Posts with the “gd” tag

Sunday afternoon project: Conway's Game of Life in PHP

gameoflife-1 gameoflife-2

As a way of spending my bank holiday Sunday afternoon, I decided to embark on a small project; I didn't know what the project would be when I first began browsing through Wikipedia but eventually I ended up in About.com's C++ challenge section, one of which concerned John Horton Conway's "Game of Life": a rudimentary cellular automaton which, after its inception in 1970, had immeasurable impact on fields as diverse as philosophy and theology. After toying with some ideas, I decided to build a script which automatically creates animations of a number of generations of the game. From that seed the project grew into the first steps towards an avatar system, much like the automatically generated Gravatars that currently adorn so many Wordpress based blogs.

I wanted something that was deterministic and identifiable
The first step was getting the algorithm working, and as I had already decided to make it web-based, that meant a PHP implementation. Using only the Wikipedia page as reference, I threw together a very basic script that allowed me to enter in some settings (grid dimensions, seed and generation limit) and for it to spit out the states between the seed and the generation cut off. After some wrangling with minor bugs (spelling errors, incorrect typing etc.) an unoptimised first version of the algorithm was complete:

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Tidbits from gallery.chaostangent.com

These are some of the neater parts of gallery.chaostangent.com that don't warrant a full exploration on their own but serve the goal of making the application more streamlined. I've crafted these examples to be focused so they don't contain superfluous details like error checking, timestamp columns and the like.

Database

The gallery schema is as follows:

CREATE TABLE IF NOT EXISTS `galleries` (
  `id` int(10) unsigned NOT NULL auto_increment,
  `left` int(10) unsigned NOT NULL default '0',
  `right` int(10) unsigned NOT NULL default '0',
  `parent` int(10) unsigned NOT NULL default '0',
  `title` tinytext NOT NULL,
  `directory` tinytext NOT NULL,
  PRIMARY KEY  (`id`),
  KEY `parent` (`parent`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 ;

This covers both the Modified Preorder Tree Traversal (`left` and `right` columns) model as well as the more standard hierarchical model (`parent` column). I'm still undecided as to whether indexing the `left` and `right` columns provides any benefits. Most of the queries on the gallery table involve getting the direct children of a particular node; the breadcrumb trail at the top of the page however is built using the `left` and `right` columns:

SELECT * FROM `galleries` WHERE (`left` >= ?) AND (`right` <= ?) ORDER BY `left`

Doing a multi-column index in MySQL works from the left column onwards, so for the above query, indexing on `left` and `right` would be a benefit. However when inserting and deleting nodes, queries are done singularly e.g. one for `left` and one for `right` which having an index on one and not the other may turn out to be detrimental in terms of update times. I could always do two indexes:

ALTER TABLE `galleries` ADD INDEX ( `left` , `right` ) ;
ALTER TABLE `galleries` ADD INDEX ( `right` , `left` ) ;

This runs the risk though of having a table that's more index than data. I haven't done a full benchmark of the different queries for each scenario but I would imagine only for large trees would indexing provide any tangible benefit.

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Rebuilding gallery.chaostangent.com

gallery.chaostangent.com front page
gallery.chaostangent.com is an application for storing and organising images – ostensibly a very simple desire but one I found not catered for by existing web applications when it was first conceived in 2005. The concept was an application that was simple and easy to use while still allowing for a degree of organisation to ensure images weren’t stored in a single “pool”.

With a small, well-defined feature set it seemed like a good time to address some of the issues which had crept in

Background

When I first started developing the application, PHP 5 hadn’t been released for very long and was receiving a mixed reception. Regardless, I started developing using a custom built framework I had cobbled together from scratch – one that would eventually go on to be refined and used in some of my work projects. With the lack of other mature frameworks to compare with, it was rough round the edges and did little more than segment out code into the MVC pattern and even then it wasn’t an entirely clean encapsulation; it was however useful.

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