Graphics, Figures & Tables ⇒ Shading a circle

[coachbennett1981]

I am trying to shade the outside circle red and leave the "unit circle" alone. The circle has center )=O(0,0), but it is erased because I filled it white. Is there a better way to shade so I don't lose the center of the circle.

Code: Select all

	\begin{tikzpicture}[scale=2]
		\coordinate [label=left:$O$] (O) at (0,0);
		\coordinate [label=right:$$] (A) at (1,0);
		\coordinate [label=right:$$] (B) at (2,0);
		\node[draw,circle through=(A)] at (O){};
		\node[draw,circle through=(B)] at (O){};
		\filldraw[black](A) circle (1pt);
		\filldraw[black](B) circle (1pt);
		\filldraw[black](O) circle (1pt);
	\draw[fill,color=red](0,0) circle (2cm and 2cm);
	\draw[fill,color=white](0,0) circle (1cm and 1cm);
	\draw (O)--(A)--(B);
	\end{tikzpicture}

Nick

[shadgrind]

Try this:

Code: Select all

\begin{tikzpicture}[scale=2]
\coordinate [label=left:$O$] (O) at (0,0);
\coordinate [label=above left:$A$] (A) at (1,0);
\coordinate [label=right:$B$] (B) at (2,0);
\filldraw[fill=red] (B) arc (0:360:2) (A) arc (360:0:1);
\filldraw[black](A) circle (1pt);
\filldraw[black](B) circle (1pt);
\filldraw[black](O) circle (1pt);
\draw (O)--(A)--(B);
\end{tikzpicture}

[torbjorn t.]

Remember that the elements of the drawing are drawn in the order they appear in the code, so when the line of coding that fills the circles are drawn last, they will cover the parts that have been drawn before. By simply moving them to the top of the code, you get that you want:

Code: Select all

\begin{tikzpicture}[scale=2]
  \draw[fill,color=red](0,0) circle (2cm);
  \draw[fill,color=white](0,0) circle (1cm);
  \coordinate [label=left:$O$] (O) at (0,0);
  \coordinate [label=above right:$A$] (A) at (1,0);
  \coordinate [label=right:$B$] (B) at (2,0);
  \node[draw,circle through=(A)] at (O){};
  \node[draw,circle through=(B)] at (O){};
  \filldraw[black](A) circle (1pt);
  \filldraw[black](B) circle (1pt);
  \filldraw[black](O) circle (1pt);
  \draw (O)--(A)--(B);
\end{tikzpicture}

Note that you do not have to specify the radius two times when drawing circles. You only have to do that if you want an ellipse.


Another way is to use the pgfonlayer-environment (see section 65 in pgfmanual):

Code: Select all

\begin{tikzpicture}[scale=2]
  \coordinate [label=left:$O$] (O) at (0,0);
  \coordinate [label=above right:$A$] (A) at (1,0);
  \coordinate [label=right:$B$] (B) at (2,0);
  \node[draw,circle through=(A)] at (O){};
  \node[draw,circle through=(B)] at (O){};
  \filldraw[black](A) circle (1pt);
  \filldraw[black](B) circle (1pt);
  \filldraw[black](O) circle (1pt);
  \draw (O)--(A)--(B);
  \begin{pgfonlayer}{background}
    \draw[fill,color=red](0,0) circle (2cm);
    \draw[fill,color=white](0,0) circle (1cm);
  \end{pgfonlayer}
\end{tikzpicture}

[coachbennett1981]

Thank you so much!