Filling part of a circle with a gradient following the circle-curve

Question

I want to fill the lower part of the circle (225° - 315°) with a gradient that is oriented to the curve of the circle. The whole sides at 225° and 315° should be the beginning of the colors. Now it's oriented to the tips on both sides.

  \fill[lightgray] (0,0) -- (90:5) arc (90:225:5) -- cycle;
\fill[left color=lightgray, right color=white] (0,0) -- (225:5) arc (225:315:5) -- cycle;

My idea is, that the gradient should orientate on a path like the one below (roughly drawn over the image), but i really do not know how to make that happen. I would highly appreciate any tipps or links to information that would be usefull to me.

[I looked here, but it does not seem to fit my problem.]

Full code:

\documentclass[10pt]{article}
\usepackage{blindtext}
\usepackage{fancyhdr}
\usepackage{ragged2e}
\usepackage[utf8]{inputenc}
\usepackage[labelformat=empty]{caption}
\usepackage{tikz}
%\usepackage{wrapfig}
\usetikzlibrary{mindmap,shadows,trees,shapes,through, positioning, backgrounds, fadings}
\usepackage{geometry}
 \geometry{
 a4paper,
 total={170mm,257mm},
 left=15mm,
 top=20mm,
 right=15mm
 }
\pagestyle{fancy}
\fancyhf{}
\rhead{\includegraphics[height=1.5cm]{XXX}}
\lhead{XXX}
%\rfoot{Page \thepage}
\begin{document}
\hfill
\centering
{\huge\textbf{mentales Lexikon\}}
\bigskip
\textbf{Übung zur Elaboration/Speicherung von Wörtern}\\smallskip von XXX
\bigskip
\begin{figure}[h!]
\begin{tikzpicture}[framed, text centered]
\coordinate (1) at (0,0);
  \coordinate (2) at (0,5);
\fill[lightgray] (0,0) -- (90:5) arc (90:225:5) -- cycle;
\fill[left color=lightgray, right color=white] (0,0) -- (225:5) arc (225:315:5) -- cycle;
%fill=left!30!white
\draw[black] (0:5)  -- (1);
  \draw[black] (45:5) -- (1);
  \draw[white] (90:5) -- (1);
  \draw[white] (135:5) -- (1);
  \draw[white] (180:5) -- (1);
  \draw[white] (225:5) -- (1);
  \draw[white] (270:5) -- (1);
  \draw[black] (315:5) -- (1);
\node [draw, circle through=(2), very thick] at (1) {};
\node [align=center] (episodisch) at (22.5:3.3) {episodische\Informationen};
  \node [align=center,draw, fill=white] (epi_note) at (22.5:6.7) {Quadratisch. Praktisch. Gut.\footnotemark\Informationen\???};
\node [align=center] (prozedual) at (67.5:3.3) {prozeduale\Informationen};
  \node [align=center,draw, fill=white] (proz_note) at (67.5:6.7) {Informationen \zur Handlung};
\node [align=center] (graphemisch) at (112.5:3.3) {graphemische\Informationen};
  \node [align=center,draw, fill=white] (graph_note) at (112.5:6.7) {Informationen \zur Schreibweise};
\node [align=center] (morphologisch) at (157.5:3.3) {morphologische\Informationen};
  \node [align=center,draw, fill=white] (morph_note) at (157.5:6.7) {morphologische \Informationen};
\node [align=center] (phonologisch) at (202.5:3.3) {phonologische\Informationen};
  \node [align=center,draw, fill=white] (phon_note) at (202.5:6.7) {kwadratisch\ipa\lautschrift};
\node [align=center] (syntaktisch) at (270:3.3) {syntaktische\Informationen};
  \node [align=center,draw, fill=white] (syn_note) at (270:6.7) {vor dem Nomen\Informationen};
\node [align=center] (semantisch) at (337.5:3.3) {semantische\Informationen};
  \node [align=center,draw, fill=white] (sem_note) at (337.5:6.7) {viereckig\mit gleich langen Seiten\Mathematik: in der zweiten Potenz\footnotemark};
\node [align=center, draw] (lemma) at (0:7.5) {\textbf{Lemma}};
  \node [align=center, draw, fill=lightgray] (lexem) at (180:7.5) {\textbf{Lexem}};
\node [rectangle, fill=white,draw] (quadratisch) at (0,0) {"quadratisch"};
\end{tikzpicture} 
\caption[test]{Modell eines Lexikoneintrages zum Wort "quadratisch"\footnotemark}
\end{figure}
\bigskip
\justifying
\blindtext[1]
\footnotetext[1]{\raggedright Werbeslogan der Schokoladenmarke Ritter Sport der Alfred Ritter GmbH &amp; Co. KG}
\footnotetext[2]{\raggedright Artikel des Wörterbuchs der deutschen Gegenwartssprache, elektronische Version, (1974) abgerufen unter https://www.dwds.de/wb/quadratisch}
\footnotetext[3]{\raggedright Modell nach Luger (2006) zitiert aus Reber K &amp; Schönauer-Schneider, W.(2018). Bausteine sprachheilpädagogischen Unterrichts. München: Reinhardt Verlag}
\end{document}

@Mensch Thanks! According to your username you speak my language. ;) — choXer, Nov 12 '21 at 20:35
Maybe this could help you getting started: https://tex.stackexchange.com/q/185728/47927 TikZ has only a ”color wheel” as polar gradient (which would be what you need), but you may be able to change the colors for this gradient. — Jasper Habicht, Nov 12 '21 at 21:46
Probably easier: use this approach and draw a very thick arc that covers the segment exactly. — Jasper Habicht, Nov 12 '21 at 22:14
Last idea: fill the segment white, draw a thick arc over it that fully covers it and use this approach to apply a gradient from gray to transparent to this path. Would this work? — Jasper Habicht, Nov 13 '21 at 08:57

polyn · Accepted Answer · 2021-11-13T23:59:28.497

\documentclass{article}
\usepackage{xfp}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\foreach \x in {0,...,100}
    \fill[white!\x!lightgray]
        (0,0) -- (\fpeval{\x=0 ? 225 : 225+\x*90/101-0.02}:5)
        arc[start angle=\fpeval{\x=0 ? 225 : 225+\x*90/101-0.02},
        end angle=225+\x*90/101+90/101,
        radius=5] -- cycle;
\end{tikzpicture}
\end{document}

without any package (except of course tikz)

\documentclass{article}
\usepackage{tikz}
\begin{document}
    \begin{tikzpicture}
        \foreach \x in {0,...,100}
        \fill[white!\x!lightgray]
        (0,0) -- (\ifnum \x=0 225 \else 225+\x*90/101-0.02 \fi:5)
        arc[start angle={\ifnum \x=0 225 \else 225+\x*90/101-0.02 \fi},
        end angle=225+\x*90/101+90/101,
        radius=5] -- cycle;
    \end{tikzpicture}
\end{document}

Wouldn’t this even be possible without any additional packages? It essentially draws a lot of tiny segments coloured in different shades of gray, right? +1 anyways — Jasper Habicht, Nov 13 '21 at 21:38

score 3 · Answer 2 · answered Nov 13 '21 at 13:30

Best I could come up with:

\documentclass[10pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{blindtext}
\usepackage{fancyhdr}
\usepackage{ragged2e}
\usepackage[labelformat=empty]{caption}
\usepackage{tikz}
%\usepackage{wrapfig}
\usetikzlibrary{mindmap, shadows, trees, shapes, through, positioning, backgrounds, fadings}
\usepackage{geometry}
 \geometry{
 a4paper,
 total={170mm,257mm},
 left=15mm,
 top=20mm,
 right=15mm
 }
\pagestyle{fancy}
\fancyhf{}
\rhead{\includegraphics[height=1.5cm]{example-image-a}}
\lhead{XXX}
% \rfoot{Page \thepage}
\begin{document}
\hfill
\centering
{\huge\textbf{mentales Lexikon\}}
\bigskip
\textbf{Übung zur Elaboration/Speicherung von Wörtern}\\smallskip von XXX
\bigskip
\begin{figure}[h!]
\begin{tikzpicture}[framed, text centered]
\coordinate (1) at (0,0);
  \coordinate (2) at (0,5);
\fill[lightgray] (0,0) -- (90:5) arc (90:225:5) -- cycle;
%\fill[left color=lightgray, right color=white] (0,0) -- (225:5) arc (225:315:5) -- cycle;
%%% polar gradient fill %%%
  \begin{scope}
    \clip (315:0) -- (315:5) arc (315:225:5) -- cycle;
    \foreach \i in {1,...,100} {
      \draw[white!\i!lightgray, line width=4pt] 
        ({225+\i(315-225)/100}:0) -- ({225+\i(315-225)/100}:5);
    }
  \end{scope}
  %%% === %%%
%fill=left!30!white
\draw[black] (0:5)  -- (1);
  \draw[black] (45:5) -- (1);
  \draw[white] (90:5) -- (1);
  \draw[white] (135:5) -- (1);
  \draw[white] (180:5) -- (1);
  \draw[white] (225:5) -- (1);
  \draw[white] (270:5) -- (1);
  \draw[black] (315:5) -- (1);
\node [draw, circle through=(2), very thick] at (1) {};
\node [align=center] (episodisch) at (22.5:3.3) {episodische\Informationen};
  \node [align=center,draw, fill=white] (epi_note) at (22.5:6.7) {Quadratisch. Praktisch. Gut.\footnotemark\Informationen\???};
\node [align=center] (prozedual) at (67.5:3.3) {prozeduale\Informationen};
  \node [align=center,draw, fill=white] (proz_note) at (67.5:6.7) {Informationen \zur Handlung};
\node [align=center] (graphemisch) at (112.5:3.3) {graphemische\Informationen};
  \node [align=center,draw, fill=white] (graph_note) at (112.5:6.7) {Informationen \zur Schreibweise};
\node [align=center] (morphologisch) at (157.5:3.3) {morphologische\Informationen};
  \node [align=center,draw, fill=white] (morph_note) at (157.5:6.7) {morphologische \Informationen};
\node [align=center] (phonologisch) at (202.5:3.3) {phonologische\Informationen};
  \node [align=center,draw, fill=white] (phon_note) at (202.5:6.7) {kwadratisch\ipa\lautschrift};
\node [align=center] (syntaktisch) at (270:3.3) {syntaktische\Informationen};
  \node [align=center,draw, fill=white] (syn_note) at (270:6.7) {vor dem Nomen\Informationen};
\node [align=center] (semantisch) at (337.5:3.3) {semantische\Informationen};
  \node [align=center,draw, fill=white] (sem_note) at (337.5:6.7) {viereckig\mit gleich langen Seiten\Mathematik: in der zweiten Potenz\footnotemark};
\node [align=center, draw] (lemma) at (0:7.5) {\textbf{Lemma}};
  \node [align=center, draw, fill=lightgray] (lexem) at (180:7.5) {\textbf{Lexem}};
\node [rectangle, fill=white,draw] (quadratisch) at (0,0) {"quadratisch"};
\end{tikzpicture} 
\caption[test]{Modell eines Lexikoneintrages zum Wort "quadratisch"\footnotemark}
\end{figure}
\bigskip
\justifying
\blindtext[1]
\footnotetext[1]{\raggedright Werbeslogan der Schokoladenmarke Ritter Sport der Alfred Ritter GmbH &amp; Co. KG}
\footnotetext[2]{\raggedright Artikel des Wörterbuchs der deutschen Gegenwartssprache, elektronische Version, (1974) abgerufen unter https://www.dwds.de/wb/quadratisch}
\footnotetext[3]{\raggedright Modell nach Luger (2006) zitiert aus Reber K &amp; Schönauer-Schneider, W.(2018). Bausteine sprachheilpädagogischen Unterrichts. München: Reinhardt Verlag}
\end{document}

The code essentially draw a lot of lines whose color shifts gradually from white to gray and whose angle gradually grows.

Shortcoming: the last line covers the other lines, which is quite visible.

Filling part of a circle with a gradient following the circle-curve

2 Answers2