Tag Archive for 'PHP Composite Pattern'

The Composite Design Pattern in PHP: Part IV Composite Drawing

Published on October 13, 2013 by Bill Sanders in Composite and SVG. 0 Comments Tags: , , , .

killeAppA Composite Drawing Program

In the original Gang of Four Composite example, (pp. 163-173 of Design Patterns) they showed a drawing program. It was broken down into separate leaves for Line, Rectangle, and Text. I included those leaves and added a Circle leaf. On the first rendering, I used .svg files, but that turned out to be far more limited and awkward than I wanted. Since PHP is not known as a language for doing graphics like ActionScript and Python (or Java for that matter), I wanted to use it for a dynamic engine for taking advantage of the HTML5 svg tag. To my surprise (and delight) I found that everything worked quite well with all of the browsers. I still only used subset of the six basic shapes provided in the SVG 1.1 W3 release. Text is considered a separate object apart from the basic shapes of:

  • rectangle
  • circle
  • ellipse
  • line
  • polyline
  • polygon

Before going further, it will help to look at the code and the example of employing the Composite pattern with Scalable Vector Graphics(SVG). Also, your might want to look at Part I, Part II and Part III of the Composite Pattern series on this blog. Use the Play button to see the composite SVG creation and click the Download button to get a zip file with all the code for the application;
PlayDownload

SVG Leaves

This Composite example employs the structure and most of the code from the full pattern example from Part III of this series. The major changes are to the leaf elements and rendering in the Composite. However, not a lot has changed otherwise, and that is one of the essential features of design patterns: re-use. First, take a look at the rectangle leaf class:

?View Code PHP 
< ?php
//Rectangle.php
class Rectangle extends IComponent
{
    private $xpos;
    private $ypos;
    private $wide;
    private $high;
    private $fill;
    private $stroke;
    private $strWidth;
 
    public function __construct($rx,$ry,$rw,$rh,$f,$sc,$sw)
    {
        $this->xpos=$rx;
        $this->ypos=$ry;
        $this->wide=$rw;
        $this->high=$rh;
        $this->fill=$f;
        $this->stroke=$sc;
        $this->strWidth=$sw;   
    }
 
    /* None of this batch of methods are used by shape or rectangle leaf */
    /* However in order to correctly implement the interface */
    /* you need some kind of implementation */
    public function add(IComponent $comOn){}
    public function remove(IComponent $comGone){}
    public function getChild($int){}
    protected function getComposite() {}
 
    /* Draw Rectangle */
    public function draw()
    {  
        echo "";
    }
}
?>
rect>

It does not use most of the inherited abstract classes but implements them because the structure calls for it. The draw() method then sets up the SVG parameters for the rectangle shape. As you will see, the other leaf classes do the same thing in the continuing page:
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