21 Dec 2009

For a long time I couldn't figure out how to make decent thumbnails with ImageMagick. Specifically, I wanted to create uniform sized thumbnails from arbitrary images. Over the weekend I came across the ImageMagick Examples page, which shows exactly how to do this. Here's the command for a 150x150 thumbnail,

convert orig.jpg -thumbnail 150x150^ -gravity center \
        -extent 150x150 thumb.jpg

It cuts out the largest square possible from the center of the image and resizes that to 150x150. This capability has actually only been available for 2 years now! It wasn't there last time I needed it.

I can think of one way to improve it: instead of selecting the center, it selects the area with the highest information density. This could be measured by edge detection, corner detection, or some other statistical method. It would be selected by changing the gravity option to, say, "entropy".

I'm listing this here mostly for my own future reference. :-)

13 Dec 2009

Sources:

git clone http://git.nullprogram.com/GameOfLife.git

Compiled (2009-12-13): GoL.jar (6.7kb)

Since I recently got back into Java recently, I threw together this little Game of Life implementation in Java. It looks a lot like my maze generator/solver on the inside, reflecting the way I think about these things. Gavin wrote a competing version of the game in Processing which we were partially discussing the other night, so I made my own.

The individual cells are actually objects themselves, so you could inherit the abstract Cell class and drop in your own rules. I bet you could even write a Cell that does the iterated prisoner's dilemma cellular automata. The Cell objects are wired together into a sort of mesh network. Instead of growing it wraps around on the sides.

It takes up to four arguments right now, with three types of cells, basic, implementing the basic Conway's Game of Life, growth, which is a cell that matures over time, and random which mixes both types together (seen in the screenshot). The arguments work as follows,

java -jar GoL.jar [<cell type> [<width> <height> [<cell pixel width>]]]

I may look into extending this to do some things beyond simple cellular automata.

06 Dec 2009

Developing C in Emacs is a real joy, and it's mostly thanks to the compile command. Once you have your Makefile -- or SConstruct or whatever build system you like -- setup and you want to compile your latest changes, just run M-x compile, which will run your build system in a buffer. You can then step through the errors and warnings with C-x `, and Emacs will take you to them. It's a very nice way to write code.

I use the compile command so much that I bound it to C-x C-k (C-k tends to be part of compile key bindings),

(global-set-key "\C-x\C-k" 'compile)

Until recently, I didn't have as nice of a setup for Java. Since they generally force offensive IDEs onto me at work this wasn't something I needed yet anyway, but I get to choose my environment on a new project this time. If you're using Makefiles for some reason when building your Java project, it still works out fairly well because they're usually called recursively. It gets more complicated with Ant, where there is only one top-level build file. Emacs' compile command only runs the build command in the buffer's current directory.

I know three solutions to this problem. One is to provide the build file's absolute path when compile asks for the command with the -buildfile (-f) option. You only need to type it once per Emacs session, so that's not too bad.

ant -emacs -buildfile /path/to/build.xml

It's not well documented, but there is a -find option that can be given to Ant that will cause it to search for the build file itself. This is even nicer than the previous solution. Just remember to place it last, unless you give it the build filename too. For example, if you wanted to run the clean target,

ant -emacs clean -find

To keep the actual call as simple as possible, I wrote a wrapper for compile, and put a hook in java-mode to change the local binding. The wrapper, ant-compile, searches for the build file the same way -find would do.

(defun ant-compile ()
  "Traveling up the path, find build.xml file and run compile."
  (interactive)
  (with-temp-buffer
    (while (and (not (file-exists-p "build.xml"))
                (not (equal "/" default-directory)))
      (cd ".."))
    (call-interactively 'compile)))

So I can transparently keep using my muscle memory compile binding, I set up the key binding in a hook,

(add-hook 'java-mode-hook
          (lambda () (local-set-key "\C-x\C-k" 'ant-compile)))

Voila! Java works looks a little bit more like C.

05 Dec 2009

Yesterday was a slightly chilly day, in the mid 50s (Fahrenheit), so when my officemate said we were getting snow I thought she was kidding. Well, today we woke up to this winter wonderland,

My wife leapt for her camera and filmed that as soon as she realized what was going on. We had much more than that by late afternoon. According to the Baltimore Sun it has snowed on December 5th for six of the last eight years, and we don't get much snow around here. My only wish would be for this to have happened on a weekday. I work for a university, and educational organizations tend to fold and give snow days really easily. This would probably have given me a nice paid day off!