Roblox portal gun script physics are easily one of the most frustrating yet rewarding things you can try to tackle as a developer on the platform. If you've ever played Valve's Portal, you know the drill: "Speedy thing goes in, speedy thing comes out." It sounds simple on paper, but when you're staring at a blank script in Roblox Studio, trying to figure out how to translate a player's momentum through a 3D coordinate system without clipping them through the floor, things get complicated fast.
We aren't just talking about making two parts and teleporting a player between them. Any beginner can write a Touched event that sets a Character's CFrame. No, the real magic—the stuff that makes a game feel professional—is in the way the physics engine handles that transition. It's about conservation of momentum, relative orientation, and making sure the transition is so seamless that the player doesn't even feel the "teleport."
The Core Logic of Momentum
When we talk about roblox portal gun script physics, the first thing we have to master is velocity. In Roblox, a Part or a Character has an AssemblyLinearVelocity. This is a Vector3 value that tells the engine exactly how fast an object is moving and in what direction.
If you just teleport a player from Portal A to Portal B using a simple CFrame change, the engine might keep their world-space velocity. Imagine you're running North at 50 studs per second into a portal on a North-facing wall. If the exit portal is on the floor, you should be launched upward. But if you haven't handled the physics script correctly, you'll still be moving North, which means you'll just awkwardly slide across the floor the moment you exit.
To fix this, you have to do some vector math. You need to take the player's velocity relative to the entry portal's face and re-apply it relative to the exit portal's face. It's like telling the engine, "Take whatever speed I had going into this surface and make it the speed I have coming out of that surface."
The "CFrame" Nightmare
You can't talk about physics in Roblox without talking about CFrames. For a portal gun script to work, the exit CFrame needs to be perfectly calculated. If you're even a tiny bit off, the player will get stuck in the wall or, worse, get flung into the "null zone" because their Hitbox overlapped with the portal's frame.
The trick is using CFrame:ToObjectSpace() and CFrame:ToWorldSpace(). When a player hits the entry portal, you calculate their position relative to that portal. Then, you apply that relative position to the exit portal. This ensures that if you enter the left side of Portal A, you actually come out of the left side of Portal B. If you skip this step, the physics will feel "off" because the player will always snap to the exact center of the exit portal, which kills the immersion.
Handling the Raycast and Surface Detection
Before the physics even come into play, your roblox portal gun script physics rely on a solid raycasting system. You need to know exactly where the "bullet" hits and, more importantly, the Normal of that surface.
The Normal is basically a vector that points straight out from the surface. If you shoot a flat wall, the Normal points at you. If you shoot a slanted roof, the Normal points up and out at an angle. Your script needs this Normal to orient the portal correctly. If the portal isn't perfectly flush with the wall, the physics engine will have a stroke when the player tries to pass through. You'll end up with players bouncing off the edges of the portal because the collision boxes are fighting each other.
Pro tip: Use RaycastParams to make sure your portal gun ignores the player's own character and any existing portals. There's nothing worse than a portal gun that keeps hitting the portal you just placed.
The Seamless Transition (The "Magic" Trick)
One of the biggest hurdles in roblox portal gun script physics is the actual moment of passing through. Roblox doesn't naturally support "non-Euclidean" spaces. You can't actually see through a hole into another part of the map without some serious trickery.
While some high-end devs use ViewportFrames to create the illusion of looking through the portal, the physics side is handled by disabling collisions momentarily or using CanQuery. A common trick is to create a small "hole" in the wall using negative parts or by simply making the wall the portal is on non-collidable for the player while they are within a certain distance.
However, if you want to keep it simple, focus on the "push." When the player is halfway through, you need to make sure the physics engine is pulling them toward the exit portal while simultaneously ignoring the collision of the entrance wall. It's a delicate balancing act.
Dealing with Gravity and Falling
Let's talk about the infinite loop. You know the one—putting one portal on the ceiling and one on the floor directly below it. This is the ultimate test for your roblox portal gun script physics.
In a standard Roblox environment, gravity is a constant acceleration downward. As the player falls, their AssemblyLinearVelocity increases. Your script needs to be able to handle these rapidly increasing values. If your script has a "cool down" or a "debounce" that is too long, the player will fall through the floor portal and hit the ground before the script realizes it needs to teleport them again.
You also have to consider the "up" vector. If you fall into a floor portal and come out of a wall portal, your "down" is still down (toward the center of the Earth), but your momentum is now horizontal. If you don't transition that velocity correctly, the player will feel a weird "jolt" as Roblox's default gravity tries to override the momentum you just gave them.
Common Pitfalls and How to Avoid Them
I've seen a lot of people try to build these scripts, and they usually run into the same three problems:
- Network Ownership: If the server is trying to calculate the physics for a player moving at high speeds through portals, it's going to lag. It's almost always better to handle the actual CFrame teleportation and velocity math on the Client (via a LocalScript) and then inform the server. This makes the movement feel buttery smooth for the player.
- Orientation Snapping: If your exit portal is upside down, the player should come out upside down. If you don't account for the rotation of the exit CFrame, the player will instantly "snap" to an upright position, which looks glitchy and can actually cause the physics engine to trip out and launch the player into space.
- The "Stuck" Bug: This happens when the player's velocity isn't high enough to clear the exit portal's collision box. They end up oscillating between the two portals forever or getting wedged in the geometry. Always add a tiny "offset" to the exit position so the player is placed an inch or two in front of the exit portal.
Optimization for Low-End Devices
Not everyone playing your game is on a high-end gaming rig. When you're running complex roblox portal gun script physics, you're asking the CPU to do a lot of math very quickly. Raycasting every frame, calculating CFrame offsets, and monitoring velocity can add up.
To keep things optimized, only run the "detection" logic when the player is actually near a portal. There's no reason to calculate momentum conservation if the player is on the other side of the map. Using Magnitude checks to sleep or wake your portal logic can save a ton of frame time.
Final Thoughts
Building a functional portal system is like a rite of passage for Roblox scripters. It forces you to actually learn how the engine handles 3D space, rather than just relying on the built-in physics behaviors.
It's going to be frustrating. You're going to spend three hours wondering why your player keeps dying the second they touch the orange portal, only to realize you forgot to convert a Vector from Local to World space. But honestly? Once you get that first successful infinite loop going, and you see your character flying through the air with perfectly conserved momentum, it's all worth it.
Just remember: keep your math clean, watch your CFrames, and don't let the gravity vector win. Happy scripting!