Scan a list

A collision can contain several contact points. PlayerMotor.UpdateGrounded scans them until one normal points up past the grounding threshold.

The problem

Using only the first contact can miss the floor when the player touches a corner. The motor must inspect each contact, but it can stop as soon as one proves the player is grounded.

When to reach for it

• A collection must be inspected one item at a time.
• Finding the first match is enough.
• Work can stop as soon as that match appears.

See it

Figure 1. The loop checks each contact normal and returns after the first grounding match.

Do it

1. Open PlayerMotor.UpdateGrounded in Graph View.

2. Read the for-loop controls: i starts at zero, continues while it is less than collision.contactCount, and increments once per pass.

3. Inside the loop, follow i into collision.GetContact(i), then read the contact’s normal.y value.

4. Follow the branch that compares normal.y with GroundNormalThreshold.

5. Follow the true path. It sets _grounded to true, then returns before another contact is read.

6. Follow the false path back to the loop. The next contact is checked until one passes or the collection is exhausted.

You should see

Every contact gets at most one visit, the first grounding match sets _grounded, and the early return avoids unnecessary checks.

Change one thing

Pretend the contact normals arrive as -0.2, 0.3, and 0.9. With GroundNormalThreshold at 0.5, trace the loop and stop where the method returns. Only three contacts are read, and _grounded becomes true on the last one.

What it writes

The current Platformer method is:

C#

What it writes

C#

private void UpdateGrounded(Collision2D collision)
{
    for (var i = 0; i < collision.contactCount; i++)
    {
        if (collision.GetContact(i).normal.y > GroundNormalThreshold)
        {
            _grounded = true;
            return;
        }
    }
}

The return ends the method immediately. If no contact passes the threshold, the loop completes without setting _grounded.

When it goes wrong

When it goes wrong

Symptom	Check	Fix
Only the first contact is checked.	Follow the loop condition and iterator back edge.	Keep GetContact inside the loop and feed it the current i value.
A wall contact marks the player grounded.	Read the comparison against GroundNormalThreshold.	Keep the upward-normal threshold on the true path before setting _grounded.
Contacts continue to be checked after ground is found.	Trace execution after the _grounded assignment.	Connect the return directly after setting _grounded.

Next

• Loops: read initializer, condition, iterator, and body.
• Return and throw: follow the early exit from the loop body.
• Get and set: follow the write to _grounded.