Walking on any surface?

I have a wild idea that is not really new, but it has been done before. I want to make a mod that allows you to walk on any surface in the game. I saw this done on youtube at this link:

does anyone know how this can be achieved?

That is an independent modification for half life 2 by someone that has not been released to the public. Unless garry hard-codes it into the game, you cannot do this.

The closest thing you’ll get to this in gmod is the gravity hull designator tool.