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j3 - window management hotfix

copyright 2013, Jake Teton-Landis. All rights reserverd.

The goal of j3 is to suplement an existing window manager that you already use and enjoy, by adding a few small window managemnt behaviors for the mouse.

j3 should work with any EWMH-compliant, floating-style window manager. The primary host window manager target is Fluxbox, but I intend to add support for tiling window managers like i3 at some point.


j3 currently has 3 window management actions. These actions are preformed by dragging a window (the incoming window) over another window (the target window), and releasing the mouse over one of several j3 drop targets.

  1. Swap


    Drag a window onto the center swap of another window to swap the positions and sizes of two windows

  2. Split

    Split - Top Split - Right Split - Bottom Split - Left

    Drag a window onto any of the split icons to split the target window in half. The incoming window will take the highlighted half, as indicated on the icon, leaving the target to fill the other half.

  3. Shove

    Shove - Top Shove - Right Shove - Bottom Shove - Left

    Drag a window onto any of the shove icons to move the incoming window to that side of the target window. The incoming window will be resized so that its edges are flush with the target.


To build j3, you must have a Go runtime, and development headers for your X11 window server. For more information on X11 development with Go, please see The X Go Binding.

j3 is a go-installable go program. If you already have Go, then you can just run

$ go get -u

If you don't have Go installed already, the Go downloads page has pretty good instructions to get you started.

After installation, just run j3 & disown to start the manager.


j3 only responds to special key combinations. By default, the key combination is Option-Shift in combination with a left-mouse-button drag. This key combination can be changed by modifying the KeyCombo constant at the top of executable.go and re-installing j3.


We can seperate the issues into j3 into two categories: additional features, and improvements to the present behavior. Here are the features that I am interested in adding:

Seam resizing

Seam-based resizing. The user should be able to resize adjacent windows at the same time by dragging on the shared edge between the windows. Right now the "split" action is still rather cumbersome if you are using a floating window manager: if you want a different ratio, you can use the split to start your layout, but you must then resize and move both windows to achieve layout zen.

My plan for seam resizing is to implement the following algorithm, and bind it to a different key combination than the current window movement action.

    incoming = window-under-mouse()
    coords = get-mouse-coordinates()
    edge = incoming.edge-closest-to(coords)

    target = ->
        for win in get-managed-windows():
            if win.has-edge(edge):
                return win

    if target isnt nil:
        seam-manager.start_drag(incoming, edge, target)
        // perform-normal-rescale
        resize-manager.start_drag(incoming, edge)



I don't really want to be testing if the mouse is over an edge, so we'll do this Fluxbox style with resize-from-anywhere by detecting what edge the mouse is closest to, by drawing an [X] across the window to divide it into directional quadrants

Usability improvements

  • Display an icon while dragging the window

  • hide the move window UI when the mouse leaves a window to the desktop

  • handle overlapping windows.

    This is a difficult problem. If we have two indows like this:

      |                            |   
      | OUTER                      |     
      |   _______________          |     
      |   |               |   
      |   | INNER         |   
      |   |               |   
      |   |               |   
      |   |               |   
      |   |               |   
      |   | _____________ |   
      |                            |     
      |                            |     
      |                            |     
      | ___________________________|

    How can we properly target OUTER with the UI, when it will be placed over INNER?

    This is a question that seems difficult to answer without introducing more state into the program


j3 helps your window manager suck a little less. Not for tiling WMs yet :(



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