There is a nice article on Wikipedia that discusses the multiple document interface, a horrible hack that took hold in the Windows world to deal with the fact that Microsoft’s default window manager was inadequate to handle multiple windows existing under the same application.
I think Mac OS/OS X handles the MDI plague best by simply grouping all application windows under a single application class, with a single menubar. But usability experts have debated whether that makes the most sense, since the menubar can change, for example, depending on what window is in focus. I think users get used to that, and it also allows the menubar to be as long as necessary while the window can remain as small as necessary. That’s a nice win.
However, given our current model on *nix/Windows of menubars for every reasonably complex window, and given the lack of the MDI hack in GTK+, we do have a mess for applications that need more than one window to operate properly, i.e. Glade and The Gimp.
What I’ve been doing is giving these programs their own workspace as a workaround. That seems quite greedy of them, and indeed it is. What’s more, however, is that it’s unusable. Even when I switch to my Glade workspace, I see 4 windows in my taskbar, each with the same icon and with the following names: “Glade: h2h”, “Properties: image95”, “Widget Tree”, “h2h”. The first three are actually part of the Glade window class, and if I enable Metacity’s taskbar grouping, I see them as part of the same group. The last one, however, is just my actual window, and so is separate.
This is good–but I only get some form of usability when I actually enable window grouping. The thing is, in Metacity you can’t enable window grouping on a per-application basis. It’s all, sometimes, or nothing. Sometimes means metacity only groups windows when I’m running out of space. Otherwise it’s either on or off.
The thing is, grouping isn’t just about space saving. It’s about being able to perform window manager operations on a group of windows, i.e minimize all and maximize all.
This doesn’t even solve all problems: alt+tab still shows me all 4 glade windows, which can be quite confusing since only one comes into focus at a time. But that’s a separate issue, separate debate.
Wouldn’t it be nice if instead of Metacity just “figuring out” when to group my windows together, it let me just press a hotkey “Group all X windows on this workspace”, where X is the application I’m currently in?
I’ve decided this feature is so valuable, I may just hack metacity to add it. It will at least provide a path for solving the MDI nonsense.
Update: check out these screenies of a “different” approach to MDI written in GTK. It’s called GTK ADI.