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 This is my humble blog. Welcome.
 
+- [On Opening Black Boxes or: How I Learned to Stop Worrying and Love G-Code](opening-black-boxes.html) (28 Nov 2019)
 - [Adieu, Quake!](adieu-quake.html) (27 Aug 2019)
 
 Contact: <me@fwei.tk>
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+# On Opening Black Boxes or: How I Learned to Stop Worrying and Love G-Code
+
+![Baby Yoda, engraved.](baby-yoda.png)
+
+**TL;DR** PhotoVCarve should not cost $149. I made [my own](https://github.com/built1n/rastercarve).
+
+Recently I've gotten my hands on a 3-axis [ShopBot milling
+machine](https://www.shopbottools.com/products/max). For the
+uninitiated, a CNC mill is essentially a robotic carving machine --
+think "*robot drill*": you put in a piece of wood/foam/aluminum,
+program the machine, and out comes a finished piece with the right
+patterns cut into it. I had the idea of
+[engraving](https://en.wikipedia.org/wiki/Engraving) a raster image
+using the machine, and there happens to be a nice piece of software
+out there that claims to do just that: Vectric's
+[PhotoVCarve](https://www.vectric.com/products/photovcarve).
+
+There's just one problem: PhotoVCarve costs $149. Now, I have no
+qualms paying for software when it makes sense to do so, but in this
+case, $149 is simply excessive -- especially for a hobbyist. And
+besides, just see for yourself in the video below: all PhotoVCarve
+does is take an image and draw a bunch of grooves over it -- *nothing
+that couldn't be done in a couple lines of Python,* I thought.
+
+[![PhotoVCarve - Engraving Photographs](http://img.youtube.com/vi/krFyBxYwWW8/0.jpg)](https://www.youtube.com/watch?v=krFyBxYwWW8)
+
+## G-Code
+
+The first step in the process was figuring out *how* to control a CNC
+machine. Some Googling told me that virtually all machines read
+"G-code", a sequence of alphanumeric instructions that command the
+movement of the tool in 3 dimensions. It looks something like this:
+
+```
+G00 X0 Y0 Z0.2
+G01 Z-0.2 F10
+G01 X1.0 Y0
+```
+
+These three commands tell the machine to:
+
+1. Go to (0, 0, 0.2), rapidly (`G00` is "rapid traverse").
+2. Go to (0, 0, -0.2), slowly (`G01` commands a slower move than `G00`).
+3. Go to (1, 0, 0), slowly.
+
+My program just had to output the right sequence of G-code commands,
+which I could then feed into the ShopBot control software. (This was
+far simpler than I had originally imagined.)
+
+At this point, one of my flow states kicked in. I sat down, and got to
+coding.
+
+## The Program
+
+The development process was surprisingly straightforward -- I put in
+perhaps a total of 4 hours from my initial proof-of-concept to the
+current viable prototype. There were no major hiccups this time
+around, and even though I'm still in the process of learning it,
+Python made things *so* much easier than C (or God forbid -- [ARM
+assembly](adieu-quake.html)).
+
+The heart of my program is a function,
+[`engraveLine`](http://fwei.tk/git/rastercarve/tree/src/rastercarve.py?id=c2de4a3258c3e37d4b49a41d786eef936262f137#n118),
+which outputs the G-code to engrave one "groove" across the image. It
+takes in a initial position vector on the border of the image, and a
+direction vector telling it which way to cut.
+
+After this was written, it was a simple exercise to write a driver
+function to call `engraveLine` with the right vectors in the right
+sequence -- and that was all it took! (I really wonder how Vectric
+manages to charge $149 for this...)
+
+I fired up the program on a test image and fed its output into
+ShopBot's excellent G-code previewer. Success (see above)! I added a
+couple of tweaks (getting the lines to cut at an angle was fun) and I
+christened the program
+[*RasterCarve*](https://github.com/built1n/rastercarve).
+
+## Conclusion
+
+This was a fun little project that falls into the theme of "gradually
+opening up black boxes." G-code, I learned, isn't nearly as hard as it
+might seem. It's all too easy to abstract away the details of a
+technical process, but sometimes the best way to really understand
+something is by opening up the hood and tinkering with it.