ID:1979060
 
(See the best response by D4RK3 54B3R.)
Does anyone know if there a way to make 1-way opacity or something similar to that?

What I'm trying to do is make a room where, if a player is inside, they cant see past the walls of the room but to anyone outside of the room, they can still see through the walls and inside.
Well...that's similar to what I want to do but not exactly.

Problem with using that is the wall on the opposite side of the room will still be opaque to people on the outside.

What I'm trying to do is make something like a 3x3 tile area where if you're standing in that area you cant see outside of it. But if you're standing outside of it, your vision isn't affected, you can see inside as well as see straight to the other side with none of the shadow blocks popping up.
Make the one-way opaque walls point in?
That wont work.

If a player is standing outside of the room, the wall on the far side from them will still be facing them and block light.

What I want to see is this.
http://i.imgur.com/eP5QyIl.png

Using the opacity in the demo will give me this...
http://i.imgur.com/GbQ8R3w.png
In response to IceFire2050
I'm not entirely sure how the demo is set up, but you'd probably have to create different objects depending on which way the opaqueness is.
One way I can see this working is to use screen objects instead. Add a scenary for the player who is affected (or a black background, whatever you want) to the client's screen. Then, on a layer above that, add the walls. To every other person in sight, don't add the scenary, just the walls
Best response
If you're not using invisibility for anything else, there's some hacky stuff with atom.invisibility that you could use.

Set everything to invisibility 1 by default and then set the mob's see_invisibility to 1 by default, and then set the see_invisibility to 0 when you go inside the area.