Microsoft's Silverlight started out as a Flash competitor, but has evolved into a cross-platform way of delivering .NET and Windows Presentation Foundation (WPF) applications both in and out the browser. Unlike other Microsoft programming tools, tied to the three-yearly cycle of Visual Studio releases, Silverlight is being developed in internet time, with version 4 less than a month from release.
A beta of Silverlight 4 was unveiled at Microsoft's PDC developer conference back in November 2009. This week saw the release candidate launched at MIX10. Like earlier versions of Silverlight, Silverlight 4 is delivered as a web browser plug-in, with support for all the major browsers (Google Chrome support being added with Silverlight 4). The download remains small, of the order of 5MB, and Microsoft currently claims that 60 percent of all internet-connected devices are running a version of Silverlight.
Video and media remain important parts of Silverlight, and Microsoft is following Adobe's lead and open-sourcing the components used to build the Silverlight video player used by major media outlets. It's also increasing Silverlight's DRM support, with support for a protected video path, making sure that video is managed securely all the way to the monitor.
As well as its video support, Microsoft is stressing the business applications of Silverlight 4, and has improved its printing and graphics capabilities in the release candidate. One of the more important features is the addition of support for Live Labs' Pivot data visualisation and exploration tool, which uses the Deep Zoom technologies already in Silverlight to work with large and complex data sets. Hardware acceleration will be used to speed up complex graphic tools like Deep Zoom and Pivot.
Silverlight 3 introduced basic out-of-browser operation. Silverlight 4 takes it still further, introducing a class of trusted applications that get access to more system resources on the host PC or Mac, like user folders, notification windows and COM interaction with other apps (like exporting data to Word or Excel). These applications do need to be digitally signed before the Silverlight runtime grants access to these additional functions. Out-of-browser applications can now also use their own look and feel, replacing the default chrome with their own. One example of this is eBay's listing application, which uses Silverlight to give a clean, clear cross-platform look and feel on both Mac and PC.
The desktop Silverlight 4 is not the same Silverlight as is used to deliver Windows Phone 7 Series applications. That's currently an interim version, based on Silverlight 3 with some Silverlight 4 functions. An upgrade to a mobile version of Silverlight 4 will be possible using Windows Phone’s over the air update tools, but a timescale hasn't been announced. In a much quieter announcement, Microsoft has also released a version of Silverlight for Nokia phones running Symbian. The performance optimisations from the mobile version will be added to the desktop Silverlight plug-in, possibly in an update and definitely by Silverlight 5.
The final release version of Silverlight 4 will launch at the same time as .NET 4, along with Visual Studio 2010. Microsoft promises full tooling support for Silverlight in its development platform, including a WYSIWG design surface. Designers using Microsoft's Expression Blend design tool will get a free upgrade from Blend 3 to Blend 4.