2D Platforming Physics With Raycasts: Jumping

Hello, faithful reader(s)!

It occurs to me that I didn't actually explain how I do the jumping in my system. It's simple, but there's a couple of nuances that should be discussed.

Basic Version

Jumping in Unity can be as simple as:

void Update (){
     if (grounded && Input.GetButtonDown("Jump"){
          velocity = new Vector2(velocity.x, impulse);
     }
}

This works, but there's a hidden mechanic in most of the platformers you play that you might not realise: you can actually press the jump button right before you land, and jump immediately as you hit the ground. If this feature is absent, your game will feel glitchy. The player expects this leeway. This means we're going to have to record when, not just whether,  the jump button is pressed.

Disclaimer: Unity has a function, Input.GetButtonDown(). I don't trust it - I find sometimes it just doesn't register. So I work around it with Input.GetButton, which returns true every frame the button is pressed.

Better version

My code looks something like this:

void Update (){
     bool input = Input.GetButton("Jump");
     if (input && !lastInput){
          jumpPressedTime = Time.time;
     }
     else if (!input){
          jumpPressedTime = 0;
     }

     if (grounded && Time.time - jumpPressedTime < jumpPressLeeway){
          velocity = new Vector2(velocity.x, impulse);
          jumpPressedTime = 0;
     }

     lastInput = input;
}

So a couple of things at work here. First, the time we pressed the jump button is recorded only if the previous frame, it wasn't pressed. Every frame we're grounded, we'll test the current time against the pressed jump time, to see if it's less than our jumpPressedLeeway variable (which is usually like 0.1). Then we jump if that's true (if we're grounded).

Setting the lastInput at the end is essential to check if this is the 'JumpDown' frame.

Disclaimer: I haven't tested this code. How fun! Check it, see if it works. Let me know what's wrong!

You can also add other conditions to the jump check. If you have a double jump, your condition may want to read:

if ((grounded || !hasDoubleJumped) && Time.time - jumpPressedTime < jumpPressedLeeway)

This way, grounded and not having double jumped will both satisfy the jump condition - but you'll also have to add:

     if (!grounded)
          hasDoubleJumped = true;

Then when you land, set it to false again.


That's it for now. Soon, I will go into doing slopes with this kind of system. I will also discuss jumping in a little more detail as it pertains to the system of checking downward for stuff. You'll see.

Thanks for reading!

Until next time: stay real, natural numbers.
-mysteriosum(the deranged hermit)