Drawing Graphs Using TikZ in Emacs Org

1 Drawing a TikZ picture in Emacs Org Mode

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32

\usetikzlibrary{intersections,arrows.meta}
\begin{tikzpicture}[thin]
\draw (-1.5,0) -- (1.5,0);
\draw (0,-1.5) -- (0,1.5);
\filldraw[fill = green!20, draw = green!50!black] (0,0) circle[radius = 1cm];
\draw[help lines,very thin,step=.5cm,color=gray] (-1.5,-1.5) grid (1.5,1.5);
\draw (0,0) rectangle (.5,.5);
\draw (0,0) rectangle (-0.5,-0.5);
% relative coordinate
\draw[blue, very thick] (30:1) ++ (0,-0.5) --(0,0);
% name a path without drawing it
\path[name path = upward line] (1,0) -- (1,1);
\path[name path = sloped line] (0,0) -- (30:1.5cm);
% use intersection of two path
\draw[name intersections={of = upward line and sloped line, by=x}]
     [very thick, orange] (1,0) -- (x);
% use arrow
\draw[<->>] (0,0) -- (145:1);
\draw[<-{Triangle[fill=red]}] (0,0) -- (30:1);
% use scope
\begin{scope}[very thick]
\draw (-0.4,0.4) -- (0.4,0.4);
\draw (-0.4,-0.4) -- (0.4,-0.4);
\end{scope}
% use foreach
\foreach \x in {-1cm,-0.5cm,1cm}
    \draw[red] (\x,-3pt) -- (\x,3pt);
\foreach \y in {-1cm,-0.5cm,1cm}
    \draw[red](-3pt,\y) -- (3pt,\y);
% using node
\draw (0,0)+(0.2,-0.2) node {\tiny $(0,0)$ };
\end{tikzpicture}

The generated figure is shown as:

1. In the minimum working example line 12 , a path is named without drawing it.
2. Line 16 gives an example of using library intersections. Note that you need to add the library using \usetikzlibrary{intersections} otherwise an error occurs during \LaTeX compiling.
3. Line 18 and 19 gives an example of using arrow. To make it work, \usetikzlibrary{arrows.meta} is needed. The library arrows.meta provides tons of types of arrows whick shock me when I see them the first time.
4. Line 21 to 24 gives an example of scope . In the environment, all the lines are drawn in the very thick style.
5. Line 26 to 29 gives an examplt of foreach . foreach is handy when you want to draw a list of objects. In the minimum working example , I draw a list of short red sticks along with the x-axis and y-axis.
6. Line 31 is an example of node. The keyword node is typically followed by some options between [] and then some text between {}. Every node has flexible anchor options to decide where the text should be placed.

2 Another Example

The code is shown as:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14

\usetikzlibrary{intersections,arrows.meta}
\begin{tikzpicture}[scale=3]
  \clip (-0.6,-0.2) rectangle (0.6,1.51);
  \draw[step = .5cm, help lines] (-1.4,-1.4) grid (1.4,1.4);
  \filldraw[fill=green!20,draw = green!50!black] (0,0) -- (3mm,0mm)
  arc [start angle = 0, end angle = 30,radius = 3mm] -- cycle;
  \draw[->] (-1.5,0) -- (1.5,0);
  \draw[->] (0,-1.5) -- (0,1.5);
  \draw (0,0) circle [radius=1cm];
  \foreach \x in {-1,-0.5,1}
  \draw(\x cm, 1pt) -- (\x cm, -1 pt) node [anchor = north] {$\x$};
  \foreach \y in {-1,-0.5,1}
  \draw(1pt,\y cm) -- (-1pt, \y cm) node[anchor = east] {$\y$};
\end{tikzpicture}

The generated figure is shown as:

3 Some Basic Rules in TikZ

1. The options appear in []. No matter it is an object or an operation, the contents in the following [] serve as options.

   Options [] can be at the very beginning of the environment tikzpicture following the operation, following the object.

2. \filldraw is a good command. It draws a closed loop and fill it with color or pattern. The colors for filling and drawing can be different.

3. Coordinates can be specified in x-y format, polar format.

   • The easiest way is (x,y) which means x cm in the x-axis and y cm in the y-axis;
   • (a:x) is the polar format which means x cm in direction a degree.

4. (<p> |- <q>) is another way to specify coordinates for example (30:1 |- 0,0) which means the interaction of a vertical line through (30:1) and a horizontal line through (0,0) .

5. Relative coordinates are possible with + and ++ in front of (x,y) and (a:x) . + is relative to the closest coordinate whereas ++ is relative to the very first coordinate of current path.

4 Some tips for in TikZ

1. To use intersections to specify a coordinate, you need to include the library, i.e. \usetikzlibrary{intersections} is a must.

1
2
3
4
5

int main()
{
  int i=0;
  printf();
}

<~/Dropbox/research_library/zcl.bib>