This is a stock version of dwm that includes the "canvas" mode seen in
vxwm. vxwm is built on dwm. Generate a patch below, the patch will add
the canvas mode and show the coordinates of the canvas in the dwmbar.

I've provided a canvas.patch file which you can download to your dwm
build. To instead generate the patch file from scratch you can run
the patch.sh file or you can view the contents of it to figure out
how to generate the patch file.

Once you have the canvas.diff file (either from generating it
yourself or downloading the pre-made one, you can apply the patch
as you would any other dwm patch:
patch -F3 -i canvas.diff

Recompile dwm (don't forget to cat config.def.h > config.h) and it
should work fine. Check your dwm config.def.h file for the default
keybinds.

Again, this feature was taken directly from vxwm, which is a dwm fork
that comes with patch management and a canvas mode, so for more details
please go and review the code or changes in vxwm:
https://codeberg.org/wh1tepearl/vxwm