Unintended Behaviour: Holding jump whilst on ladder keeps jump speed at max

[AtomicCrocStudios]

Describe the bug

I feel like this unintended behaviour which can be replicated in the platformer example or the attached file (has default keys disabled and a debug showing jump speed).

When on a ladder, pressing up and jump at the same time you zoom to the top of the ladder maintaining maximum jump speed as if you have infinite double jumps.

I think that whilst on the ladder, jumping should work like normal however when at the apex of the jump (before the player starts falling) their jump speed is set to 0 so they stop on the ladder (if pressing up and jump are still active, it starts jumping again)
See the jumping platforms next to the ladder as an example.

https://drive.google.com/file/d/1ulqCosy7C1MiK2xbJhPJ862qlYcpctAj/view?usp=sharing

To Reproduce

Steps to reproduce the behavior:

1. Stand at ladder
2. Press UP + Jump
3. Reach the stars!

Other details

• Tried in Beta 103, 102 and 101
• Windows 10

[4ian]

It's true that it's a problem right now! I'll think about how to improve this.

[arthuro555]

One possibility would be in the default controls to disallow climbing the ladder while pressing the jump key/while the momentum is going up

[4ian]

disallow climbing the ladder while pressing the jump key

It's possible this way, but then a player could spam the jump key and the ladder key.

while the momenting is going up

I was also thinking about this, but this means that if you try to reach a ladder that is above you by jumping on it, you might not be able to grab it.

Note that these two things can already be done manually with events :) (disable default controls, and use the actions to simulate key press, only allowing a jump if you're also not pressing the button to climb a ladder).

We could maybe add a "time before being able to grab again a ladder after leaving one":

• this would allow to avoid the repeated jump/climb, because you could certainly jump from a ladder, but you would have to wait something like ~0.3 seconds before being able to grab it again and jump again.
• if we add a button to release a ladder, it would avoid to repeatedly release/climb in the same way (like in the first Tomb Raider where you could climb down by releasing a ladder/grabbing/releasing/grabbing).
• you could still set this to 0 seconds if you want this repeatedly jump/grab or release/grab to work (or you could set it to a very short time for nervous platformers, or a longer time to be sure to avoid these unrealistic behavior).

[rahljoshi]

Can I try to work on it??

[4ian]

Sure feel free to go ahead! There are unit tests for the behavior that I recommend looking at.

[rahljoshi]

Ok! & thanks for allowing me :)

[85ayush]

I would love to work on this issue, I am new to open source contribution, can you please guide me?

[D8H]

I think the solution given by Arthuro should work.

Maybe the player should be allowed to grab a ladder when he's jumping only:

• if he's on the descending phase of the jump
• or if he left the ladder at some point (so the player can still jump from one ladder to another horizontally)

So, if you jump and grab the same ladder, it will act as if you're going from one jumptrough to another. I think it will feel natural.

I made a unit test on this.

[4ian]

if he's on the descending phase of the jump

That could be frustrating in a game where you want to grab a ladder, but your character does not because the game decided that you're jumping and not falling (and so you end up colliding with an enemy and dying. Or you end up falling a bit, touching the lava below the ladder and dying).

I've not checked all platformer games, but are there examples restricting ladder grabbing to when we start to "fall"?

or if he left the ladder at some point (so the player can still jump from one ladder to another horizontally)

Yup that's important to keep.

I still think this could be solved by a "time before grabbing a ladder again after leaving a ladder" (knowing this time is reset if touching the floor) as I wrote in #2236 (comment) as it avoids most problem and still give you the ability to grab again the same ladder.

Feel free to argue for the other solution though :)

[D8H]

To give players more control, maybe he should be able to grab the ladder with up and down keys. So, it's always possible to grab the ladder with an action that is opposed to the movement :

• can grab with up key, if going down or if the speed on y < ladder movement speed
• can grab with down, if going up or the if speed on y < ladder movement speed

(and of course, no constraints the 1rst time)

Indeed, there is no reason for the player to grap the ladder with up if he's already going up faster jumping. If a player want to avoid an obstacle over him, I think it's a reflex to press down.

Holding up + jump, the speed will be between ladder maxium speed and jumping maximum speed.

[4ian]

I think you might be able to do this with events, but by default I'm not convinced this is the default behavior we should go for: it seems to complicate a big things - unclear for a first time player why there would be two buttons? Or you should be able then to use both buttons when you're on top of a ladder - because it's vertical.

But in any case - this won't solve the initial issue of loop jumping while on a ladder right?

[D8H]

There are already 2 buttons to move up and down on the ladder but only one makes the grab. But I think you're right it may not fix the issue because it will only make the loop less frequent, like a timer would. I don't like the idea of using a timer because the other settings will have a side effect on the fix and it may be hard to setup correctly.

The jump has kind of a bug at the first step: it doesn't apply gravity. When looping, this first step is repeated. I think it works like this to avoid the player to be stuck in the floor. So, I guess this behavior can safely be disable when the jump happens on a ladder. There will be no perceptible change for the player and it could already reduce the propulsion to something like a continuous jump sustain.
This is easy to do with the big refactor, I will try it tonight.

[4ian]

The jump has kind of a bug at the first step: it doesn't apply gravity

Are you sure you're not confusing this with the feature "jump sustain time" which allow to change the jump height according to how long you keep pressing the jump button:

GDevelop/Extensions/PlatformBehavior/platformerobjectruntimebehavior.ts

Lines 462 to 467 in e9e86e3

	const sustainJumpSpeed =
	this._jumpKeyHeldSinceJumpStart &&
	this._timeSinceCurrentJumpStart < this._jumpSustainTime;
	if (!sustainJumpSpeed) {
	this._currentJumpSpeed -= this._gravity * timeDelta;
	}

This is easy to do with the big refactor, I will try it tonight.

The big refactor is already fairly big, I would strongly strongly recommend to not add any feature at all. Let's concentrate on getting the refactor done: a safe refactoring with all the nice tests you've been adding :) Otherwise I'm afraid bugs will slip because it's hard to both review a refactoring and a new feature at the same time.
EDIT: of course this can always be in a PR on top of the refactoring ;) I'm just concerned about the stability of the whole thing if we start doing changes at the same time as we're moving to a new pattern.