Creating Killer Animations in Code - Page 5
       by kirupa  |  17 October 2009

In the previous page, I briefly explained how the code works before diving into the code itself. In this page, let's finish explaining the code and wrap any loose ends up.


The line we stopped at in the previous page is the following:

if (System.ComponentModel.DesignerProperties.GetIsInDesignMode(this) == false)
{
CompositionTarget.Rendering += new EventHandler(AnimateCircle);
}

If there is one thing you remember from this tutorial it is this - hooking into the Rendering event is one of the best ways to create a loop for an animation that does not block or freeze your application. At every screen refresh, a method that you specify gets called. Needless to say, that method is going to get called a whole lotta times every second.

You access the rendering event as follows:

CompositionTarget.Rendering += new EventHandler(AnimateCircle);

Just like any event you will encounter in .NET, you have to associate it with an event handler that will get called each time the event fires. In our example, that event handler is called AnimateCircle. The AnimateCircle method gets called numerous times each second because the Rendering event fires numerous times each second, so any code that you want to use for simulating your animation, you would want to place inside your AnimateCircle movie clip.


Let's look at our AnimateCircle method next:

void AnimateCircle(object sender, EventArgs e)
{
angle += speed/10;
 
Canvas.SetTop(this, yPos + 50 * Math.Sin(angle));
Canvas.SetLeft(this, xPos + 50 * Math.Cos(angle));
 
if (angle >= 2 * Math.PI)
{
angle = 0;
}
}

The AnimateCircle method is responsible for actually adjusting the x and y positions, and that is done via the Canvas.SetTop and Canvas.SetLeft function. These are the opponents, if you will, of the Canvas.GetTop and Canvas.GetLeft function that you saw earlier.

I am not going to delve into the mechanics of the animation itself, but you can get an overview of the type of animation by looking into the first few non-ActionScript related pages of the Trigonometric Animations tutorial. One thing I mentioned earlier is that our speed value is being set at a very small number. While the number is very small, because we are incrementing the angle variable by the speed property in a method that gets called hundreds of times every few seconds, everything balances out.

Adding More Circles
Currently, you only have one lone circle in your animation. In Blend, make sure MainPage.xaml is currently opened. Select the lone circle usercontrol that you see, copy it by pressing Ctrl + C (or using the right-click menu), and paste it a bunch of times. Your Objects and Timeline panel will look as follows with many instances of your BlueCircle usercontrol displayed:

[ you can never have too many circles...that are blue! ]

On the design surface, feel free to move each circle around, alter its sizes, etc. Be creative. Here is what my design surface looks like:

[ be creative in your placement and look of the circles ]

Because each usercontrol is a self-contained animation with a copy of all of the code that you saw in the preceding pages, simply hitting F5 is all you need to after you paste/rearrange all of the circles to seem them all movie in their own random, circular way.


Conclusion
Well, that is all there is to creating code-based animations in Silverlight and WPF. There basically three things you need to follow:

  1. Ensure your UserControl has fully loaded by hooking up the Loaded event with an event handler.

  2. Inside your Loaded event's event handler, setup the Rendering event and associate that with an event handler that will process the Rendering events.

  3. Place any code that will be responsible for continuously updating the properties that will make up your animation inside the event handler for the CompositionTarget.Rendering event.

  4. Go crazy. Very rarely will you ever have the opportunity to easily combine math with programming to create something beautiful and engaging. Take advantage of these rare moments.

To see how my version looks, as always, you can download the source files from below:

Download Source Files

If you have a question about this or any other topic, the easiest thing is to comment below or drop by our forums where a bunch of the friendliest people you'll ever run into will be happy to help you out!

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