Old Project – TexGame

I uploaded a project, TexGame, from when I was 17 & 18 years old to github, it’s at https://github.com/bjwbell/texgame.

The code is in Python and uses PyGame for the graphics and sound.

The purpose of the game is to get as high a score as possible. To achieve this lines are eaten away. There is an eater block that goes across the screen. The rate at which it eats blocks depends on how many spaces it encounters. The more open spaces it eats the slower it moves, which is bad.

Menu Screen:


Old Project – World Racer

I uploaded a project, World Racer, from my teenager years to github. I apologize for the terrible spelling in the code, back then I had no idea how to spell almost anything.

I’ve looked at the code and it’s not bad. I’m surprised by how good of a C++ & 3d graphics programmer I was for the very first project I ever did.

The code is on github at https://github.com/bjwbell/WorldRacer.

World-Racer Screenshot

Emacs Rust Debugging


Use rust-gdb to launch gdb with the Rust-specific pretty-printers enabled, PR#19954 – add rust-gdb for Rust pretty printers.

GDB Rust Breakpoints

In gdb use break FILENAME:LINE_NUM instead of rbreak FUNCTION_NAME.
Rust has lifetime parameters, which can cause the gdb error umatched quote.

Code: struct Foo<‘a> {num: i32} impl<‘a> Foo<‘a> { fn add_one(self) {} }
    (gdb) rbreak add_one
     unmatched quote

Emacs GUD

  1. To Launch: M-x gdb
  2. Instead of gdb enter rust-gdb, add -args to pass arguments to the proccess being debugged.
  3. Example: rust-gdb --i=mi --args PATH_TO_EXECUTABLE EXECUTABLE_ARGS

Emacs GUD – Keybindings

I never remember the Emacs GUD keybindings, instead my .emacs includes:

(global-set-key [f5] 'gud-cont)
(global-set-key [f7] 'gud-tbreak)
(global-set-key [S-f11] 'gud-finish)
(global-set-key [f9] 'gud-break)
(global-set-key [f10] 'gud-next)
(global-set-key [f11] 'gud-step)

Emacs Rust Development Setup

========BASIC SETUP===========

=======PROJECT SETUP==========
Read the Cargo guide.

=======GGTAGS SETUP==========

For cross referencing via ggtags:

  1. Download and install Gnu Global (the Gnu Global package available in Ubuntu 14.04 doesn’t allow adding new lang defs).
  2. Ensure that $HOME/.ctags includes the Rust lang definitions from ctags.rust.
  3. Set the env variable GTAGSCONF to $HOME/.globalrc
  4. Set the env variable GTAGSLABEL to ctags, e.g. export GTAGSLABLE=”ctags”
  5. Sometimes eshell in emacs doesn’t inherit the env variables, in which case run gtags . in a normal shell.
  6. To .emacs add
    (add-hook 'prog-mode-hook
          '(lambda ()
             (when (derived-mode-p 'rust-mode) 
    	 (ggtags-mode 1))))
  7. Copy to .globalrc
    # Configuration file for GNU GLOBAL source code tag system.
    # Basically, GLOBAL doesn't need this file ('gtags.conf'), because it has
    # default values in its self. If you have the file as '/etc/gtags.conf' or
    # "$HOME/.globalrc" in your system then GLOBAL overwrite the default values
    # with the values in the file.
    # The format is similar to termcap(5). You can specify a target with
    # GTAGSLABEL environment variable. Default target is 'default'.
    # Configuration for gtags(1)
    # See gtags(1).
    # Built-in parsers.
    # Plug-in parser to use Exuberant Ctags.
    exuberant-ctags|plugin-example|setting to use Exuberant Ctags plug-in parser:\

Usable keyboard shortcuts for navigation, with Rust code:

  • M-.       – ggtags-find-tag-dwim – Go to definition
  • C-c M-g – ggtags-grep              – Grep for references

Bind ggtags-grep to “M-]”, for finding references:

(add-hook 'prog-mode-hook
      '(lambda ()
         (when (derived-mode-p 'rust-mode)
           (define-key ggtags-mode-map (kbd "M-]") 'ggtags-grep)

Implementing the Closest Pair Algorithm in OpenCL and WebCL

I was looking for a fun geometry problem to solve and came across the closest pair of points problem.

The problem statement is:
Given a set of points, in 2D, compute the closest pair of points.

The brute force algorithm takes O(n^2) time. There’s a better solution described at the Wikipedia page Closest pair of points problem, which takes O(n \cdot \textrm{log}(n)) time.
As far as I know, there aren’t any posted solutions using OpenCL to compute the closest pair. So I’ve implemented one, it’s posted at closest-pair.

There are a few challenges in adapting the algorithm for OpenCL. Namely, we can’t use recursion so we must convert the recursive algorithm to a procedural one. In this case it’s not to complicated because the structure of the solution is easily converted from the top-down recursive algorithm to a bottom-up parallel algorithm. There are some tricky issues when the number of points are not a power of 2. I’ve commented the code for those cases.

The second challenge is using WebCL. WebCL has an additional restriction that you can’t pass structures between Javascript and OpenCL kernels. Because of this I had to use dumb arrays of simple uint’s instead of using arrays of uint2, uint3, and uint4. This made the code more verbose. To help reduce the verbosity I added macros in the OpenCL ckStrips kernel. The WebCL version is posted at

I hope the solution is useful to someone. Enjoy reading the code, it requires careful thought.
Check it out at closest-pair or view the WebCL one online at closest_pair_ocl.html.

Enabling WebCL Highlighting in Emacs

When editing WebCL OpenCL kernels in Emacs I like to have the OpenCL kernel code highlighted as C code. This is easy to achieve using the multi-mode.el package.

The steps on Ubuntu (or any other modern Linux with Emacs 24) are

  1. Enable the http://marmalade-repo.org/ elpa package archive by adding the below to your .emacs file and restarting Emacs
        (require 'package)
        (add-to-list 'package-archives 
        '("marmalade" .
  2. Install multi-web-mode by using “M-x package-list-packages” and scrolling down to “multi-web-mode”.
  3. Add the below to the bottom of your .emacs file and restart Emacs
        (require 'multi-web-mode)
        (setq mweb-default-major-mode 'html-mode)
        (setq mweb-tags '((php-mode "<\\?php\\|<\\? \\|")
                          (js-mode "]*>" "")
                          (css-mode "]*>" "")
    	              (c-mode "]* +type=\"text/x-opencl\"[^>]*>" "")))
        (setq mweb-filename-extensions '("php" "htm" "html" "ctp" "phtml" "php4" "php5"))
        (multi-web-global-mode 1)

    The important part is the “c-mode” section that will enable C highlighting for OpenCL kernels in html files.

  4. Start coding!