GNOME applications currently follow two different metaphors regarding the relationship between documents and windows. Some applications use a Single Document Interface (SDI) as recommended by the HIG, i.e. one window per document, as for example evince, nautilus, eog, and inkscape. The first two also obey spatial behavior, i.e. they remember window position and size per document resp. folder. Other applications use a Multiple Document Interface (MDI), i.e. one window by default and one tab per document, examples: gedit, epiphany, firefox, devhelp. This week I had the idea of a third way that might work well for most applications.
SDI is very simple to use and quite convenient when combined with spatial behavior as you can arrange your document windows how you like it and you’ll see your documents exactly the same each time you open them. The main disadvantage of SDI is that you end up with many windows, one for each open web page, folder, conversation, text file, and more. The window list applet and the Alt+Tab window switcher don’t scale well, you spend a lot of time finding your window when you have several dozens of windows open.
That’s why some applications use MDI. You’re able to manage your documents or web pages on two levels, that means the window list applet and Alt+Tab are a lot more useful again. A disadvantage is that the configuration of your windows vanishes when you close the window. This may mean that you keep your windows open relatively long, also across logout/login, so that you don’t have to arrange your windows that often. You end up with quite a lot of open windows, again, using more memory and taking time when restoring your session.
My idea now tries to combine the main advantages of the two approaches by making windows first-class objects. So instead of treating windows and documents as the same or forgetting about a window as soon as it’s been closed, treat windows as separate objects. I want you to care about your windows, give each of your window a name, an icon, maybe even a special color for the window frame. Windows should be persistent: if you close a window, its name, icon, position, size, and content should be kept. You can open this window again by using the name and icon you’ve chosen. Creating and destroying – in contrast to opening and closing – a window should be a conscious action, not something that happens as a side-effect of something else; there will be exceptions, of course.
A more concrete proposal follows: Replace the window list applet by something like the dock in Mac OS X with the big difference that it’s about windows instead of applications. The main part is a persistent list of icons of open and closed windows; the windows are stored as desktop files. If you click on an icon and the window isn’t open yet, it will be opened, i.e. like a launcher but you get your documents back. If the window is already open, it just activates the window. To the right of this icon list is a list of currently open non-persistent windows, just like the current window list applet.
Metacity should also have knowledge of the persistent windows and set the visible window title and icon according to the user’s configuration. Applications should use tabbed MDI as basis and add support for restoring windows by name – similar to the session restore feature already implemented in many applications.
Does this make sense or am I missing something substantial? I’ve implemented a proof of concept applet in Vala and patched epiphany to work as described, will import it into some repository later, if there is interest.