I became intrigued by the problem of finding the color at any point of a rectangle that has been filled with a LinearGradientBrush.  There is are techniques for doing this by essentially sampling the pixel at a rendered point but I wanted to approach the problem algorithmically.

I developed the following method which receives a rectangle object that has been filled with a LinearGradientBrush and a point relative to the upper left corner of the rectangle and returns the calculated color at that point.  There are no restrictions on the Start/Stop Points or the number of GradientStops.  The ColorInterpolationMode can be either SRgbLinearInterpolation (default) or ScRgbLinearInterpolation.  The GradientSpreadMethod is required to be the default (Pad).

There are two methods below:

Color GetColorAtPoint(Rectangle r, Point p) – finds the color at any point of a LinearGradientBrush filled rectangle.

private Double dist(Point px, Point po, Point pf) – helper method for GetColorAtPoint.

To use, copy both methods to your class and call GetColorAtPoint() with a rectangle and point.

//Calculates the color of a point in a rectangle that is filled

//with a LinearGradientBrush.

private Color GetColorAtPoint(Rectangle theRec, Point thePoint)

{

    //Get properties

    LinearGradientBrush br = (LinearGradientBrush)theRec.Fill;

    double y3 = thePoint.Y;

    double x3 = thePoint.X;

    double x1 = br.StartPoint.X * theRec.ActualWidth;

    double y1 = br.StartPoint.Y * theRec.ActualHeight;

    Point p1 = new Point(x1, y1); //Starting point

    double x2 = br.EndPoint.X * theRec.ActualWidth;

    double y2 = br.EndPoint.Y * theRec.ActualHeight;

    Point p2 = new Point(x2, y2);  //End point

    //Calculate intersecting points 

    Point p4 = new Point(); //with tangent

    if (y1 == y2) //Horizontal case

    {

        p4 = new Point(x3, y1);

    }

    else if (x1 == x2) //Vertical case

    {

        p4 = new Point(x1, y3);

    }

    else //Diagnonal case

    {

        double m = (y2 - y1) / (x2 - x1);

        double m2 = -1 / m;

        double b = y1 - m * x1;

        double c = y3 - m2 * x3;

        double x4 = (c - b) / (m - m2);

        double y4 = m * x4 + b;

        p4 = new Point(x4, y4);

    }

    //Calculate distances relative to the vector start

    double d4 = dist(p4, p1, p2);

    double d2 = dist(p2, p1, p2);

    double x = d4 / d2;

    //Clip the input if before or after the max/min offset values

    double max = br.GradientStops.Max(n => n.Offset);

    if (x > max)

    {

        x = max;

    }

    double min = br.GradientStops.Min(n => n.Offset);

    if (x < min)

    {

        x = min;

    }

    //Find gradient stops that surround the input value

    GradientStop gs0 = br.GradientStops.Where(n => n.Offset <= x).OrderBy(n => n.Offset).Last();

    GradientStop gs1 = br.GradientStops.Where(n => n.Offset >= x).OrderBy(n => n.Offset).First();

    float y = 0f;

    if (gs0.Offset != gs1.Offset)

    {

        y = (float)((x - gs0.Offset) / (gs1.Offset - gs0.Offset));

    }

    //Interpolate color channels

    Color cx = new Color();

    if (br.ColorInterpolationMode == ColorInterpolationMode.ScRgbLinearInterpolation)

    {

        float aVal = (gs1.Color.ScA - gs0.Color.ScA) * y + gs0.Color.ScA;

        float rVal = (gs1.Color.ScR - gs0.Color.ScR) * y + gs0.Color.ScR;

        float gVal = (gs1.Color.ScG - gs0.Color.ScG) * y + gs0.Color.ScG;

        float bVal = (gs1.Color.ScB - gs0.Color.ScB) * y + gs0.Color.ScB;

        cx = Color.FromScRgb(aVal, rVal, gVal, bVal);

    }

    else

    {

        byte aVal = (byte)((gs1.Color.A - gs0.Color.A) * y + gs0.Color.A);

        byte rVal = (byte)((gs1.Color.R - gs0.Color.R) * y + gs0.Color.R);

        byte gVal = (byte)((gs1.Color.G - gs0.Color.G) * y + gs0.Color.G);

        byte bVal = (byte)((gs1.Color.B - gs0.Color.B) * y + gs0.Color.B);

        cx = Color.FromArgb(aVal, rVal, gVal, bVal);

    }

    return cx;

}

//Helper method for GetColorAtPoint

//Returns the signed magnitude of a point on a vector with origin po and pointing to pf

private double dist(Point px, Point po, Point pf)

{

    double d = Math.Sqrt((px.Y - po.Y) * (px.Y - po.Y) + (px.X - po.X) * (px.X - po.X));

    if (((px.Y < po.Y) && (pf.Y > po.Y)) ||

        ((px.Y > po.Y) && (pf.Y < po.Y)) ||

        ((px.Y == po.Y) && (px.X < po.X) && (pf.X > po.X)) ||

        ((px.Y == po.Y) && (px.X > po.X) && (pf.X < po.X)))

    {

        d = -d;

    }

    return d;

}

The method works by projecting the input point onto the vector that is described by the LinearGradientBrush Start/Stop points.  There are special cases for horizontal and vertical lines.  The width of the line is calculated as well as the relative distance of the projected point from the StartPoint (using the dist() method).  The GradientStops are ordered and two stops are found that are the closest the projected point.  The color channel values are interpolated based on the relative position of the projected point and these two stops.  The values are assembled into a color and returned.

You can download a demo of this method here.

I highly recommend Kaxaml for your XAML editor.  Not only does it look and work great but it also has some very useful features not found on other XAML editors.

I won’t bother listing all of the features that you can read about here, but my favorites are Intellisense support (with code completion!), snippets including a generous collection of simple control styles and the ability to create and save your own, drag and drop, a beautiful color picker, and a XAML scrubber.

With other XAML editors, I thought, “what’s the point? Just use the designer in Visual Studio.”  But Kaxaml is one tool that I will use first to build and customize my UIs–largely due to its snippets, colorpicker and ease of use.  (I don’t use Blend.)

Download Kaxaml here: www.kaxaml.com

Silverlight has a MediaElement control  which can be used for most cross-platform media display tasks.  I was disappointed that my application can not use it because it currently does not support playback at a variable rate.

My application requires a media player that can playback speech mp3 files at rates varying from 0.5 to 1.0x realtime.  Windows Media Player (WMP) is especially good at this in that the playback at reduced speed does not modify the pitch of the speech.

My solution to this problem is to instantiate a WMP or Quicktime player in the page depending on the platform and control the player from Silverlight C# code through a Javascript layer.

First, the player is installed in the body of the html page like this:

<!--Player goes here-->
     <div id="PlayerDiv"></div>    

 <script type="text/javascript">  

 //Installs the player
 var wmp;
 var qtp;
 document.getElementById('PlayerDiv').innerHTML = playerCreate('news clip.mp3');
 if(useWmp){
 wmp = document.getElementById('wmPlayer');
 }else{
 qtp = document.qtPlayer;
 }    

 </script>

The playerCreate function is a bit of Javascript that determines the browser capabilities and installs either a WMP or Quicktime player.  If IE is detected or Firefox is detected with the WMP component, then WMP is installed else use Quicktime.  (WMP is preferred over Quicktime for this application because while Quicktime has a rate control, the pitch is not preserved for mp3 playback.)  Here is the playerCreate Javascript:

var useWmp;
    function playerCreate(url) {
    //Find browser
var userAgent = navigator.userAgent.toLowerCase();
var is_opera  = (userAgent.indexOf('opera') != -1);
var is_saf    = ((userAgent.indexOf('applewebkit') != -1) || (navigator.vendor == "Apple Computer, Inc."));
var is_webtv  = (userAgent.indexOf('webtv') != -1);
var is_ie     = ((userAgent.indexOf('msie') != -1) && (!is_opera) && (!is_saf) && (!is_webtv));
var is_ie4    = ((is_ie) && (userAgent.indexOf("msie 4.") != -1));
var is_moz    = ((navigator.product == 'Gecko') && (!is_saf));
var is_kon    = (userAgent.indexOf('konqueror') != -1);
var is_ns     = ((userAgent.indexOf('compatible') == -1) && (userAgent.indexOf('mozilla') != -1) && (!is_opera) && (!is_webtv) && (!is_saf));
var is_ns4    = ((is_ns) && (parseInt(navigator.appVersion) == 4));   

    var str = "";
    if (is_ie) {
    // create the WMP for IE 
    useWmp = true;
    str = '<object id="wmPlayer" classid="CLSID:6BF52A52-394A-11d3-B153-00C04F79FAA6" width="0" height="0">';
//    str += '<param name="URL" value="'+url+'" />'; 
    str += '<param name="uiMode" value="none">';
    str += '<param name="autoStart" value="false">';
    str += '</object>';
    return str;  

    }else if(is_moz && navigator.plugins["Microsoft® Windows Media Player Firefox Plugin"]){
    // create WMP for FF. 
    useWmp = true;
    str = '<object id="wmPlayer" type="application/x-ms-wmp" data="'+url+'" width="0" height="0">';
//    str += '<param name="URL" value="'+url+'" />'; 
    str += '<param name="uiMode" value="none">';
    str += '<param name="autoStart" value="false">';
    str += '</object>';
    return str;      

    }else{
    //try to create the qtp as last resort
    useWmp = false;
    str ='<object id="qtPlayer" classid="clsid:02BF25D5-8C17-4B23-BC80-D3488ABDDC6B" codebase="http://www.apple.com/qtactivex/qtplugin.cab"  width="0" height="0" >';
//    str += '<param name="src" value="'+url+'">';
    str += '<param name="autoplay" value="false">';
    str += '<embed  name="qtPlayer" width="0" height="0" src="qtStartUp.mp3" mce_src="qtStartUp.mp3" AUTOPLAY="false" TYPE="audio/mpeg" PLUGINSPAGE="www.apple.com/quicktime/download" enablejavascript="true">';
    str += '  </embed> ';
    str += '</object> ';
    return str;  

}
}

A set of Javascript functions were defined in order to create a common API for the Silverlight C# code to use.

function playerPlay(){
if(useWmp){
wmp.controls.play();
}else{
qtp.Play();
}
}  

function playerStop(){
if(useWmp){
wmp.controls.stop();
}else{
qtp.Stop();
qtp.Rewind();
}
}   

function playerPause(){
if(useWmp){
wmp.controls.pause();
}else{
qtp.Stop();
}
}   

function playerUrl(url){  

if(useWmp){  

wmp.URL = url;
}else{
qtp.SetURL(url);
qtp.Stop();
}
}   

function playerGetPosition(){
if(useWmp){
return wmp.controls.currentPosition;
}else{
return qtp.GetTime()/600;
}
}   

function playerSetPosition(t){
if(useWmp){
wmp.controls.currentPosition = t;
}else{
qtp.SetTime(t*600); //int
}
}   

function playerSetVolume(v){
if(useWmp){
wmp.settings.volume = v;
}else{
qtp.SetVolume(v); //int 0-100
}
}   

function playerSetRate(r){
if(useWmp){
wmp.settings.rate = r;
}else{
qtp.SetRate(r); //flost 0.5-1.0
}
}

These functions are called by a single event handler that manages calls from the Silverlight C# code using the techniques for C# to Javascript communications described in the QuickStart guide.

//Event handler for Silverlight control
function agEventHandler(sender, args){
switch (args.Name){
case 'stop':
playerStop();
break;
case 'play':
playerPlay();
break;
case 'pause':
playerPause();
break;
case 'url':
playerUrl(args.Sdata);
break;
case 'position':
playerSetPosition(args.Data);
break;
case 'volume':
playerSetVolume(args.Data);
break;
case 'rate':
playerSetRate(args.Data);
break;  

default:
}

The event handler arguments are defined on the C# side as follows:

//This class defines the arguments for the control's events
[Scriptable]
public class CustomEventArgs : EventArgs
{
    private double data;
    private string name;
    private string sdata;  

    public CustomEventArgs(string iname, double idata, string isdata)
    {
        data = idata;
        name = iname;
        sdata = isdata;
    }  

    [Scriptable]
    public string Name
    {
        get { return name; }
        set { name = value; }
    }  

    [Scriptable]
    public double Data
    {
        get { return data; }
        set { data = value; }
    }  

    [Scriptable]
    public string Sdata
    {
        get { return sdata; }
        set { sdata = value; }
    }
}//End of class

This class of custom event arguments allows the passing of a string name which specifies the media player event to control as well as a double and string parameter for data.

The event method is defined in the C# code like this:

//This defines the event from the control
//This is an example of how to fire an event from the control to Javascript
//AgEvents(this, new CustomEventArgs("hello", 25, "something"));
[Scriptable]
public event EventHandler<CustomEventArgs> AgEvents;

Finally, here is an example of C# code controlling the media player:

void play()
{
    if (playerState != (int)playerStates.paused)
    {
        AgEvents(this, new CustomEventArgs("position", t1, null));
    }  

    AgEvents(this, new CustomEventArgs("play", 0, null));

 You can see a demo of this application here.

 You can download the demo project here.

Hopefully, future releases of Silverlight will have a MediaElement with a rate control so that my application can be greatly simplified.

I needed a timer control for a Silverlight 1.1 application but it is not supported in the Alpha release.  My solution was to use the timer in Javascript and have it send events to the C# code.

Event sending from Javascript to C# is described in the Silverlight QuickStart document.

Here is the initialization of the timer in Javascript:

//initialize silverlight event hookup and start timer
var control;
function init(sender){
control = sender;
control.Content.basic.AgEvents = agEventHandler;
setInterval(jtimer,10);
}

In this routine, the timer is set to execute the jtimer function every 10 ms.  (The agEvents statement is used for sending information to the Javascript.  I will describe this later.)

The init function is called by the CreateSilverlight function in the page.js file:

// JScript source code 

//contains calls to silverlight.js, example below loads Page.xaml
function createSilverlight()
{
    Silverlight.createObjectEx({
        source: "Page.xaml",
        parentElement: document.getElementById("SilverlightControlHost"),
        id: "SilverlightControl",
        properties: {
            width: "100%",
            height: "100%",
            version: "1.1",
            enableHtmlAccess: "true",
            isWindowless: "True"
        },
        events: {
        onLoad: init
        }
    }); 

    // Give the keyboard focus to the Silverlight control by default
    document.body.onload = function() {
      var silverlightControl = document.getElementById('SilverlightControl');
      if (silverlightControl)
      silverlightControl.focus();
    }
}

Here is the jtimer function:

//Send position of player to silverlight based on a timer
function jtimer(){
control.Content.basic.timer(playerGetPosition());
}

In this function, a function timer is called in the C# code with a value that is passed as an argument.

On the C# side, the timer function looks like this:

        //This receives the timer event from Javascript
        [Scriptable]
        public void timer(double arg)
        {
            tnow = arg;

…

Note the ‘[Scriptable]‘ tag which makes the timer function usable from Javascript.

Finally, the page load event needs some boilerplate to hook the Javascript to C# communications:

        public void Page_Loaded(object o, EventArgs e)
        {
            // Required to initialize variables
            InitializeComponent();
            //Register the scriptable endpoints
            WebApplication.Current.RegisterScriptableObject("basic", this);