No, not that Windows. I’m talking about the ones that even Mac and Linux players have to deal with.
Many maps in TF2 feature glass windows, which surprisingly are something of a new feature for the TF series. Going back into Team Fortress Classic, I can’t find any examples in official maps of transparent screens allowing the user to look but not interact with further parts of the map. They were consciously included in TF2’s design, as the Gravelpit developer commentary explains:
“Height is a useful feature when designing defensible buildings. For instance, the cap B building needs to be defended from all directions. The height and windows at all sides give defenders in this building the advantage when launching rockets and grenades from within. Bulletproof glass and some windows lets them safely view approaching enemies.”
It’s actually quite interesting to look at windows from a conscious design perspective and not just take their existence for granted. A bulletproof window is a very powerful tool that can make or break a location in a map. It can heavily favor either offense (the windows overlooking the final point in Badlands) or defense (the windows overlooking the final point in Gorge) or both (the windows surrounding the final point in Junction). A duel completely changes when both players see the other coming before they can start killing each other.
A memorable event I can remember was in July 2013, when Valve updated, among other things, a window in Badlands mid so it was solid. The competitive community cried foul because this window was frequently used for assaulting the mid, escaping attackers, and even rollouts. Valve quickly reverted that change and even apologized for it in a later patch. This is a highlighting example showing how important a window can be.
But windows also matter in low level play for the opposite reason; a lot of new players don’t realize windows are invulnerable. Either they’re used to games with breakable windows like Call of Duty or they at least expect their bullets to penetrate like in Left 4 Dead 2. Making fun of new players who waste whole rounds shooting through windows is a time-treasured pastime.
But they’re not wholly unjustified in misunderstanding the concept behind a fragile pane of glass restricting them from shooting the dude they’re looking at. Would breakable windows work in TF2? The difficulty would be in making it serve a purpose; you might as well leave the window empty if you’re going to allow it to stop only the very first bullet it encounters in the round.
But the devs did make that choice at least once; the windows in arena_watchtower are all breakable. It kinda makes sense because arena maps are so fast-paced that the windows will quickly respawn once all the players do, and the control point is already so reinforced you certainly wouldn’t want those windows bulletproof. So it could serve something of an aesthetic purpose in other maps; put breakable windows in spots where you’d prefer there not be a window but the map design doesn’t encourage a glass-free wall opening. Then again, the fact that they never revisited the notion implies they might have found something wrong with it. Perhaps maintaining the in-game consistency of “glass=always unbreakable” is more important.