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I have some TikZ code of which I would like to widen the bottom part of the output while preserving the width of the top. (Bad formulation, don't know how to formulate this well.)

For example, say I have some square like

\documentclass[tikz]{standalone}
\begin{document}
\begin{tikzpicture}

% Not my actual code snippet, but for simplicity, let's just draw a square
\draw (-1, -1) -- (1, -1) -- (1, 1) -- (-1, 1) -- cycle;


\end{tikzpicture}
\end{document}

Now, for this simple example, it is easy to widen the base of the output by simply drawing an isosceles trapezoid instead of a square like

\documentclass[tikz]{standalone}
\begin{document}
\begin{tikzpicture}

% The top's width is preserved, while the bottom's width is stretched
\draw (-2, -1) -- (2, -1) -- (1, 1) -- (-1, 1) -- cycle;


\end{tikzpicture}
\end{document}

However, for more complex code snippets, this not accessible for me.

How can I transform a generic rectangular-like shape input into a isosceles trapezoid-like shape output? Could the scope environment be of use?

Stephen
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aahlback
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  • I don't understand the problem, if you need a trapezium just draw one (or use the shape trapezium if applicable). What do you mean with “more complex code snippets”? What's not accessible to you? As I see it a transformation that transform a rectangle into a trapezium is non-linear and that's no fun in TikZ. – Qrrbrbirlbel Sep 05 '23 at 11:42
  • By the way, your second example is a triangle (which can be considered a trapezium, sure). – Qrrbrbirlbel Sep 05 '23 at 11:44
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    Maybe related: Perspective transform – dexteritas Sep 05 '23 at 12:04
  • @Qrrbrbirlbel Sorry for not being clear enough, I don't know how to properly formulate the problem properly. Just to give another simple example in the absence of a better formulation: Say I have a square image (in TikZ) that I want to transform to a isosceles trapezoid image without any cropping occuring. – aahlback Sep 05 '23 at 12:08
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    @dexteritas Thanks! It would be nice to avoid using external TikZ-packages, but I suppose that tikz3d.dtx will solve the problem. I'll give it a try. – aahlback Sep 05 '23 at 12:15

1 Answers1

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Here's a way to draw and re-use isosceles trapezoids using \pic statements:

  • you define what to draw inside a \pic-style
  • you use \pic very similar to \node.

The solution comes in two parts:

    1. drawing a fixed trapezoid, to show basics
    1. allowing parameters passed to a \pic, a bit advanced

result

Part 1: fixed trapezoid

The basic idea is simple:

  • define 4 coordinates
  • draw a closed line (that's what cycle does)
  • call this pic-style e.g. trap

Call \pic as shown, and set some options.

\pic at (0,0) {trap};
Part 2: flexible trapezoid

What's new here is passing 3 arguments, where I decided to use / as delimiters. The overhead for this trap is a bit different, but you should spot the same coordinates and drawing as above. Also note the replacement by the arguments #1, #2 and #3. Specifying pic and arguments:

\pic at (0,0) {trap={2/4/1}};
Code:
\documentclass[10pt,border=3mm,tikz]{standalone}

\begin{document}
 \begin{tikzpicture}[
    trap/.pic={
        \coordinate (A) at ( 3,0);
        \coordinate (B) at (-3,0);
        \coordinate (C) at (-2,1);
        \coordinate (D) at ( 2,1);
        %

        \draw (A) -- (B) -- (C) -- (D) -- cycle;
    }
 ]
 \pic at (0,0) {trap};
 \pic[scale=.5,rotate=30] at (0,-2) {trap};
 \end{tikzpicture}


\begin{tikzpicture}
  [
    pics/trap/.style args={#1/#2/#3}% bottom, top, height
    {
     code={
        \coordinate (A) at ( #1,0);
        \coordinate (B) at (-#1,0);
        \coordinate (C) at (-#2,#3);
        \coordinate (D) at ( #2,#3);
        %

        \draw (A) -- (B) -- (C) -- (D) -- cycle;
     }
    }
 ]
 \pic at (0,0) {trap={2/4/1}};
 \pic[scale=.5,rotate=-30] at (0,-2) {trap={3/1/2}};
 \end{tikzpicture}
\end{document}
MS-SPO
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