The sketch
program above is nearly the simplest one possible,
the equivalent of a “hello world”
program you might find at the start of a programming language text.
If it is saved in the file simple.sk, then the command
sketch simple.sk -o simple.texcreates a file simple.tex containing
PSTricks
commands to
draw these objects on paper. The contents of simple.tex
look like this.
\begin{pspicture}(-1,-1)(2,2) \pstVerb{1 setlinejoin} \psline(-1,-1)(.333,.333) \pspolygon[fillstyle=solid,fillcolor=white](0,0)(1,0)(0,1) \psline(.333,.333)(2,2) \end{pspicture}The hidden surface algorithm of
sketch
has split
the line into
two pieces and ordered the three resulting objects so that the correct
portion of the line is hidden.
If you've noticed that the projection we are using seems equivalent to erasing the z-coordinate of the three-dimensional input points, pat yourself on the back. You are correct. This is called a parallel projection. The z-coordinate axis is pointing straight out of the paper at us, while the x- and y-axes point to the right and up as usual.
The resulting picture file can be included in a LaTeX document with
\input{simple}. Alternately, adding the command line option
-T1
causes the pspicture
to be wrapped in a short
but complete document, ready to run though LaTeX.
In a finished, typeset document, the picture looks like this. (The
axes have been added in light gray.)
It is important to know that only the “outside”
of a polygon is
normally drawn. The outside is where the vertices given in the
polygon
command appear in counter-clockwise
order. Thus, if the command above had been
polygon(0,1,0)(1,0,0)(0,0,1)the polygon would not appear in the picture at all. It would have been culled from the scene. This culling behavior may seem strange, but stay tuned.