System/Display depended themeing and font config

[buhtz]

Dear David,
thanks a lot for your valuable work. What makes your Emacs content special is your way to explain things for absolute novices and professionell at the same time. I have not found that anywhere.

I am still at your Nr.6 video "Organizing Your Life with Org Mode" and also poked into some others. Maybe there still is a video taking my topic into account?

There are some technical detailed questions in my mind but backing them together would be a nice topic for a new video. I think you still discussed some aspects of it in some videos but not all together. The topic could be described as How to configure Emacs appearance independent from the used display and terminal/gui mode.

I use Emacs (I mean sharing the same init.el) on different "systems" and "displays" - sometimes direct/local, sometimes via remote desktop (XRDP) and SSH etc. It is very colorful. In that cases I often have problems with font size, screen resolution and DPI.

• direct: Debian 11, with 1920x1200 24-inch monitor
• via SSH: Lenovo ThinkPad Laptop with a 1920x1080 inbuild 14-inch display
• via XRDP ("use client resolution"): The same ThinkPad
• via SSH: The ThinkPad but connected to a ThinkVision 27-inch display with 2560x1440 resolution
• via XRDP ("use client resolution"): The ThinkPad connected to the ThinkVision monitor

Btw: Via SSH and XRDP most of the time the Emacs runs on a headless RapsberryPi 4 with Debian 11 and XFCE. Sometimes I also connect to the first machine (1920-1200 24-inch monitor) via XRDP or SSH from the ThinkPad Laptop.

So you see my problems? ;) I even do not fully understand the interplay between resolution and DPI. And what does Emacs know about my "display" and about the "terminal" or "X" currently using.

Technical questions in detail

• How to find out the relevant display informations in Emacs?
• How to find out if I am on terminal or gui mode?
• How to find out if I am via SSH, tty or terminal-emulation in X?
• How to configure fonts (face, size, other parameters) depending on that informations?
• How to use different themes depending on SSH, tty, term-emu or GUI mode?
• And if there are mode-specific font/theme settings (like you used in your org-mode video): How to take that into account?