Unity 3D - Raycasts wont register in time if player has high enough velocity

Question

hope someone here smarter than me can figure out my mistake. I have a simple platformer game using raycasts to check if you’re standing on the ground. I tried colliders, but started using raycasts to be able to jump just before the player collides and thereby losing his x-velocity to friction, which would be a problem to how the game is supposed to be played.

That is exactly what happens. If you fall fast enough, then the x-velocity turns to 0 instantly instead of the player jumping just before collision and retaining his x-velocity.

It seems my raycasts do not check in time, or something else fails that I just cant figure out. Here’s what I have tried so far by reading other posts complaining about raycasts not registering, all to no different result:

• Turning on Continous collision detection in my players rigidbody instead of Discrete
• Putting the raycasts in FixedUpdate (made it worse)
• Putting my Movement script right after Default Time in the section Script Execution Order in Project Files

 public void Jump()
    {
        LayerMask ground = LayerMask.GetMask("Ground");

        Vector2 bottomCenter = new Vector2(transform.position.x, transform.position.y - transform.GetComponent<Renderer>().bounds.size.y / 2);
        Vector2 bottomLeftCornerPos = new Vector2(transform.position.x - transform.GetComponent<Renderer>().bounds.size.x / 2, transform.position.y - transform.GetComponent<Renderer>().bounds.size.y / 2);
        Vector2 bottomRightCornerPos = new Vector2(transform.position.x + transform.GetComponent<Renderer>().bounds.size.x / 2, transform.position.y - transform.GetComponent<Renderer>().bounds.size.y / 2);

        // Cast a ray straight down.
        RaycastHit2D down = Physics2D.Raycast(bottomCenter, Vector2.down, 1f, ground);
        RaycastHit2D downleft = Physics2D.Raycast(bottomLeftCornerPos, Vector2.down, 1f, ground);
        RaycastHit2D downright = Physics2D.Raycast(bottomRightCornerPos, Vector2.down, 1f, ground);

        // Determine the closest hit point
        RaycastHit2D hit = down.collider != null ? down : (downleft.collider != null ? downleft : downright);
        if (down.collider != null && (hit.collider == null || down.distance < hit.distance)) hit = down;
        if (downleft.collider != null && (hit.collider == null || downleft.distance < hit.distance)) hit = downleft;
        if (downright.collider != null && (hit.collider == null || downright.distance < hit.distance)) hit = downright;

        // If it hits something...
        if (hit.collider != null)
        {

            if (hit.distance >= 0.01 && hit.distance <= 0.1 && rb2d.velocityY <= 0)
            {

                rb2d.velocityY = jumpPower;
                comboExperiration = ComboExpireTime;
                comboCounter++;


                //Since we are not colliding with floor, send a message to Player Stats that we jumped on a floor
                if (hit.collider.gameObject.CompareTag("Floor"))
                {
                    GetComponent<PlayerStats>().CollisionByJump(hit.collider.gameObject);
                }

            }
        }
    }

Jump() gets called in inputManager script:

void Update()
    {

        if (playerInput.MovementMap.Jump.inProgress)
        {
            player.GetComponent<PlayerMovement>().Jump();
        }

Hope anyone here recognises this problem or can see my wrongings

Answer 1

Edit: I am changing my answer because my original assumption was not quite right. The problem is not the raycast origin piercing through the object. Though I was close in some sense.

How it works is this:

FixedUpdate
Update - no hit
Update - no hit
Update - no hit
FixedUpdate
Update - hit, distance 0.7
Update - hit, distance 0.7
Update - hit, distance 0.7
FixedUpdate
Update - hit, distance 0
Update - hit, distance 0
Update - hit, distance 0
FixedUpdate
Collision

• FixedUpdate - updates physics and moves the object, this is why it can't really pierce into the ground.
• Update - where raycasts are updated

So, it doesn't pierce through the object. Instead, when velocity is high enough, it stops exactly at 0 distance. Which is filtered out by this check:

hit.distance >= 0.01 

Can this be fixed by hit.distance >= 0 check? Only partially, the code will process a hit, but the collision will still be reported in next FixedUpdate.

So the options are:

• use prediction to avoid collision, basically what @Gerry Schmitz describes in the comment,
• use 0 distance, but ignore the collision when there's a hit right before it. Seems easier as it uses the same code, but could be tricky to synchronize, as hits are calculated in Update and collisions in FixedUpdate.