Andy Li's Blog

If you haven’t heard about Brainfuck yet, it is a famous esoteric programming language. If you want to know why it has such a name take a look at its hello-world program source code (from wikipedia):

+++ +++ +++ +           initialize counter (cell #0) to 10
[                       use loop to set the next four cells to 70/100/30/10
    > +++ +++ +             add  7 to cell #1
    > +++ +++ +++ +         add 10 to cell #2
    > +++                   add  3 to cell #3
    > +                     add  1 to cell #4
    <<< < -                 decrement counter (cell #0)
]
>++ .                   print 'H'
>+.                     print 'e'
+++ +++ +.              print 'l'
.                       print 'l'
+++ .                   print 'o'
>++ .                   print ' '
<<+ +++ +++ +++ +++ ++. print 'W'
>.                      print 'o'
+++ .                   print 'r'
--- --- .               print 'l'
--- --- --.             print 'd'
>+.                     print '!'
>.                      print '\n'

the above program can be written as:

++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>.

So now you should know how lovely the language is and why I need to write a interpreter in Flash: now you can manipulate a ByteArray with BrainFuck code!!! And ya, the name of my interpreter is even more friendly than the language’s name!

Here is the result demo (source code here), type in a program and its input then click run. The default program is to add up two single-digit integers. And the output is correct only if the sum is single-digit too. And again the code is from wikipedia. You may find other BrainFuck source code to test from Panu Kalliokoski’s Brainfuck Archive.

The interpreter is written by only looking at its command description. There are some bugs as I know. For example when inputting multiple lines, the output may have wrong formating. And it can not have dynamic input like having inputs in a infinite loop. Actually any infinite loop will freeze your browser.

I don’t think I will go to improve it anytime soon. So please, don’t use it in production (will anyone??).

While traveling with my gf in Europe, I’m planning to develop a better technique to use color marker in FLARtoolkit (which I’ve tried before).

For the first step of doing so is to find a algorithm of matching colors. Using blend mode “difference” on the image is not flexible and may not fit all situations. I decided to calculate the difference by comparing hue, saturation and brightness of the colors and then threshold the image.

This is very similar to (if not exactly) doing chroma key. Maybe there is some awesome beautiful chroma key algorithm but I can’t find a fast and flexible enough to do so. If you know one, please tell me.

One problem I faced is choosing between color space models. RGB surely wouldn’t be the choice since it do not give hue value directly. There are HSV and HSL I found to be quite suitable. The two models share the same algorithm to calculate hue but have different ones for saturation and brightness. After reading the algorithms, my decision is… try both.

Another problem is how to preform thresholding. First method is after calculating the pixel difference, add the difference in hue, saturation and brightness altogether with weightings and do a one-time threshold to the gray-scale image. Second method is calculate the difference and give threshold limits to the three channels (H,S,V or H,S,L), only the pixels pass all the three thresholds will be white. First method should be more easily to incorporate with other filters developed for AR (like the very hot adaptive thresholding), but the second method can be more precise.  Finally I tried both too…

Here is the result. While I have set some default values to the filters, be sure to play around with the values when you change the target color. There wouldn’t be a set of values that fits all methods and situations.

I’ll try integrate it with FLARtoolkit and release the source when it is ready, be sure to check back soon.

Update:
Source and new demo is here!

Impressed by the video here, I tried to simulate the atomic model of metal in Flash using Box2DFlash.

What is done in the program is just put a lot of spheres in the area randomly, and then let the physics engine to solve all the collisions. When all the atoms stop moving, a single still of the metal structure will be formed.

The atoms are only drawn on the screen when it is sleeping (ie. no movement). It can save some time from not rendering them in each frame.

caution: The browser will freeze for a few seconds after “start” is pressed. And it takes several minutes to an hour to finish (when sleep count == atom count).