It’s just a few lines of ghetto flavored javascript, but it does what it is supposed to. It works on Chrome/Chromium, Firefox and Opera. I don’t know (don’t care) if it will work on other browsers.
Download it here.

In case you want to further improve it, feel free to fork it on github:
https://gist.github.com/1748810.

This lame colorscheme generator was the result.

See it in action here
http://plainas.github.com/cubecolors ]]> http://lamehacks.net/blog/more-processing-js-fun/feed/ 0 http://lamehacks.net/blog/building-my-own-computer-from-scratch-kind-of/ http://lamehacks.net/blog/building-my-own-computer-from-scratch-kind-of/#comments Wed, 04 Jan 2012 04:00:42 +0000 admin http://lamehacks.net/blog/?p=274 I am reading The Elements of Computing Systems. I’ve been wanting to read a few computer science classics but I thought I would start by reading this instead (it’s not a classic… yet) as I feel like there are holes in my knowledge. Just as an example, I have never implemented a virtual machine nor have written an emulator. Those are the kind of basic challenges that every computer hacker should beat at least once.

This is a rather uncommon kind of textbook. First of all, it openly presents itself as a light accessible book that can easily be picked up by anybody with little knowledge of computing systems, but at the same time it sets a very ambitious goal to the reader: to build a computing system completely ‘from NAND to Tetris’. Secondly, there are no exercises for the reader to practice, there are project specifications that should be implemented by the reader. The projects are self contained, I could implement them in whichever order I wanted. That said, they communicative with each other through well defined interfaces so that in the end, the group of all the projects form a complete computing system.

I’ve red the first three chapters and it has been a joy to read and to implement the projects.

For more information about the book check out its official website.

But what’s a sate machine anyway?

From wikipedia:
A finite-state machine (FSM) or finite-state automaton (plural: automata), or simply a state machine, is a mathematical model used to design computer programs and digital logic circuits. It is conceived as an abstract machine that can be in one of a finite number of states. The machine is in only one state at a time; the state it is in at any given time is called the current state. It can change from one state to another when initiated by a triggering event or condition, this is called a transition. A particular FSM is defined by a list of the possible states it can transition to from each state, and the triggering condition for each transition.

To show how harmless state machines are, I’m going to model myself with a state machine. More specifically I’ll use a state machine to model a day at work.

So, my average work day consists of writting software in front of a computer screen. When I get bored I make a pause for coffee, after a few minutes I go back to work. If somebody calls for a meeting I imediatly follow, regardless if I’m working or having a coffee. Once the meeting is over I go back to work.

Let’s put this into a diagram for clarity.

If you’re an electrical enginner like myself, you’ll notice the similarity between this diagram and a state diagram of a circuit with flip-flops. That is not a coincidence, sequential logic circuits are state machines.

On to the implementation, I’ll use javascript, but obviously this can be done in your favorite language. But first, let’s start by specifying the sate machine by writting down all the states and transitions among them.

states = [
	{
		'name':'working',
		'initial':true,
		'events':{
			'bored':'coffee',
			'call_for_meeting':'meeting',
		}
	},
	{
		'name':'coffee',
		'events':{
			'break_over':'working',
			'call_for_meeting':'meeting'
		}
	},
	{
		'name':'meeting',
		'events':{
			'meetings_over':'working'
		}
	},
];

This is pretty self-explanatory.
The implementation is straightforward too: a constructor sets up the state machine when provided with a state machine definition such as the example above. Aditionally we define two extra methods, one to handle events and other to report the current state. What could be simpler?

function StateMachine(states){
	this.states = states;
	this.indexes = {}; //just for convinience
	for( var i = 0; i< this.states.length; i++){
		this.indexes[this.states[i].name] = i;
		if (this.states[i].initial){
			this.currentState = this.states[i];
		}
	}
	this.consumeEvent = function(e){
		if(this.currentState.events[e]){
			this.currentState = this.states[this.indexes[this.currentState.events[e]]] ;
		}
	}
	this.getStatus = function(){
		return this.currentState.name;
	}
}

And that’s it! Let’s see it in action.

sm = new StateMachine(states);
sm.getStatus(); // will return 'working'
 
sm.consumeEvent('bored');
sm.getStatus(); // I went for coffee
 
sm.consumeEvent('call_for_meeting');
sm.getStatus(); //will return 'meeting'
 
sm.consumeEvent('bored'); //doesn't matter how boring a meeting can be...
sm.getStatus(); //will still return 'meeting'
 
sm.consumeEvent('meetings_over')
sm.getStatus(); // 'working'

In many scenarios you might want to add some extra features such as signaling, external persistence or hooks, but this is basically it.

Most of the people that owned this camera most likely already replaced it. But for those who still have the camera laying on the back of some drawer, the fix is surprisingly quick and simple. And it will bring back this perfectly usable camera to life.

All you have to do is force the metal contact on the strip slightly out of its place. This way the metal contact between the metal and piece and the battery will be more effective.

With a pointy object such as a knife or a screw driver, press the tip of the metal lid so it bends until it gets out of it place. The picture bellow should give you a clearer idea:

Notice that you need to press from the tip of the strip first.

And here’s how it should look after the procedure

The lid will be slightly more difficult to close, but that’s barely noticeable.

I’ve seen dozens of fix suggestions that mention buying fancy batteries or install a custom firmware called CHDK which allows you to set the the threshold voltage that triggers the battery warning. All these sound like non-fixes to me, ultimately this is not a small software or electronics issue. It’s simply a malfunction electric contact. No camera setting or expensive batteries will fix that.

Download source.

Here’s the infamous system of linear equations solve example:

Let’s consider the following system of linear equations:

x + y + z = 1
x + 2y + 3z = 4
x + 4y + 8z = 8

from your first algebra class..

A.x = b
x = Inv(A).b

So let’s just to that

A = [[1,1,1],[1,2,3],[1,4,8]];
b = [[1],[4],[8]];
Ai = inverseMatrix(a);
x = matrixMultiply(Ai,b); //will return the solution [[28],[49],[22]] yay!!!

More examples and download at github.

Mmm…. turns out my rant is all but original.

So I ended up rolling my own. I googled around and picked galleria out of many javascript slideshow scripts, and wrapped it in a wordpress plugin.

Grab it from github.

Demo slideshow:

Here goes the current list of keyboard shortcuts:

Super+2		Place two windows side by side
Super+3		Place a window on the left half of the screen and two on the right half
Super+4		Arrange four windows two by two
Super+R		Rotate windows' positions i.e. cycle windows
Super+H		Resize and move current window to the left
Super+K		Resize and move current window to the right
Super+Y		Resize and move current window to left upper corner
Super+U		Resize and move current window to right upper corner
Super+B		Resize and move current window to left lower corner
Super+N		Resize and move current window to right lower corner

Download deb package.

Mapping url patterns into functions or Object methods is simple and easy. I’ll comment as I go…

//defining what url patterns get mapped into what funcitons.
//if no route is provided 'default' route is used
$routes = array(
	"default" => "sayhello",
	"hello" => "sayhello",
	"sum"  => "computesum"
);
 
/**
*Dispatch function - delegates action to other function and passes parameters to it
*/
function dispatch(){
 
	global $routes;
 
	//stear clear, allow only leters, numbers and slashes
	if(!empty($raw_route) and preg_match('/^[\p{L}\/\d]++$/uD', $_SERVER["PATH_INFO"]) == 0){
		die("Invalid URL");
	}
 
	//extract parameters
	$url_pieces = explode("/",$_SERVER["PATH_INFO"]);
	$action = $url_pieces[1];
	$params = array();
	if(count($url_pieces)>2){
		$params = array_slice($url_pieces, 2);
	}	
 
	//when no action is passed default action is performed
	if(empty($action)){
		$action="default";
	}
 
	//make sure the route is defined
	if(!in_array( $action, array_keys($routes))){
		die("Nothing to see here");
	}
 
	//all checked, execute requested funcion with provided parameters
	$action_function = $routes[$action];
	$action_function($params);
 
}
 
//just an example
function sayhello(){
	echo "Hello to you too!";
}
 
//another example
function computesum(){
	$params = func_get_arg(0);
 
	$sum = 0;
	$i=0;
	foreach($params as $par){
		$par = intval($par);
		$sum += $par;
		if ($i !=0){echo " + ".$par;}
		else{echo $par;}
		$i++;
	}
 
	echo " = " . $sum;
}
 
//run the whole thing
dispatch();

paste this into a file, for example dispatcher.php, put it on your server then try out urls like:

http://example.com/dispatcher.php/sum/1/2/3/4/10

http://example.com/dispatcher.php/hello

http://example.com/dispatcher.php

The file name can be removed if your server has support for url rewriting.