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

Logging system based on C macros

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

#include <stdio.h>

#define LOG(str)\
  printf("[%s:%i] %s\n", __FILE__, __LINE__, str);

int main() {
  int err = 1;

  #ifdef LOG
    if (err)
      LOG("error...");
  #endif

  return 0;
}

__FILE__: A macro that expands to the name of current input file. __LINE__: A macro that expands to the current input line number. https://gcc.gnu.org/onlinedocs/cpp/Standard-Predefined-Macros.html

This system uses the #ifdef and #endif macros to create a conditional compilation based on the #define LOG macro. You can enable or disable the logging system simply by commenting or uncommenting the #define LOG line. Of course, you can also apply this strategy using a library like log.c.