[Tex/LaTex] Tikz: Color a region

tikz-pgf

I used the following code to draw a picture. I want to make the region insde (0,7), (0,11),(3,8),(3,4) to be red, and the region above it to be gray, but I don't know how to do this.

\documentclass{article}
\usepackage{tikz}
\begin{document}
\pagestyle{empty}
\begin{tikzpicture}[scale=0.5]

\draw (1.05cm,2pt) node[above];
 %  {$\displaystyle\int_0^{3/2} \!\!x^2\mathrm{d}x$};

\draw[style=help lines] (0,0) grid (3.9,11.9);
  % [step=0.25cm]      (1,2) grid +(1,1);

\draw[->] (-1,0) -- (4,0) node[right] {$i$};
\draw[->] (0,-1) -- (0,12) node[above] {$j$};

\foreach \x/\xtext in {1/1, 2/2, 3/3}
\draw[shift={(\x,0)}] (0pt,2pt) -- (0pt,-2pt) node[below] {$\xtext$};

\foreach \y/\ytext in {1/, 2/, 3/,4/,5/,6/,7/7,8/, 9/, 10/, 11/11}
\draw[shift={(0,\y)}] (2pt,0pt) -- (-2pt,0pt) node[left] {$\ytext$};

\draw  {(0,11) -- (3,8)} node[below right] ;
\draw  {(0,7) -- (3,4)} node[below right] ;
\draw  {(3,8) -- (3,4)} node[below right] ;
\end{tikzpicture}

\end{document}

enter image description here

Best Answer

For the red shape you could try this. I am not sure what you mean by "above" in this case.

\documentclass{article}
\usepackage{tikz}
\begin{document}
\pagestyle{empty}

\begin{tikzpicture}[scale=0.5]

\draw (1.05cm,2pt) node[above]{};
 %  {$\displaystyle\int_0^{3/2} \!\!x^2\mathrm{d}x$};

\draw[style=help lines] (0,0) grid (3.9,11.9);
  % [step=0.25cm]      (1,2) grid +(1,1);

\draw[->] (-1,0) -- (4,0) node[right] {$i$};
\draw[->] (0,-1) -- (0,12) node[above] {$j$};

\foreach \x/\xtext in {1/1, 2/2, 3/3}
\draw[shift={(\x,0)}] (0pt,2pt) -- (0pt,-2pt) node[below] {$\xtext$};

\foreach \y/\ytext in {1/, 2/, 3/,4/,5/,6/,7/7,8/, 9/, 10/, 11/11}
\draw[shift={(0,\y)}] (2pt,0pt) -- (-2pt,0pt) node[left] {$\ytext$};

\draw[fill=red]  (0,11) -- (3,8) -- (3,4) -- (0,7) -- cycle;
\fill[gray!20,nearly transparent] (0,11) -- (0,12) -- (3,12) -- (3,8) -- cycle;
% \fill[gray!20] (0,11) -- (0,12) -- (3,12) -- (3,8) -- cycle; %without transparency
\end{tikzpicture}

\end{document}

red

Instead of nearly transparent you use the opacity key, for example opacity=0.3. See pgfmanual Ch. 20.2 for more details.

Related Solutions

[Tex/LaTex] How to color a region

If you don't mind to have the paths twice in your picture you can use clipping to only draw the inner area. Clipping is local to the scope and accumulates. So you can take the figure as two overlapping "leaves" and clip to both, then fill the whole rectangle.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{intersections,positioning}

\begin{document}

\begin{tikzpicture}[radius=5]
\begin{scope}
\clip (0,0) arc[start angle=-90,end angle=0]   -- (5,5)
            arc[start angle=90,end angle=180]  -- (0,0);
\clip (0,5) arc[start angle=180,end angle=270] -- (5,0)
            arc[start angle=0,end angle=90]    -- (0,5);
\fill [red] (0,0) rectangle (5,5);
\end{scope}
\draw (0,0) rectangle (5,5);
\draw[name path=c1] (0,0) arc[start angle=-90,end angle=0] -- (5,5);
\draw[name path=c2] (5,0) arc[start angle=0,end angle=90] -- (0,5);
\draw[name path=c3] (5,5) arc[start angle=90,end angle=180] -- (0,5);
\draw[name path=c4] (0,5) arc[start angle=180,end angle=270] -- (5,0);
\begin{scope}
\fill [name intersections={of=c1 and c2}]
  (intersection-1) circle (2pt) node[label=right:$A$] {};
\fill [name intersections={of=c2 and c3}]
  (intersection-1) circle (2pt) node[label=above:$B$] {};
\fill [name intersections={of=c3 and c4}]
  (intersection-1) circle (2pt) node[label=left:$C$] {};
\fill [name intersections={of=c4 and c1}]
  (intersection-1) circle (2pt) node[label=below:$D$] {};
\end{scope}
\end{tikzpicture}

\end{document}

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

The source of the difficulty is that ellipses are constructed in a particular way in TikZ. They are paths that start from the x-axis and proceed counter-clockwise around their centre. The vast majority of the time, the exact parametrisation doesn't matter. You appear to have found the one situation where it does!

In the actual question, you only want to be able to mirror the ellipse, and so draw it starting from the negative x-axis (the title of the question suggests a more flexible approach). That's actually not too hard since we can exploit the symmetry of the ellipse. The key is to provide it with a negative x-radius, since then it will start from the negative x-axis (and proceed clockwise, but we could correct for that by negating the y-radius as well). To do this, we interrupt the call from the node shape to the drawing command and flip the sign of the x-radius. The simplest way to do this is to redefine the \pgfpathellipse macro to do the negation and then call the original macro. The following code does this.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations,shapes,decorations.markings}
\makeatletter
\let\origpgfpathellipse=\pgfpathellipse
\def\revpgfpathellipse#1#2#3{%
  #2%
  \pgf@xa=-\pgf@x
  \origpgfpathellipse{#1}{\pgfqpoint{\pgf@xa}{0pt}}{#3}}
\makeatother

\tikzset{
  reversed ellipse/.style={
    ellipse,
    reverse the ellipse%
  },
  reverse the ellipse/.code={
    \let\pgfpathellipse=\revpgfpathellipse
  }
}
\begin{document}
\begin{tikzpicture}
\node[ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,0) {hello world};

\node[reversed ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,-2) {hello world};
\end{tikzpicture}

\end{document}

Here's the result:

rotated ellipse

(the arrow got clipped, but you can see where it lies)

Best Answer

Related Solutions

[Tex/LaTex] How to color a region

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

Related Question