This code was just scratch lying around, so it's not particularly well-documented. Sorry about that. Or well-refactored. Sorry about that too. You'll need RMagick to make it work. REALLY sorry about that. Don't forget to compile in .png support.
It was mostly an experiment in ruby fiddling, so the code is not fast by any means. It takes several hours to do a good 1080p render. This could be accomplished in a few seconds in C, but that wasn't the point when I wrote this. The point was to do it in Ruby, and that has been achieved. :-)
Good luck.
I think all you really need is imagemagick and libmagickwand-dev, but I installed libmagick-dev as well, not sure if it's needed.
# minimal install -- you may also need libmagick-dev
sudo apt-get install imagemagick libmagickwand-dev
gem install rmagick
Just run
ruby genimage.rb
Okay, this code was a brutal hack and I didn't really care about cleaning it up once it was done. I wanted Mandelbrot images, not the code to generate it. :-)
So... I noodled around inside the Mandelbrot function space, and found an area that I think looks quite attractive spread across two monitors, each 1920x1080. genimage with no modifications will emit mandel_right.png, which is the right half of the part of the fractal that I really liked. On lines 29/30 if you change which half is defined it will move the viewport over and emit the left half of the image. Conveniently, since I was trying to emit 2 images for 2 monitors, if you change the half to LEFT_HALF, the image file emitted will be named mandel_left.png.
Oh yeah. So I originally intended this to generate fractal images for my desktop at work. I had two monitors, so I needed two images, ideally rendering adjacent areas of the mandelbrot plane.
Since RMagick requires imagemagick, you'll have the convert tool at
your command-line. You can stitch the two images together with
convert mandel_left.png mandel_right.png +append mandel_big.png
In the very hacky genimage.rb file, you can manipulate the image
output by changing the constants at the top of the file. Specifically,
manipulating min_x, min_y and max_x on line 32 will change where
in the fractal you zoom in and render. Try backing it out to
[-1.0, -1.0, 1.0] to see the entire fractal in one image. max_y is
calculated by scaling the output aspect ratio. That's probably a bug
if you don't want to be locked into a single aspect ratio.
The fractal is rendered in patches, which is why SIZE_X is 192*4
rather than 1920. This was an optimization to let me test render small
parts of the image without changing the tiny floats that control
the fractal-space viewport.
Is the generator. All the parameters are hard-coded, sorry. There are some trivial image manipulation functions in there, mostly to adjust the viewport by scootching around the mandelbrot plane looking for interesting sections, and also to colorize the output on an interesting scale.
I wrote this about a year ago, so your guess is as good as mine when it comes to digging around in there to figure out what does what. If you document or refactor anything, please send me a pull request and I'll merge it in.
This is just a scratch file where I tried to generate an ascii-art mandelbrot fractal that would fit in a single tweet. There are several versions in there, all under 140 characters, that I have commented on. Special thanks to @brahbur on Twitter for helping me find the shortest possible optimization (so far).
Here's what mandelbrot.rb will emit:
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