itch.io

Ah, yeah. I figured it was for the camera. In my head the two cases that are possible are the same as what you already mentioned: to either have the camera have collisions so that it stays within one side of the walls, or to set up better conditions for when the wall turns transparent.

For the first case, the camera would have collisions relative to walls  (basically the way the camera works in Minecraft if you play in 3rd person POV). The advantage here is that while the camera is following the player character (PC), a wall will never come between the PC and the camera. The only problem I can imagine with this is that if the player enters an area that's too narrow it always forces the camera to be close to the player which will make it hard to look around, but I don't think that's a problem with your game since it's made of nice open rooms and it might only happen if the player walks through doorways.

For the second case, you'll have to figure out what the conditions are for having a wall turn transparent. What I think you want is something that checks whether there's a wall between the PC and the camera, and if so to turn that related wall area transparent. Because I noticed that some walls still turn transparent even though they don't have to; e.g., I'll run into a wall in front of me but the camera is behind both the PC and the wall so I can still see clearly, but the wall turns transparent anyway.

If it's the second case, the way I would do it (don't completely trust me on this; I notoriously hard code stuff because I'm not good at optimising DX) is I would create a large invisible cylinder that stretches between the PC and the camera, and then I would code it so that if that cylinder overlapped a wall it would create a mask and subtract the texture of the intersecting parts. Essentially, the cylinder would cut a hole in the wall so the camera can look through and see the player. IMPORTANT to note that the masking only affects the texture itself and NOT the geometry. Because you want the collisions of the object to remain intact so the player doesn't use this effect to jump through holes in the wall. Essentially, it will look like a part of the wall isn't there, but in fact the whole wall is still there. 

Also, if you have the time to do so, you might want to look at alternatives to just straight up making a wall panel transparent. I know some make like a gradient of transparency so it's fully transparent/translucent in the middle but it gets more opaque radially outwards. I've seen others use like a combination translucent and dithered effect, but I think that one worked for those games because they were like  voxel/3D pixel type games. Just look at what you can find and see what works for you.