Real-Time Portal in Unity

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 After struggling (and finally succeeding) to get my first-person player working in Unity — thanks to some Collider wrangling and ChatGPT saving the day — I was ready for the real challenge: the portal system.

I mean, how hard could it be?

Well… harder than I thought, but also kind of awesome once it started working.

The Secret Sauce: RenderTextures + Cameras

The first thing I learned from the YouTube tutorial I mentioned last time
This one — was that the magic behind a portal is basically just a camera + a RenderTexture.

Here’s how it works (in student terms):

  1. You place a camera in the destination scene (or behind the portal).

  2. That camera’s view gets rendered onto a texture.

  3. You slap that texture onto the surface of the portal in your current scene.

  4. Boom — it looks like you're peeking into another world. 

It sounds simple, but it took a while to set it all up properly.

Building the Portal Frame (Again, Thanks C4D)

I already had my portal model from Cinema 4D, so I imported it and used it as the frame. Behind it, I placed a quad (flat plane) that would act as the screen showing the RenderTexture.

Then I:

  • Created a new RenderTexture asset in Unity.

  • Created a new Camera, pointed it where I wanted the portal to lead.

  • Assigned the RenderTexture to that camera.

  • Applied the RenderTexture to the material on the quad.

Suddenly — I could see another part of my scene through the portal 🤯

A Bit More Magic: Camera Sync

Of course, just showing the other scene wasn’t enough. The portal had to move dynamically with my player — so when I looked left or right, the view through the portal updated too.

That part was trickier.

I needed to:

  • Sync the "destination camera" (the one rendering the portal view) with the player's head movement.

  • Mirror the rotation, position, and even adjust for offset depending on where the portal is.

The YouTube guy covered this in detail, so I followed his steps. But I still ran into a few hiccups — mostly because I forgot to flip the Y rotation and align the camera’s local position properly.

More Bugs, More ChatGPT, More Fixes

Not gonna lie, the portal was super buggy at first:

  • Sometimes the RenderTexture would turn black.

  • Other times the camera would clip weirdly.

  • Occasionally I’d walk through the portal and… fall into the void 

Each time I hit a wall, I either:

  • Went back and rewatched the video for the 10th time.

  • Asked ChatGPT how to fix RenderTexture errors or camera clipping.

It took a few hours of tweaking, but eventually it all started to feel super smooth. I could walk right up to the portal, rotate the camera, and see the other side update in real-time like in the actual Portal game.

Final Result: It Works!

I now have a working camera-following shader portal, and the scene transitions look so cool. It’s not perfect — I still need to implement teleportation when stepping through, but visually? 10/10 satisfying.

I didn’t expect to get this far as a Unity beginner, but combining what I know from C4D with some research and AI help made it surprisingly possible.

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