To start, the createSilverlight.js file needs a bit of code. While colors can be passed as common names, I prefer working with hex values, which takes a little more work. As you saw earlier, the Fill.Color value returns a long. To convert that value to hex, add the following function (credit goes to Suyog Kale for posting this routine):

function getFillColor(color)
{
	var fill = color;
	if (fill < 0) {
		fill = (16777216 + parseInt(fill));
	}
	fill = fill.toString(16);
	if (fill.length > 6) {
		fill = fill.substr(fill.length - 6);
	}
	while (fill.length < 6) {
		fill = "0" + fill;
	}
	fill = "ff" + fill;
	return fill;
}

Note the last addition to the string: "ff". Silverlight works with 8-digit hex values for color, comprised of the 6-digit value preceded by "ff".

Replace the dropDots() function entirely with the following:

var dotColors="";

function dropDots(sender, mouseEventArgs)
{
	if (dotColors != "")
	{
		dotColors += ",";
	}
	dotColors += getFillColor(sender.Fill.Color);
	createDisplayCanvas();
}

Note the new global var "dotColors".

In the createDisplayCanvas() function, replace

source: "drawDots.php",

source: "drawDots.php?colors=" + dotColors, 

At this point, createSilverlight.js should look something like Listing 5.

Listing 5: Completed createSilverlight.js

function createControlPanel()
{
	Silverlight.createObjectEx({
		source: "controlPanel.xaml",
		parentElement: document.getElementById("dotControlPanel"),
		id: "slControlPanel",
		properties: {
			width: "100%",
			height: "100%",
			inplaceInstallPrompt:true,
			version: "1.0"
		}
	});
}


if (!window.Silverlight) 
	window.Silverlight = {};

Silverlight.createDelegate = function(instance, method) {
	return function() {
		return method.apply(instance, arguments);
	}
}

var dotColors="";

function dropDots(sender, mouseEventArgs)
{
	if (dotColors != "")
	{
		dotColors += ",";
	}
	dotColors += getFillColor(sender.Fill.Color);
	createDisplayCanvas();
}

function createDisplayCanvas()
{
    Silverlight.createObjectEx({
	source: "drawDots.php?colors=" + dotColors,
	parentElement: document.getElementById("dotDisplayCanvas"),
	id: "slDisplayCanvas",
		properties: {
			width: "100%",
			height: "100%",
			inplaceInstallPrompt:true,
			version: "1.0"
		}
	});
}

function getFillColor(color)
{
	var fill = color;
	if (fill < 0) {
		fill = (16777216 + parseInt(fill));
	}
	fill = fill.toString(16);
	if (fill.length > 6) {
		fill = fill.substr(fill.length - 6);
	}
	while (fill.length < 6) {
		fill = "0" + fill;
	}
	fill = "ff" + fill;
	return fill;
}

Replace the contents of drawDots.php entirely with Listing 6.

Listing 6: Completed drawDots.php

<?
header('Content-type: text/xml');
?>

<?
	$arrColors = explode(",",$_GET["colors"]);
	srand(time());
?>

<Canvas xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" x:Name="resultCanvas">

	<Canvas x:Name="Layer_1" Width="640" Height="80" Canvas.Left="0"

 Canvas.Top="0">

<?
	$n = 0;
	foreach ($arrColors as $c) {
		$n++;
		$lft = (rand()%530);
		$top = (rand()%370);
		echo('<Ellipse x:Name="Ellipse_' . $n . '" Width="100" Height="100" 

Canvas.Left="' . $lft . '" Canvas.Top="' . $top . '" Stretch="Fill" Fill="#' . $c . '"/>');
	}
?>

	</Canvas>
</Canvas>

As you can see, mouse events in the XAML file trigger a JavaScript routine which concatenates a global variable with the fill color of the selected dot. It then redraws the canvas by calling the createDisplayCanvas() function, which passes this string via GET to the PHP page.

The new PHP script explodes the GET string into an array, which can then be looped through via foreach. As an added bonus, I've added a bit of randomness to the equation by also setting Canvas.Left and Canvas.Top to random values within the Ellipse XAML echo. This serves no practical function whatsoever other than, hopefully, to stimulate the imagination a bit and induce more creative and interesting demonstrations of the technique.

The final result can be viewed here: www.justinwhitney.com/slphpdemo/PHPdemo.htm. You can also download a zip of the final source code here.

Where to Go From Here
This walkthrough barely scratches the surface of what you can do with Silverlight and PHP. Below are a few additional resources for investigating the topic further. If you come up with something cool, post it and send us a link.