Ok, first off, here is the original portal from Half-Life 2:
As you can see, it is also a type of monitor, because it is producing an image of quite a few towers, as seen in the picture above.
The towers are lined up outside the map, and have a "point_camera" entity staring at them.
For now we will use a couple of oildrums for our portals image.
First of all, make sure you have made a little seperate room for the barrels to lay in, and also for the camera.
Or, you could have your camera in the same room as the portal, I am making my camera in a seperate little room for this tutorial.
When you are making the spot that you want your camera to look at, be sure to add some props & models for the camera to look at.
When you have finished making the spot for your camera, scroll down in the "Entities" list until you find "point_camera" Then insert the entity into your map, and then position it to the spot that you want it to look at. Also remember to rotate the camera on the X/Y/Z axis until you are happy with where your camera is looking.
Then, when you are done, hit Alt + Enter while having the point_camera selected, and press on “Name” then, type in “cameraportal” and press Ok.
Here is my camera spot:
Once you have set the name of the camera, time to prepare the spot where your portal is going to go, make sure you have a big amount of space in your map for your portal.
Ok, once you are happy with your portal spot, look in the “Entities” list for “prop_dynamic” then, once you have found it hit Alt + Enter and press on “Name”, and type in “portal” then, press on “World Model” and browse for models/Effects/portalrift.mdl
Once you have found it, hit Ok, and then position it wherever you want.
Then, look in the “Entities” list for “info_camera_link”, and then position it wherever you want, it doesn’t matter where it is but it is recommended to put it near or next to the portal model, so you can find it easily.
Once you have done that, hit Alt + Enter with the “info_camera_link” selected, and where it says “Entity Whose Material Uses” (sorry, I cant read the rest, it goes off the frame) and then once you have pressed on it, go to the little drop-down menu, then locate and press “portal”, and hit Apply.
Then, press on “Camera Name”, and look for “cameraportal”, then hit Ok.
Then, once you have done that, it’s done!
Have fun messing around with huge portals