WPF Custom Screen Saver Art

Erik Klimczak — Fri, 20 Jun 2008 15:24:00 GMT

Summary

Creating custom wallpaper is easy. But what about custom screen savers? This post will detail how to build a custom saver using Windows Presentation Framework (WPF). The posted code also provides some insight on how to create interesting particle effects using WPF's animation engine, and how to implement multiple monitor support in .Net.

Erik Klimczak - Clarity Consulting

Download

http://wpfscreensaverart.codeplex.com/

Introduction

Microsoft Unified Communications (UC) is a new technology that has been getting a lot of hype in the past couple of months. UC is essentially the integration of messaging, voice, and video across the applications and devices that people use every day. More information about UC can be found here. One of the coolest things about UC is the concept of “presence” (see below). The Presence indicator effectively allows the user to reflect his/her status in other Office Communicator Server friendly applications (i.e. Outlook, Office communicator, Live Meeting, etc.)

While building out some communicator functionality on another project I found myself recreating the presence “bubbles” in xaml so that they could scale without losing quality (see below). I used Expression Design to re-create the presence bubbles and export then to xaml.

In doing so it occurred to me that the presence “bubbles” would make for some excellent art sprites.

So after a hop-skip-and a jump to Photoshop I found myself with a shiny new “presence art” wallpaper.

Immediately after creating the wallpaper I thought to myself, “this would also make a great screen saver”. This article will attempt to show how to build a custom WPF screen saver that implements a simple physics particle effect using the WPF animation engine.

Particle Animation

With my graphic designer hat on I knew that I wanted to create a floating particle effect. Particle effects can be used to simulate anything from rain, snow, fire to bubbles and clouds. Then by varying the presence “bubbles” in size and opacity the illusion of depth and space can be created. After some research I found the CompositionTarget.Rendering event handler in WPF. Essentially, this event is a timer that ticks all the time and fires once each time WPF decides to render a frame. Inside the event handler you have complete freedom to do whatever you want to any object. In other words, hooking CompositionTarget.Rendering is very much a "do it yourself" animation system. This event is especially good for physics-based animations and is very similar to the way Flash's rendering engine works. The MSDN entry for this event handler can be found here.

Once I had found the appropriate animation hook I created the particle user control. This control holds the various particle attributes that will be animated. The code below shows the various properties that can be used to create very interesting physics-based effects. These properties can be used to calculate collision detection, gravitational pull and other kinetics-related effects.

   1: public partial class Particle : UserControl

   2:    {

3:

   4:        public Particle()

   5:        {

6:

   7:            InitializeComponent();

   8:        }

9:

  10:        public static readonly DependencyProperty StatusProperty = DependencyProperty.Register("Status", typeof(Status), typeof(Particle), new UIPropertyMetadata(Particle.StatusValueChanged));

  11:        public Status Status

  12:        {

  13:            get { return (Status)GetValue(StatusProperty); }

  14:            set { SetValue(StatusProperty, value); }

  15:        }

16:

  17:        private static void StatusValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)

  18:        {

  19:            Particle myclass = (Particle)d;

  20:            myclass.imgStatus.Source = Application.Current.FindResource(((Status)e.NewValue).ToString() + "Png") as BitmapImage;

  21:        }

22:

  23:        public double Radius

  24:        {

  25:            get { return this.imgStatus.Height / 2; }

  26:            set { this.imgStatus.Height = this.imgStatus.Width = value * 2; }

  27:        }

28:

  29:        private double vy;

  30:        public double VY

  31:        {

  32:            get { return this.vy; }

  33:            set { this.vy = value; }

  34:        }

35:

  36:        private double vx;

  37:        public double VX

  38:        {

  39:            get { return this.vx; }

  40:            set { this.vx = value; }

  41:        }

42:

  43:        private double mass;

  44:        public double Mass

  45:        {

  46:            get { return this.mass; }

  47:            set { this.mass = value; }

  48:        }

  49:        private double x;

  50:        public double X

  51:        {

  52:            get { return this.x; }

  53:            set { this.x = value; }

  54:        }

55:

  56:        private double y;

  57:        public double Y

  58:        {

  59:            get { return this.y; }

  60:            set { this.y = value; }

  61:        }

  62:    }

VB

   1: Partial Public Class Particle

   2:     Inherits UserControl

3:

4:

   5:     Public Sub New()

   6:         InitializeComponent()

   7:     End Sub

8:

   9:     Public Shared ReadOnly StatusProperty As DependencyProperty = DependencyProperty.Register("Status", GetType(Status), GetType(Particle), New PropertyMetadata(AddressOf Particle.StatusValueChanged))

  10:     Public Property Status() As Status

  11:         Get

  12:             Return CType(GetValue(StatusProperty), Status)

  13:         End Get

  14:         Set(ByVal value As Status)

  15:             SetValue(StatusProperty, value)

  16:         End Set

  17:     End Property

18:

  19:     Private Shared Sub StatusValueChanged(ByVal d As DependencyObject, ByVal e As DependencyPropertyChangedEventArgs)

  20:         Dim [myclass] As Particle = CType(d, Particle)

  21:         [myclass].imgStatus.Source = TryCast(Application.Current.FindResource((CType(e.NewValue, Status)).ToString() & "Png"), BitmapImage)

  22:     End Sub

23:

  24:     Public Property Radius() As Double

  25:         Get

  26:             Return Me.imgStatus.Height / 2

  27:         End Get

  28:         Set(ByVal value As Double)

  29:             Me.imgStatus.Width = value * 2

  30:             Me.imgStatus.Height = Me.imgStatus.Width

  31:         End Set

  32:     End Property

33:

  34:     Private _vy As Double

  35:     Public Property VY() As Double

  36:         Get

  37:             Return Me._vy

  38:         End Get

  39:         Set(ByVal value As Double)

  40:             Me._vy = value

  41:         End Set

  42:     End Property

43:

  44:     Private _vx As Double

  45:     Public Property VX() As Double

  46:         Get

  47:             Return Me._vx

  48:         End Get

  49:         Set(ByVal value As Double)

  50:             Me._vx = value

  51:         End Set

  52:     End Property

53:

  54:     Private _mass As Double

  55:     Public Property Mass() As Double

  56:         Get

  57:             Return Me._mass

  58:         End Get

  59:         Set(ByVal value As Double)

  60:             Me._mass = value

  61:         End Set

  62:     End Property

63:

  64:     Private _x As Double

  65:     Public Property X() As Double

  66:         Get

  67:             Return Me._x

  68:         End Get

  69:         Set(ByVal value As Double)

  70:             Me._x = value

  71:         End Set

  72:     End Property

73:

  74:     Private _y As Double

  75:     Public Property Y() As Double

  76:         Get

  77:             Return Me._y

  78:         End Get

  79:         Set(ByVal value As Double)

  80:             Me._y = value

  81:         End Set

  82:     End Property

83:

  84: End Class

85:

86:

Once I had the particle class created, I decided to use a variation of a spring physics equation to get the desired float animation. The spring equation forces the particles toward each other and then springs them past each other similar to how a ball on the end of a rubber band would act when pulling it and letting it spring back and forth. Then by tweaking the force and velocity applied to each particle I successfully simulated a floating effect (I am by no means a physicist and I am sure there is a better way of implementing this equation). By combining the CompositionTarget.Rendering event and the positioning logic we can effectively scatter and animate the particles on our Canvas. The math involved looks something like this:

   1: void Spring(Particle a, Particle b)

   2:         {

   3: double dx = b.X - a.X;

   4: double dy = b.Y - a.Y;

5:

   6: double dist = Math.Sqrt(dx * dx + dy * dy);

   7: if (dist < _minDist)

   8:             {

   9: double ax = dx * _spring;

  10: double ay = dy * _spring;

11:

  12:                 a.VX += ax;

  13:                 a.VY += ay;

14:

  15:                 b.VX -= ax;

  16:                 b.VY -= ay;

17:

  18: Canvas.SetLeft(a, a.X);

  19: Canvas.SetTop(a, a.Y);

20:

  21: Canvas.SetLeft(b, b.X);

  22: Canvas.SetTop(b, b.Y);

23:

24:

  25:             }

26:

  27: Canvas.SetLeft(a, a.X);

  28: Canvas.SetTop(a, a.Y);

29:

  30: Canvas.SetLeft(b, b.X);

  31: Canvas.SetTop(b, b.Y);

32:

33:

  34:         }

35:

  36: VB:

  37: PrivateSub Spring(ByVal a As Particle, ByVal b As Particle)

  38: Dim dx AsDouble = b.X - a.X

  39: Dim dy AsDouble = b.Y - a.Y

40:

  41: Dim dist AsDouble = Math.Sqrt(dx * dx + dy * dy)

  42: If dist < _minDist Then

  43: Dim ax AsDouble = dx * _spring

  44: Dim ay AsDouble = dy * _spring

45:

  46:             a.VX += ax

  47:             a.VY += ay

48:

  49:             b.VX -= ax

  50:             b.VY -= ay

51:

  52:             Canvas.SetLeft(a, a.X)

  53:             Canvas.SetTop(a, a.Y)

54:

  55:             Canvas.SetLeft(b, b.X)

  56:             Canvas.SetTop(b, b.Y)

57:

58:

  59: EndIf

60:

  61:         Canvas.SetLeft(a, a.X)

  62:         Canvas.SetTop(a, a.Y)

63:

  64:         Canvas.SetLeft(b, b.X)

  65:         Canvas.SetTop(b, b.Y)

66:

67:

  68: EndSub

69:

  70: And the main animation loop looks like this:

71:

  72: C#:

  73: void CompositionTarget_Rendering(object sender, EventArgs e)

  74:         {

  75: for (int i = 0; i < _numParticles; i++)

  76:             {

  77:                 _particles[i].X += _particles[i].VX;

  78:                 _particles[i].Y += _particles[i].VY;

79:

  80: Particle p = _particles[i];

81:

  82: if (p.X >this.Width)

  83:                 {

  84:                     p.X = 0;

  85:                 }

86:

  87: elseif (p.X < 0)

  88:                 {

  89:                     p.X = this.Width;

  90:                 }

91:

  92: if (p.Y >this.Height)

  93:                 {

  94:                     p.Y = 0;

  95:                 }

  96: elseif (p.Y < 0)

  97:                 {

  98:                     p.Y = this.Height;

  99:                 }

 100:             }

 101:

 102:

 103: for (int i = 0; i < _numParticles - 1; i++)

 104:             {

 105: var partA = _particles[i];

 106: for (int j = i + 1; j < _numParticles; j++)

 107:                 {

 108: var partB = _particles[j];

 109:                     Spring(partA, partB);

 110:

 111:                 }

 112:             }

 113:         }

   1: Sub CompositionTarget_Rendering(ByVal sender As System.Object, ByVal e As System.EventArgs)

   2: For i AsInteger = 0 To _numParticles - 1

   3:             _particles(i).X += _particles(i).VX

   4:             _particles(i).Y += _particles(i).VY

5:

   6: Dim p As Particle = _particles(i)

7:

   8: If p.X >Me.Width Then

   9:                 p.X = 0

10:

  11: ElseIf p.X < 0 Then

  12:                 p.X = Me.Width

  13: EndIf

14:

  15: If p.Y >Me.Height Then

  16:                 p.Y = 0

  17: ElseIf p.Y < 0 Then

  18:                 p.Y = Me.Height

  19: EndIf

  20: Next i

21:

22:

  23: For i AsInteger = 0 To _numParticles - 2

  24: Dim partA = _particles(i)

  25: For j AsInteger = i + 1 To _numParticles - 1

  26: Dim partB = _particles(j)

  27:                 Spring(partA, partB)

28:

  29: Next j

  30: Next

31:

  32: EndSub

33:

Supporting Multiple Monitors

After the animation was rendering correctly the next step was getting it to run on multiple monitors. To make this happen I wrote some code in the application entry point to get a handle to the active screens. The System.Windows.Forms namespace has a Screen class which contains a collection of screens and their attributes including working area, width, and height. By looping through the screen collection I measure the screen boundaries and set the window size dynamically based on the available screen real estate.

   1: private void Application_Startup(object sender, StartupEventArgs e)

   2:         {

3:

   4: Window1 _window = null;

5:

   6:             System.Windows.Forms.Cursor.Hide();

7:

   8: foreach (Screen screen inScreen.AllScreens)

   9:             {

  10: if (screen.Primary)

  11:                 {

  12: Rectangle location = screen.Bounds;

  13:                     _window = newWindow1(location.Height, location.Width);

  14:                     _window.Width = location.Width;

  15:                     _window.Height = location.Height;

  16:                     _window.Left = 0;

  17:                     _window.Top = 0;

  18:                     _window.WindowState = WindowState.Maximized;

  19:                     _window.Show();

  20:                 }

21:

  22: elseif (!screen.Primary)

  23:                 {

24:

  25: Rectangle location = screen.Bounds;

  26:                     _window = newWindow1(location.Height, location.Width);

  27:                     _window.Left = screen.WorkingArea.Left;

  28:                     _window.Top = screen.WorkingArea.Top;

  29:                     _window.Width = location.Width;

  30:                     _window.Height = location.Height;

  31:                     _window.Show();

  32:                 }

33:

  34:             }

35:

  36:         }

   1: private void Application_Startup(object sender, StartupEventArgs e)

   2:         {

3:

   4: Window1 _window = null;

5:

   6:             System.Windows.Forms.Cursor.Hide();

7:

   8: foreach (Screen screen inScreen.AllScreens)

   9:             {

  10: if (screen.Primary)

  11:                 {

  12: Rectangle location = screen.Bounds;

  13:                     _window = newWindow1(location.Height, location.Width);

  14:                     _window.Width = location.Width;

  15:                     _window.Height = location.Height;

  16:                     _window.Left = 0;

  17:                     _window.Top = 0;

  18:                     _window.WindowState = WindowState.Maximized;

  19:                     _window.Show();

  20:                 }

21:

  22: elseif (!screen.Primary)

  23:                 {

24:

  25: Rectangle location = screen.Bounds;

  26:                     _window = newWindow1(location.Height, location.Width);

  27:                     _window.Left = screen.WorkingArea.Left;

  28:                     _window.Top = screen.WorkingArea.Top;

  29:                     _window.Width = location.Width;

  30:                     _window.Height = location.Height;

  31:                     _window.Show();

  32:                 }

33:

  34:             }

35:

  36:         }

Making it a Screen Saver

The last step to this application is making it a screen saver. By implementing mouse and keyboard event handlers to shut down the application we essentially can mimic the interaction of a screen saver.

   1: MouseMove += newMouseEventHandler(Window2_MouseMove);

   2:   MouseDown += newMouseButtonEventHandler(Window2_MouseDown);

   3:   KeyDown += newKeyEventHandler(Window2_KeyDown);

   4: void Window2_KeyDown(object sender, KeyEventArgs e)

   5:         {

   6: Application.Current.Shutdown();

   7:         }

8:

   9: void Window2_MouseDown(object sender, MouseButtonEventArgs e)

  10:         {

  11: Application.Current.Shutdown();

  12:         }

13:

  14: void Window2_MouseMove(object sender, MouseEventArgs e)

  15:         {

  16: Point currentPosition = e.MouseDevice.GetPosition(this);

17:

  18: if (!isActive)

  19:             {

  20:                 mousePosition = currentPosition;

  21:                 isActive = true;

  22:             }

  23: else

  24:             {

25:

  26: if ((Math.Abs(mousePosition.X - currentPosition.X) > 10) ||

  27:                     (Math.Abs(mousePosition.Y - currentPosition.Y) > 10))

  28:                 {

  29: Application.Current.Shutdown();

  30:                 }

  31:             }

  32:         }

   1: AddHandlerMe.MouseMove, AddressOf Window_MouseMove

   2: AddHandlerMe.MouseDown, AddressOf Window_MouseDown

   3: AddHandlerMe.KeyDown, AddressOf Window_KeyDown

4:

   5: PrivateSub Window_KeyDown(ByVal sender AsObject, ByVal e As KeyEventArgs)

   6:         Application.Current.Shutdown()

   7: EndSub

8:

   9: PrivateSub Window_MouseDown(ByVal sender AsObject, ByVal e As MouseButtonEventArgs)

  10:         Application.Current.Shutdown()

  11: EndSub

12:

  13: PrivateSub Window_MouseMove(ByVal sender AsObject, ByVal e As MouseEventArgs)

  14: Dim currentPosition As Point = e.MouseDevice.GetPosition(Me)

  15: If (Not isActive) Then

  16:             mousePosition = currentPosition

  17:             isActive = True

  18: Else

  19: If (Math.Abs(mousePosition.X - currentPosition.X) > 10) OrElse (Math.Abs(mousePosition.Y - currentPosition.Y) > 10) Then

  20:                 Application.Current.Shutdown()

  21: EndIf

  22: EndIf

  23: EndSub

24:

Lastly, simply set the build configuration to Release mode and build it. In the output bin->Release directory find the built executable. Rename the file extension from .exe to .scr then right click and choose Install from the context menu.

That's it!

Challenges to You

One of the interesting things about Office Communicator Server is that it comes with an SDK to build your own custom Unified Communications applications.

I would love to see the presence bubbles actually hooked up to real users' status, and maybe a cool animation to indicate when a users' status is changed.
Create a config file to let the user specify his/her own images and tweak other settings like speed and velocity.

Conclusion

This was a great opportunity to brush up on my physics skills and play with some of the animation possibilities in WPF. This application is also a great example of alternative data visualization. Sometimes I get tired of seeing everything in tabular form and I think that “presence art” is a great example of Art + Code (aesthetically pleasing and functional). I hope you enjoy it.

Channel 9