[joaquimandrade]

I had this idea also (and I think that it has also implemented in HLGuard) and the true is: it is almost impossible to make it right without a huge amount of calculations and probably that will make it laggy with many users. One particular point where calculations are missing is in checking if the player carried weapon is visible (what is out of the player's bounding box). That will easily damage the game. And, as Exolent said particular, entities or map, designs can make it behave bad.

Edit: I have an simple idea to you. Instead of shipping it as an anti-wallhack solution, you could make it usable when you perform an action. Example: you suspect that a player is cheating, enable it on him, and check if his performance hugely differs.

One thing about the code: In traceline you should "IGNORE_GLASS".