First Look: Silverlight 2.0 UI Controls
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by Todd Anglin
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Media Controls

Navigation and Input controls are essential to making any application work, but it is usually the media controls that really give an application its visual appeal. Silverlight provides a diverse array of media controls for displaying everything from basic images to the snazzy Deep Zoom images. Let's take a look at how Silverlight's UI controls enable us to display media in our beta applications.

Image

How do you display an image in a Silverlight application? With the Image control, of course. And while you may be quick to dismiss the Image control as nothing special (I did), there are some interesting properties on this control you should be aware of, especially if you're coming from the web world. First, make a mental note: Silverlight only supports JPEG and PNG images. Sorry GIF purists, you're currently out of luck. If you try to use a GIF image in Silverlight, an application exception will be thrown.

To display an image, you need to set the Source property of the Image control. The Source property can be set to one of two things: the relative path to an image located in your Silverlight project or to an instance of the BitmapImage class set in the code behind. If you try to set the source directly to an image on the web (like, http://www.something.com/images/myimage.png) Silverlight will crash. For scenarios like that, you can use the BitmapImage in your code behind to build a new image based on a URI or stream.

Listing 20 shows a basic image control in a Silverlight application displaying an image located in the Silverlight project. When the project is built, the image is packaged in to the Silverlight XAP file (basically a ZIP archive with the Silverlight specific .xap extension that represents a deployable Silverlight application), so you don't have to worry about deploying your images separately from your Silverlight application.

Listing 20 - Silverlight Image

<Image Stretch="None" Source="images/anxious.jpg"></Image>

Listing 20 also highlights another unique property of the Image control: Stretch. You can set this to one of four enumerated values: None, Fill, Uniform, or UniformToFill. Clearly, "None" is the default value and it renders an image in its original dimensions. The other values will stretch the image, proportionally or not, to fill its parent container.

Also, don't forget about some of the Image controls inherited properties, like Opacity. By setting this value to anything less than 1 you can easily make your image translucent. Pretty cool! Now if only other image transformations were so easy…Image.AutoCrop().FixColor().MakeInteresting(). Maybe in Silverlight 3.0.

MediaElement

While the Image control is used for displaying static images, the MediaElement UI control is your tool of choice for "displaying" audio and video clips in your Silverlight app. It has a number of unique properties and events that allow you to take control over your media and handle downloading/buffering. Going in depth on these properties is an article unto itself, but at the highest level you need to know that, like the Image control, the MediaElement exposes a Source property that must be set to the URI of your content.

The MediaElement only supports Windows Media Video, Windows Media Audio, and MP3 formats (of varying flavors). The control also offers support for streaming if you're using a Windows Media Streaming server and limited support for Advanced Media Redirector (a.k.a. Windows Media metafiles) files. Neither of these extends Silverlight's format support, but they give you more control over how you distribute your media.

Listing 21 shows a basic MediaElement control hosting a sample Windows Media Video. Unlike the Image control, videos won't automatically get packaged in to your XAP file, which can cause some headaches when you first start playing with the control. Instead, you need to manually copy your video files to the ClientBin directory in your website for the MediaElement to find them (in the following example, WindowsMedia.wmv is in the root of ClientBin).

Listing 21 - Silverlight MediaElement

<MediaElement Source="WindowsMedia.wmv" AutoPlay="True" Opacity=".7">
</MediaElement>

The MediaElement also has support for Triggers. Triggers are essentially "bookmarks," or "chapters," that you can define for any media in the MediaElement. Typically you'd configure these ahead of time and embed them in the media (with a program like Windows Media File Editor), but you can create them dynamically be defining a collection of TimelineMarkers and passing them to the MediaElement's Markers property. Regardless of when they're created, each time a marker is reached during media playback the MediaElement's MarkerReached event fires, giving you the opportunity to create rich media playback environments.

MultiScaleImage

The MultiScaleImage control is perhaps the worst named control in the current Silverlight 2 UI controls collection. The control is really the required front-end tool for taking advantage of Silverlight's new Deep Zoom technology (formerly Sea Dragon in MS Labs). Deep Zoom enables you to display HUGE images on the web in a ZUI (zoomable user interface) with smooth, animated transitions that give the illusion of seamless image zooming.

Deep Zoom images are created using a tool called, aptly, the Deep Zoom Composer. The tool takes a large image (or multiple large images) and processes them in to many smaller image "tiles" that are organized in number of folders. Each folder represents a different "layer" in the final composition. It is this collection of folders and image tiles that the MultiScaleImage references and pieces together for you in your Silverlight application.

To configure the MultiScaleImage, you simply set the Source property to location of the .bin file generated by the Deep Zoom Composer. You'll need to make sure you copy all of the folders to your ClientBin directory (or wherever you chose to host your files) in addition to the .bin file. In Listing 22, the .bin file is in the "ToddPortrait1_vandalized" directory, which is in the root of ClientBin and also contains all of the Deep Zoom generated content. If everything is configured correctly, you should see your image "zoom in" to view when your application loads.

Listing 22 - Silverlight MultiScaleImage

<MultiScaleImage Source="ToddPortrait1_vandalized/info.bin" 
      ViewportWidth="1.0" Width="300" Height="300">
</MultiScaleImage>

The ViewportWidth property, set to "1.0" in Listing 22, controls the MSI's zoom factor. The default value is 1, which means the image will be displayed at a size that fits everything on the screen. The closer the number supplied to ViewportWidth gets to zero, the more zoomed the image will be. In other words, if we simply change the ViewportWidth to ".5" instead of "1.0," when the image loads it will be more zoomed-in (Listing 23). You can also set numbers larger than 1, but as you do the image will simply appear smaller on the page. A little backwards and confusing, I know.

Listing 23 - ViewportWidth zoomed

You can also set the ViewportOrigin property, which obviously adjusts where the image is focused when it loads. That helps you solve problems like the focus of the image above. There is also a UseSprings property that you'll discover on the MSI control. This enables you to disable the Deep Zoom animations- a big part of what makes the technology "sing"- so you'll probably rarely find a reason to set this to false.


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User Comments

Title: how to embbed images in canvas ?   
Name: andrew
Date: 2008-10-11 12:39:36 PM
Comment:
Is there a way to put images in canvas based on logic ?






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