No, sorry, if there is a one pixel gap and the player presses alt they can slip through it. There is a suggestion to have transparent walls in the suggestion forum. You can do a solid wall and then make a token that has vision and is controlled by all players set on the other side of the wall as a work around. just make your porticullis thick and draw a very thin D.L. line through it and place a camera on the other side, the camera can be any token, I like to use something innocuous, like a scrap of crumpled paper. BTW, I also use scraps of paper in the street for city scenes with thief skills attached to them, they just come up missing something if it is successful, if the roll fails, I place a "thief" token on the VTT for them to interact with.