Undefined Fire

It took a lot longer than expected but the KWin window tabbing branch has finally been merged with trunk. This now means that it is possible to manually merge multiple windows together by middle-click dragging the titlebar of one window over another.

Since the branch was not trivial a large "thank you" has to go out to the Google Summer of Code student Jorge Mata for his initial hard work on making KWin support tabbing. Not only that but another "thank you" has to go out to Hugo Pereira Da Costa from the Oxygen team for actually making a tabbing-compatible decoration that's not ugly and helping me find all the little annoying bugs in the decoration API along the way. ^_^;

There seems to be a common misconception as to what this KWin branch actually provides so let me explain it in slightly more detail. This branch allows the user to merge two or more windows (They can belong to the same application or not, it doesn't matter) so they all share the same decoration but it does not allow applications to automatically add new tabs or modify the existing ones in its own decoration—it doesn't even know that the window is tabbed to begin with. This means no Khromium for you yet.

To actually have the application control the window tabs is slightly more complex that it first looks. To prevent application regressions the window manager will have to add support for the application to add extra menu items to the context menu for things such as page bookmarking or reloading for example in the case of a browser. Not only that but as the application would most likely want to be able to work with window managers that don't support tabbing they will need to write fallback methods as well. It is actually far more portable and less complex if the application renders its own decoration from the start and it is for this reason why I'm slightly against adding support for application-controlled window tabs in the window manager.

Other than some very minor visual glitches here and there when using the Oxygen decoration (That you probably won't even know existed if I didn't just mention it) there is only three bugs that I know about that relate to window tabbing:

1. Window shading of grouped windows doesn't work properly,
2. Grouped windows won't remember their tab order on KDE session restore, and
3. Some desktop effects don't correctly handle grouped windows.

Since we've been working on this for so long we might have forgotten something obvious in its implementation (Maybe a keyboard shortcut or something; I dunno). If you find anything please report it ASAP to the KWin component on bugs.kde.org, especially if it requires UI changes as string freeze is a little over a week away!