Debugging a Window Manager (Xorg)

Hi! this will be a short post to help future window manager hackers. I’m currently developing a window manager and was having trouble debugging it from a TTY (yes, from TTY). After a bit of searching, I find the Xephyr.

Xephyr - A Nested X Server

Xephyr is the best way to test and run a window manager. It basically runs an X server inside a window.

Installation (Arch Linux, Void Linux)

$ sudo pacman -S xorg-server-xephyr

$ sudo xbps-install xorg-server-xephyr

Usage

$ Xephyr -screen 1280x720 :1

Create a nested X server window with size 1280x720 and display name “:1”.

Launching applications

$ DISPLAY=:1 dwm

Launch the dwm in display “:1”.

To launch an application, specify the display followed by the application command.

Grabbing and un-grabbing user input

Pressing Ctrl+Shift should lock/unlock your mouse pointer and your keystrokes inside Xephyr window exclusively if possible.

Reference

https://wiki.archlinux.org/title/Xephyr

C - Preprocessors

I could end this post here, but I want to share a useful way for logging in your application using C preprocessors:

#include <stdio.h>

#define LOG(str) printf("app --> %s\n", str);

int main() {
  int err = 0;

  // ...

  #ifdef LOG
  LOG("<log> main();")
  if (err)
    LOG("<error> main();")
  #endif

  return 1;
}

C preprocessors enable conditional code inclusion based on macro definitions (Conditional Compilation).

Tadah! Now you can enable or disable the log system simply by commenting or uncommenting the #define LOG line. Of course, you can also apply this strategy using a library like log.c.