commit 1385628548c5c69d9a5ac36595779783b54b4b18
parent 7ef82dd2a5346b228aa04a98344109cc68882c73
Author: Eamon Caddigan <eamon.caddigan@gmail.com>
Date: Sun, 22 Oct 2023 05:53:18 -0700
Post about graph paper (and example PDF)
Diffstat:
2 files changed, 107 insertions(+), 0 deletions(-)
diff --git a/content/posts/postscript-graph-paper/grid.pdf b/content/posts/postscript-graph-paper/grid.pdf
Binary files differ.
diff --git a/content/posts/postscript-graph-paper/index.md b/content/posts/postscript-graph-paper/index.md
@@ -0,0 +1,107 @@
+---
+title: "PostScript Graph Paper"
+date: 2023-10-22T05:52:41-07:00
+draft: true
+categories:
+- Programming
+---
+
+I needed some graph paper, and for my needs it seemed easier and more
+economical to print some at home than buy a whole pad of it. I turned to the
+web and found plenty of sites offering PDF files with grids on them, but I
+didn't like what I found[^pdfs] and decided to make my own.
+
+[Here's a PDF for a US Letter page with a 5 mm × 5 mm grid](grid.pdf).
+
+Drawing a grid is not difficult to do with a computer. The SVG format is
+pretty straightforward, so I considered writing a simple program to create a
+grid in SVG, and then using a second program to print it. But then I
+remembered: PostScript is a bona fide programming language! I could
+conceivably write the code to generate a graph paper grid in a file which
+could be printed directly. So I spent an afternoon familiarizing myself with
+PostScript and did that.
+
+I learned that PostScript is a stack based ("concatenative") language, like
+Forth or [UXNTAL](https://wiki.xxiivv.com/site/uxntal.html). I was playing
+with the latter last fall[^uxntal], so I have some familiarity with the
+paradigm. Stack programming seems strange when you're used to other
+paradigms, but I find it's not too hard to shift into the right mindset to
+write code this way once I get started.
+
+The complete PostScript program, which produced the PDF linked above,
+follows:
+
+```PostScript
+%!PS
+% Adjust these to suit your needs, units specified in "points" (1/72 inch)
+/w 612 def /h 792 def % US Letter paper
+/sp 5 72 mul 25.4 div def % Grid spacing (5 mm here)
+/st 1 72 mul 300 div def % Stroke width (1 'dots' in a 300 dpi resolution)
+/co 0.6 def % Gray-level of the line (0 = black, 1 = white)
+
+% Remainder function (`mod` doesn't take floating point values)
+/r {dup 3 1 roll div dup floor sub mul} def
+% Return the starting offset that centers the grid
+/o {r 2 div} def
+
+% Page and line setup
+<< /PageSize [w h] >> setpagedevice
+co setgray
+st setlinewidth
+
+% Create vertical lines
+w sp o
+sp w
+{
+ dup
+ 0 moveto
+ h lineto
+} for
+
+% Create horizontal lines
+h sp o
+sp h
+{
+ dup
+ 0 exch moveto
+ w exch lineto
+} for
+
+% Draw
+stroke
+```
+
+This code is probably not idiomatic or efficient, and I welcome feedback on
+writing better PostScript. But it worked for me and shouldn't be too hard to
+adapt to other page or grid sizes. Some might want to add margins to the
+page, but I decided that I would rather let my printer print as much grid as
+it was able; I just made sure to disable "print scaling".
+
+## Programming with PostScript
+
+If you're interested in playing with PostScript programming,
+[Ghostscript](https://www.ghostscript.com/) (which I used to convert the
+PostScript file to PDF) has an interactive interpreter that allows you to
+manipulate and view the stack (just type `stack`), and draw on a page. I
+just [came
+across](https://social.tchncs.de/@daveliepmann/111274696437077402) this
+relevant [quote from Peter Norvig](http://www.norvig.com/21-days.html):
+
+> _Play_. Which way would you rather learn to play the piano: the normal,
+> interactive way, in which you hear each note as soon as you hit a key, or
+> "batch" mode, in which you only hear the notes after you finish a whole
+> song? Clearly, interactive mode makes learning easier for the piano, and
+> also for programming. Insist on a language with an interactive mode and
+> use it.
+
+If you're like me and tend to open a calculator whenever you're faced with
+trivial arithmetic, I invite you to launch `ghostscript` and perform your
+calculations on the stack.
+
+[^pdfs]: For starters, these sites all branded their downloads—which may be
+ their right, but I didn't want an advertisement on my paper.
+
+[^uxntal]: I started learning it for a project I ought to pick back up. I
+ followed [compudanzas' _introduction to uxn
+ programming_](https://compudanzas.net/introduction_to_uxn_programming_book.html)
+ and recommend it!
