How passable (one-way) platforms work in game development! 

another way: check if y speed is upwards or downwards

This video is brought to you by "Solving a computational problem by throwing more processing power at it".

You can avoid all the constant checks by checking the collision normal when colliding. The normal will tell you which direction your hitting the platform from. Can just ignore if hitting from bottom 🤟

Nice video! Unsolicited fun fact to boost the _algorithm_: In the original Super Mario Bros, the game checks if Mario is landing on an enemy (good) or being landed on (bad) just by checking Mario's vertical velocity component. Thus, you can squash a goomba from below if it lands on Mario while he is falling slower than it.

Insane amount of checks per minute… just get the normal of the object or set the normal to a directional vector

What I did on my one-way platforms was make two hitboxes: one for the bottom and one for the top (in the case of your grated platform, it would be the 2 highest pixels). The bottom hitbox lets anything pass through it, and is just there as a sensor: the higher hitbox would have no collision with anything touching the lower one, but would with anything not touching it.

A trigger collider below the actual collider: I'm about to end this man's whole career

In Unity you can add a platform effector 2d and it makes it a one way platform automatically, just make sure to check "used by effector" on the collider you are wanting to change.

In godot I just check "one way collision" lol

You could also have a check on collision to see if the player is below the position of the platform, and ignore it if it is

This works fine if it’s just a single player and simple npcs. However this falls apart if you have add multiplayer or any traversal ai behavior. Also the colliders will spend every frame checking the player’s y position. I’d probably tie the collider flag (i.e. the character’s collision layer) to the entity that is jumping based on it’s movement vector. If a player or entity is moving in the positive y direction, it should not collide with platform. On the way down if it moves in the negative y or is at 0 delta it should check if its collider overlaps the platform. If not then switch the collision flag back. The neat thing with this is you can also make the player “hop down” from the platform by toggling the collider flag based on user input.

Unity has a component called Platform Effector2d that you can attach to your colliders. It ignores collisions from specific directions if you enable the one-way option.

This sounds perhaps computationally heavy? But a nice solution. I always just checked The direction of vertical velocity.

Really cool. The movement and animations of that bird is nice as well.

The velocity check or using the normal is probably the most efficient solution here, but another thing you could do is have another bigger collision box around the platform that checks if the bird is above or below it. So it only checks if the bird is near it, instead of all of the time

This actually helps, thank you

You should make a follow up demonstrating how to jump down through it. Pretty easy but interesting

The way I had learnt to solve this is to create a variable to check if you're colliding with the platform or not and if you are, check the y-position until you're above the platform to allow you to pass through or to stop you. I also used this to allow the player to fall through the platform if they're holding down on it. This was technically intended for allowing sloped platforms but I never used any because I preferred blocky level design.

I didn't something similar in 3D for a end of studies project. Rather than check constantly, which doesn't work at scale, I only checked on collision, and then changed the behavior right away. Because I was on Unity and due to how their collision system is built, I just kept it "on" at all times and disabled it if the collision met my criteria (the call was the first step in handling the collision, and changing it to a trigger simply changed the behavior later in the call chain). I could then just enable it back when the character exited the box. One benefit of this approach was that it was not expensive and was still consistent. One drawback is that it was dependent on engine behavior, we couldn't know if another version of unity could break it. But in the context of our project, we could take the risk, as upgrading our unity version wasn't a current or future requirement.

It's more resource efficient to shift the logic from the static platforms to the moving entities passing torugh. Implement a collision check and snap entities above the tile if they try to pass trough them from above. It also enables more than just one entity to do the same simultaneously as the platforms keep their collision state the same at all times.

This lil birb is so cute!

Godot: I don't have such weaknesses

Located a bug: if you have an enemy that can jump, they will bonk against any platform lower than the player’s height. Jumping enemies cannot reach the player from below if they are standing on a one way platform

I think it would be better if each entity's script checked if it should collide with platform depending on the Y position, So that the platform collider is always active but player and enemies ignore it if their position is lower. This way both player and enemies could move through the platform and collide with it from above at any time

Should make it more dynamic and any sprite that is below it ignores the collision, rather than changing the platform can't the interaction between the spirits and the platform

I had never thought of doing it this way. Pretty cool.

Very helpful my guy!

for my games I use the method of If Yspeed > 0 : it will be traversable and if Yspeed

This might be a dumb question, but isn't this potentially a major performance issue? Since every collision is checking the player position at all times?

Immediately went into the comments as soon as I heard "platforms constantly checking if character is above or not"

In my games I just check if the y momentum is greater than 0 then it doesn’t collide.

Cool! I love learning about games

Yes! This is exactly what I'm looking for to create multiple layers for players to go in between like in SMB3! It's my favorite feature of that game!

love me some "always checking" platforms that totally scale with the size of the project.

I made a type of terrain It is intangible if your movement is upward or if you are inside it, if you stay at the same height or if you move down, the platform is solid. Additionally I made it so that if I pressed jump while crouching my character would check the pixel right below him, if it was this terrain then I would move my character down one pixel, this way I could also go down the platform whenever I wanted. Although in my project it was my character who did the terrain checks, not the terrain.

This just gave me an idea for a simple game. Thank you!

Gosh I Was thinking about the mechanism behind this thanks a lot

Imagine doing it this way but for multiplayer. Ya u gonna get alot of bugs. But this is perfect for a singleplayer

2 things: One - I really like how you explain how it works (fundamenrally atleast) instead of just giving tutorials with pre-made assets, learning how to demystify black box game logic is a huge part of advanced game dev and I love it Two - as far as your solution goes, I won't say its performance problematic unlike other people, I think it's just fine for the scope of the project. But I would like to suggest that a more individual approach that focuses on general game objects instead of just the player would boost level and enemy design ability since it would allow enemy AI to take advantage of the game mechanic which is kinda hard but super worth it

Each object checking your height means a lot of computing. You could have the player check when it's colliding with the platform wether it's above or not. You would only need to check for one node (player) only once, at collide event

this is helpful! thank you!

Always wondered how they did that. Thanks

Yo this is helpful, thanks man

could just make a custom collider script for those platforms that adds a check on collision enter to see whether it was the player that collided and, if so, whether they are above or below the platform. Cuts down heavily on checks per minute and should still provide exactly the same functionality.

This was more helpful then you can imagine

Thank you, brother

This'll definitely help. Making a metroidvania, and if you want to know how many of these are in one, play through one and take a drink for every new one you see.

I made different collision layers, one collier on the head that doesn’t collide with one-way platforms while body and feet do. when head overlaps with one-way platforms it changes the body and feet colliders to a “head” temporarily and when they exit it (either from jumping over it or falling below it they change back. This leaves less processing power (I think, since it only has to check colliders which it does anyway and not constantly check the Y axis of the player for each platform) and you can add this to enemies so they can jump through too! For this the platform needs to be thinner though, otherwise falling through the edges gets a bit wonky Another thing is that landing on a platform with your mid-body makes it shake but that’s fixable with side of body colliders that stops positive or negative horizontal movement and in this case because it’s a one-way disables it like the head All in all, instead of checking constantly it only checks when it collies followed by a bunch of if statements to determine what to do Again, I don’t know if this is better for the cpu but I believe so

You could instead add a collider that sits under the other collider. If player hits the bottom collider make the platform passable otherwise do not.

Amazing man

That's trippy, much like the earlier contra games

another cool frsture you should include is holding down and pressing jump to fall through the platform

For new Devs, it's best practices to eliminate unnecessary checks especially every frame all the time. In this case, U can use a proximity hitbox to trigger the check. Or Trigger check on every frame for X time when player jumps. Or when not grounded. Or the moment Y changes.

However if you want this to work for multiplayer, you can instead use a Y speed check to see if the targeted plater is moving up or down

Im just thinking of the place sound effect in mario maker, "semi-solid platform"

Instructions unclear: birb has been stuck when i came from the side

butter building my beloved

eyy this is a case where it makes sense to have the origin of the player at the bottom of their feet, but you of course can also do it with an empty, if say you wanted the player sprite to rotate from the middle and not from the bottom

If you have a lot of these checking every one constantly could be bad for frames and unoptimised. You could add an area where these get checked, so its not slowing performance

This is clearly a naive way to do it but I really like these reels where you explain this basic things on gamedev by example, keep doing this plz

Very Dreamland esque music ^_^

I have another solution that doesn't involve platforms checking on every frame Instead of using a box shaped collider, use a plane or a quad as a collider. Planes and Quads by default are one sided objects, being the front face the one with the collision, so if the player goes through it from below, it would ignore it until the player stands on top

Amazing video

I like the bird animation.

This could become quite expensive. The best ways to do this is to disable player collisions when jump is active OR check if the player's directional heading is up, if so we disable the collision also.

This is so cool

Ok, now i want to play your game.

It was helpful thanks

See, when I tried this way back when for a high school class, I tried solving it by using the motion that you can have upward movement through it, but not downward. The flaw with that design choice is that a player or entity can be partway through a platform like this, which can result in clip-based glitches. By having the platform be in a different state depending on position of the entity it effects, this problem is entirely avoided. This is a really helpful solution to view the problem with!

I remember going from Super Mario Bros. to SMB2 and this was a big effing deal! Also, top down games having 8 directions instead of just 4. Kids these days will never know how mind-blowing these minor technological improvements were.

Making Yandere dev proud.

I literally spent an hour trying to figure it out and then I opened my phone to take a rest and this video showed up

this probably depends on how much control you have over your platformer physics, but I'd probably just remove the side wall collisions entirely just in case

Run the check during collision, dont run it constantly for all platforms

Pet peeve: no down jump on platforms in certain games.

Now i'm imagining a system where just the player shoots out a little "jump bullet" whenever you press the jump button, which tries to collide with an object and, if it does, reads information about the object's position and context, and then tells the player how to jump

I've read how to make one way platforms and it didn't exactly click fully what I was doing until just now, thanks a lot

Mario land music is such a good choice 😊

Holy crap man thanks. I'm working on a platformer right now and was stuck on just that issue. I thought I could just go around platforms, but the level design is making that difficult. Thanks again.

Nice Kirby music.

Meanwhile Godot laughing at you

I'd probably be more efficient to disable collisions if the velocity of the player is upwards, that way you don't have to perform as many checks

Thanks so much

First thing i programmed was sth like this in BlueJ with boxes and a ball, i didn't even know you could call those hitboxes XD Really cool btw

I will (probably) never use this information but that's super cool anyway lol.

I would add an extra trigger collider below the platform to check if the player is in there and while it is, remove the collision of the platform

Thanks! Do you check the lowest point of bird and highest point of platform?

Well if there ever is an enemy capable of jumping to chase you more effectively it could also fall through a platform intentionally (maybe only after the player touches the ground) as a way to keep chasing or to kill/get rid of the enemy if something related is below

You could also achieve this by giving the bounding box a normal vector to compare to the player's velocity during collision checks.

Liked and subbed

If you're watching the video and stuck on how to implement it: Set the collision to disable when the *bottom* of the player's hitbox Y-level is below the *top* of platform's hitbox Y-level

In unity you can just use a platform effector and configure it to work this way, it can even include a falling effect where the player can go through the platform downwards jumping and pressing down button

I was coding a game for school and I accidentally made directional platforms. I don't know how, but it happened.

For anyone using Unity concerned about efficiency, this is a perfectly valid solution, and is more efficient than using a PlatformEffector (unless you want some of the extra bells and whistles PlatformEffector provides). If you want, you could also split the collider in 2, and have one be a trigger that disables the other one, which is about on par with this CPU usage wise. Most of the complaints about efficiency assume your engine lets you intercept the collision and choose to ignore it before the effects are applied, which Unity doesn't seem to allow, at least in what I've found.

this is one of the example that 3D movement played in 2D world.

Interesting way to solve it, wasn't the first that came to mind.

I feel like watching this I also lerned how clipping works.

in my most recent WIP game, i wanted to make oneways in different directions, so instead of making four objects (onewayUp, onewayDown, etc), i just made one that does trig to check the players distance in relation to its angle and face. sounds complicated, but it was simple enough, and had the added benefit of working in ALL 360 degrees

I think this might be unoptomized, but I don't have enough programming experience to offer an alternative

Back in dev school I was doing a 2d game in ue4. The solution I found was to check if the character vertical velocity was positive. If it was then it would ignore collision, but if was negative or equal to 0 then it would block collisions. Jenky but it worked :D