[Tex/LaTex] How to use shading in TikZ when rotating the picture

pdftextikz-pgf

I have the following problem: I want to draw a rectangle and around it, there should be some smooth fading to the background (white). I found the shading technique of tikz quite interesting. The problem is, that it does not behave as I suspect. See the following example:

\documentclass{minimal}
\usepackage{tikz}
\usetikzlibrary{scopes,fadings}
\begin{document}
\begin{tikzpicture}
  \shade [top color=white,bottom color=red,shading angle=90] (-1,-1) rectangle (1,1);
  \filldraw [color=red,xshift=2cm] (-1,-1) rectangle (1,1);
  \shade [top color=red,bottom color=white,shading angle=90,xshift=4cm] (-1,-1) rectangle (1,1);
  { [ xshift=10cm,rotate=-30]
    \shade [top color=white,bottom color=red,shading angle=60] (-1,-1) rectangle (1,5);
    \filldraw [color=red,xshift=2cm] (-1,-1) rectangle (1,5);
    \shade [top color=red,bottom color=white,shading angle=60,xshift=4cm] (-1,-1) rectangle (1,5);
  }
\end{tikzpicture}
\end{document}

I for me get using pdflatex two blocks. The left is drawn correctly but (clearly) not rotated. In the right picture the colors at the ends of the fadings are not set correctly: I can see a difference between the white background and the nearly white upper left end. Also in the middle at the conjunction with the red square the color is not correct.

Can you tell me what I am doing wrong?

Best Answer

The problem is that the figures get rotated first and then the shading is applied; to obtain the desided effect, you can apply a canvas transformation (See Section 22.4 Canvas Transformations of the pgf manual):

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{scopes,fadings}

\begin{document}
\begin{tikzpicture}[transform canvas={rotate=-30}]
    \shade [top color=white,bottom color=red,shading angle=60] (-1,-1) rectangle (1,5);
    \filldraw [color=red,xshift=2cm] (-1,-1) rectangle (1,5);
    \shade [top color=red,bottom color=white,shading angle=60,xshift=4cm] (-1,-1) rectangle (1,5);
\end{tikzpicture}

\end{document}

enter image description here

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[Tex/LaTex] get an extra white page before the TikZ picture

use

\begin{landscape}
\resizebox{!}{0.95\textheight}{\input{erd.tikz.tex}}
\end{landscape}

The image is too big. The reason why it is placed on the following page.

[Tex/LaTex] TikZ: Drawing an arc from an intersection to an intersection

A solution which allows to draw intersection segments of any two intersections is available as tikz library fillbetween.

This library works as general purpose tikz library, but it is shipped with pgfplots and you need to load pgfplots in order to make it work:

\documentclass{standalone}

\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{fillbetween}

\begin{document}

\begin{tikzpicture}

\draw [name path=red,red] (120:1.06) circle (1.9);
%\draw [name path=yellow,yellow] (0:1.06) circle (2.12);
\draw [name path=green,green!50!black] (0:0.77) circle (2.41);
\draw [name path=blue,blue] (0:0) circle (1.06);

% substitute this temp path by `\path` to make it invisible:
\draw[name path=temp1, intersection segments={of=red and blue,sequence=L1}];
\draw[red,-stealth,ultra thick, intersection segments={of=temp1 and green,sequence=L3}];

\end{tikzpicture}

\end{document}

enter image description here

The key intersection segments is described in all detail in the pgfplots reference manual section "5.6.6 Intersection Segment Recombination"; the key idea in this case is to

create a temporary path temp1 which is the first intersection segment of red and blue, more precisely, it is the first intersection segment in the Left argument in red and blue : red. This path is drawn as thin black path. Substitute its \draw statement by \path to make it invisible.
Compute the desired intersection segment by intersecting temp1 and green and use the correct intersection segment. By trial and error I figured that it is the third segment of path temp1 which is written as L3 (L = left argument in temp1 and green and 3 means third segment of that path).

The argument involves some trial and error because fillbetween is unaware of the fact that end and startpoint are connected -- and we as end users do not see start and end point.

Note that you can connect these path segments with other paths. If such an intersection segment should be the continuation of another path, use -- as before the first argument in sequence. This allows to fill paths segments:

\documentclass{standalone}

\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{fillbetween}

\begin{document}

\begin{tikzpicture}

\draw [name path=red,red] (120:1.06) circle (1.9);
%\draw [name path=yellow,yellow] (0:1.06) circle (2.12);
\draw [name path=green,green!50!black] (0:0.77) circle (2.41);
\draw [name path=blue,blue] (0:0) circle (1.06);

% substitute this temp path by `\path` to make it invisible:
\draw[name path=temp1, intersection segments={of=red and blue,sequence=L1}];
\draw[red,fill=blue,-stealth,ultra thick, intersection segments={of=temp1 and green,sequence=L3}]  
    [intersection segments={of=temp1 and green, sequence={--R2}}]
;

\end{tikzpicture}

\end{document}

enter image description here

Best Answer

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[Tex/LaTex] get an extra white page before the TikZ picture

[Tex/LaTex] TikZ: Drawing an arc from an intersection to an intersection

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