scripting widgets for the Plasma Desktop

Before moving on with today's two entries in the "key quests" series, I wanted to note a couple of interesting things that have made it in KDE SC 4.4 when it comes to writing Plasma widgets, Plasmoids, in languages other than C++.

We've had rather nice Python and Ruby support for some time, thanks to Simon Edwards on Python, Richard Dale on Ruby and Carter Beauford on the drums .. wait, no, Carter is part of some other cool group, but Simon and Richard do indeed rock out with us. ;) While I think that these are great languages for writing full applications with, I also feel that there are possibly better choices for little plugins like Plasmoids. I won't get into all those reasons here (I probably have already done so in a past blog entry, though), but there you have it.

Unfortunately, those other choices, namely JavaScript and WebKit, haven't been so great. Things have improved a lot for the 4.4 release, however. The JavaScript API has been fleshed out and pretty seriously extended. Documentation is catching up as well. There are a few improvements in particular that wanted to highlight, however.

Run-Time Extensions For JavaScript Plasmoids

The first is the ability to request API extensions for JavaScript Plasmoids. The base API is meant to be pretty safe, so that it isn't overly scary to run code from $RANDOM_PLACE on your desktop. (There are a couple of loopholes still before I'm ready to call it "sandboxed", and those will be worked on in the next development cycle and should be part of the 4.5 release.) This means that there isn't access to network access, file dialogs, reading or writing files, etc. by default. This also rather limits what is possible. While a lot of the possible annoyances are alleviated by using a DataEngine, they don't cover all the bases. So starting in 4.4 you can put things like this in your metadata.desktop file:

X-Plasma-RequiredExtensions=FileDialog,http
X-Plasma-OptionalExtensions=LaunchApp

The entries case insensitive, and if security says "yes" then the extensions are activated and the API available to that instance of the widget grows accordingly. This also allows us to quite easily know which Plasmoids will be doing things like, well, opening files or launching applications. You can read about these extensions in the aptly named Extensions section of the API documentation or by looking at the http and fileOperations examples in the kdeexamples module.

In 4.5, we'll be offering additional capabilities including writing to files. There will likely be two levels to that: one that restricts a Plasmoid to writing to files in its own package and a more "full powered" one. The control over which extensions are allowed or not allowed will also be seeing some improvements in 4.5. DataEngines will also be getting tagged for security as right now DataEngine usage is wide open for all widgets and some of the DataEngines have gotten pretty powerful. Speaking of DataEngines, in 4.5 this same extension system is also available to DataEngines and search plugin Runners written in JavaScript.

WebKit Plasmoids Improve

Thanks to work done by Petri Damstén on the WebKit Plasmoid ScriptEngine, you can now do a lot more with the HTML and JavaScript derived widgets. Besides the things that QtWebKit provides, access to DataEngines and configuration values reading and writing are also available. Petri also knocked out some annoying bugs with the WebKit ScriptEngine along the way.

This resulted in people actually writing WebKit based Plasmoids which led to a feature request for Web Inspector support. QtWebKit made that insanely simple: a one line patch and the results are:



There is more to do with the WebKit ScriptEngine, but it's already pretty nice for the 4.4 release of the KDE Software Compilation. One of the biggest things lacking is documentation. We have two examples in kdeexamples now (the above screenshot is from one of them) and there is an introductory article on Techbase, but it's really embryonic still.