\GobToSemiColon\fi
  \node[draw, rectangle, on chain] {display only when counter is between
    1 and 3};

  \ifnum\value{count}>-1 \expandafter\GobToSemiColon\fi
  \node[draw, rectangle, on chain] {display only when counter is
    negative}; 

  \ifnum\value{count}<100 \expandafter\GobToSemiColon\fi
  \ifnum\value{count}>200 \expandafter\GobToSemiColon\fi  
  \node[draw, rectangle, on chain] {display only if counter is between
    100 and 200};

  \ifnum\value{count}<3 \expandafter\GobToSemiColon\fi
  \ifnum\value{count}>20 \expandafter\GobToSemiColon\fi
  \node[draw, circle, on chain] {only when counter is in the range 3 to 20};
  \end{scope}
\end{tikzpicture}
}

\begin{document}
\begin{frame}
\only{\setcounter{count}{-3}\myPicture}
\only{\setcounter{count}{105}\myPicture}
\only{\setcounter{count}{39}\myPicture}
\only{\setcounter{count}{2}\myPicture}
\only{\setcounter{count}{5}\myPicture}
\end{frame}
\end{document}

beamer

[Tex/LaTex] Line up nested tikz enviroments or how to get rid of them

As is explained in How do I draw shapes inside a tikz node? pics can be used for defining new objects. My main problem using pics is how to place where you want because they aren't nodes and positioning them is not so easy.

Following code shows how to define EDFA block.

    EDFA/.pic={
        \begin{scope}[scale=.5]
        \draw (-1,0) coordinate (in) --  (-1,1) -- (1,0) coordinate (out) --  (-1,-1) -- cycle;
        \node[anchor=north,inner sep=2pt] at (0,-1) {$1$};
        \end{scope}

In this case, coordinate (-1,0) will act as west anchor and 1,0 as east. Both point will have an special name for further reference. Every pic is placed according its own origin (0,0). You can use Claudio's answer to Anchoring TiKZ pics for better positioning.

As your example was simple, I'd prefer to star with EDFA and place Source and Sink after it.

\documentclass[]{article}

% tikz
\usepackage{tikz}
\usetikzlibrary{positioning} %relative positioning

\begin{document}

\tikzset{%
    EDFA/.pic={
        \begin{scope}[scale=.5]
        \draw (-1,0) coordinate (in) --  (-1,1) -- (1,0) coordinate (out) --  (-1,-1) -- cycle;
        \node[anchor=north,inner sep=2pt] at (0,-1) {$1$};
        \end{scope}
    }
}

\begin{tikzpicture}[
block/.style={draw},
]

\draw pic (edfa) {EDFA};

\node[block, left=of edfain] (source) {Source};

\node[block, right= of edfaout] (sink) {Sink};

\draw[->] (source) -- (edfain);
\draw[->] (edfaout) -- (sink);

\end{tikzpicture}

\end{document}

I understand that your components are more complex than EDFA because for this particular case an isosceles triangle node with a label will do the work and it can be used as a node and not as a pic:

\documentclass[]{article}

% tikz
\usepackage{tikz}
\usetikzlibrary{positioning} %relative positioning
\usetikzlibrary{shapes.geometric}

\begin{document}

\begin{tikzpicture}[
    block/.style={draw},
    edfa/.style={isosceles triangle, minimum width=1cm, 
         draw, anchor=west, isosceles triangle stretches, 
         minimum height=1cm, label=-80:#1}
]

\node[block] (source) {Source};

\node[edfa=1, right=of source] (edfa) {};

\node[block, right= of edfa] (sink) {Sink};

\draw[->] (source) -- (edfa);
\draw[->] (edfa) -- (sink);

\end{tikzpicture}

\end{document}