How to Properly Maximize the Active Emacs Frame on Startup on Windows

I'm an avid GNU Emacs user and I like to have the active frame maximized at start-up. This is easily done on Linux:

(set-frame-parameter nil 'fullscreen 'maximized)

But on MS Windows this is not so trivial... Like many of you, I have to use Windows for my daily work. I tried many different approaches to get that frame maximized on Windows, but just recently I was able to achieve that outcome in a reliable manner that works across many different versions of Windows.

What worked!

In an effort to not bury the lead, as they say... this is what I have done that works:

(defun w32-maximize-frame ()
  "Maximize the current frame (windows only)"
  (interactive)
  (w32-send-sys-command 61488))

(if (eq system-type 'windows-nt)
    (progn
      (add-hook 'window-setup-hook 'w32-maximize-frame t))
  (set-frame-parameter nil 'fullscreen 'maximized))

In the above code I address maximizing the frame in the two platforms I use most: Linux and Windows. I defined the function w32-maximize-frame, which send the Windows message to the Emacs frame for it to maximize itself. The underlying function w32-send-sys-command is well-known, but initially it did not work for me as I'll explain below.

The strategy that did work for Windows was to wrap the call to w32-send-sys-command in a function and then add a call to it to the window-setup-hook. I tested this on the 7 and 8.1 versions of desktop Windows and on 2008 R2, 2012 versions of Windows Server and using Emacs 24.3. And if Emacs is not running on Windows, I set the frame parameter fullscreen to maximized for the current frame.

What didn't work...

I started this journey into figuring out how to start Emacs maximized a while back. In the beginning I would let Emacs start and then just use the maximize button on the title bar, but then I started using things like initial-frame-alist and set-frame-* to get the top, left and size just right for my different screens. The problem with that approach is that I had to tweak it for every new install of Emacs on every computer I used. It got old really quick.

Then I found the set-frame-parameter trick that you can see in the code above. But that only worked for Linux variants. At this point during my research, I have already found out about the w32-send-sys-command approach, but using it on my init.el file directly was not working. The frame would think itself as being maximized, and you could see that by looking at the state of the maximize button on the top-right of the window. But visually, the window would remain small.

Next I started using the maxframe.el package, but that really didn't last all that long. I found that there were several flaws with it: First, the package would not truly maximize the frame, but it calculates the size of the frame based on your monitor's resolution and font face sizes and stretch your frame accordingly; Second, the package would not account for the position of my XFCE desktop panel and place the Emacs title bar under it; And third, maxframe.el would not account for a multiple monitor setup and stretch the frame across my two monitors. So I dropped it and went back to the drawing board.

Conclusion

It turns out that the proper way to achieve the maximize frame on start-up on Windows is to use the window-setup-hook. This variable is a normal hook that Emacs runs after handling the initialization files. It turns out that with the previous approaches, I was trying to send a message in Windows to an Emacs frame that didn't yet exist. This hook is used for setting up communication with the windowing system and creating the initial window and is, therefore, the proper place, or point in time, to maximize our frame in Windows.