Drawing geometric shapes

We want to progress from high-speed to advanced TikZ concepts, so let’s have a compact summary of what we can draw in this basic setting – that is, we start with \draw <coordinate> (that’s the current coordinate) and continue with some of the following elements:

• Line: -- (x,y) draws a line from the current coordinate to (x,y).
• Rectangle: rectangle (x,y) draws a rectangle where one corner is the current coordinate, and the opposite corner is (x,y).
• Grid: Like rectangle but with lines in between as a grid.
• Circle: circle (r) was a short syntax we used previously, but the extended syntax is circle [radius=r], which draws a circle with the center at the current coordinate and a radius of r.
• Ellipse: ellipse [x radius = rx, y radius = ry] draws an ellipse with a horizontal radius of rx and a vertical radius of ry. The short form is ellipse (rx and ry).
• Arc: arc[start angle=a, end angle=b, radius=r] gives a part of a circle with a radius of r at the current coordinate, starting from angles a to angles b. The short command version is arc(a:b:r).

arc[start angle=a, end angle=b, x radius=rx, y radius=ry] gives a part of an ellipse with an x radius of rx and a y radius of ry at the current coordinate, starting from angle a and going to angle b. The short syntax would be arc(a:b:rx and ry).

Let’s have a few examples to see what these commands do:

1. Draw a circle with a radius of 2 at the origin:

   \draw (0,0) circle [radius=2];

2. Next, draw an ellipse with a horizontal radius of 0.2 and a vertical radius of 0.4:

   \draw (-0.5,0.5,0) ellipse [x radius=0.2, y radius=0.4];

3. Now, draw the same ellipse at (0.5,0.5):

   \draw (0.5,0.5) ellipse [x radius=0.2, y radius=0.4];

4. Next, draw an arc that looks like a smile:

   \draw (-1,-1) arc [start angle=185, end angle=355,

     x radius=1, y radius=0.5];

5. Finally, draw a rectangle with the lower-left corner at -3,-3 and the upper-right corner at 3,3:

   \draw (-3,-3) rectangle (3,3);

When you use all the commands from steps 1 to 5 in a tikzpicture environment and compile, you get the following:

Figure 2.9 – A smiley in a rectangle

This result of the command examples still looks a bit dull. Let’s improve it a bit and fill it with color.