Center Window on the Current Monitor in Emacs, Simplified

Apr 22nd, 2022

Louis Brauer over on Xah Lee’s Discord helped simplify my Emacs window centering code (cf. original single monitor solution. It’s great, and only a handful of lines!

It’s compatible with Emacs 26.0.90 (reference commit or newer:

(defun my/frame-recenter (&optional frame)
  "Center FRAME on the screen.
FRAME can be a frame name, a terminal name, or a frame.
If FRAME is omitted or nil, use currently selected frame."
  (interactive)
  (unless (eq 'maximised (frame-parameter nil 'fullscreen))
    (modify-frame-parameters
     frame '((user-position . t) (top . 0.5) (left . 0.5)))))

That is, uh, very simple in comparison to my old approach where I computed the center of the frame inside the monitor’s manually!

All credit goes to Luis for this.

Links to this article

Automatically Center New Emacs Windows (Aka Frames) on Screen

When I open a new GUI window of Emacs on macOS (which Emacs calls frame) it’s positioned in the top-left corner. Since I have an ultrawide monitor at my desk, that’s pretty annoying. Unlike regular macOS apps, Emacs doesn’t remember where I dragged the last NSWindow to, so it doesn’t spawn new windows next to that. It also doesn’t stagger them like NSDocument-type apps usually do.
Multi-Monitor Compatible Code to Center Emacs Frames on Screen

When centering my Emacs windows (aka ‘frames’) on my monitors, I noticed that with 2 monitors active, the computation doesn’t work: It doesn’t center in the main monitor; it centers in the area of both monitors combined. That’s not what I want.