fix: Xcode 16 has broken the way we calculate the distance

[pbodsk]

Why?

I don't know...but they did 😉

What?

Apparently, the way we calculate how much to move for each "tick" in the CADisplayLink is broken.

Currently

We calculate a duration (a delta time since last render) and use that to calculate how much (position) and how fast (velocity) to use.

That duration is calculated like so:

let duration = displayLink.targetTimestamp - CACurrentMediaTime()

In the end of each "tick" we use this check:

if position < scale, velocity < scale

to determine if we should stop the animation or not.

But

The calculation displayLink.targetTimestamp - CACurrentMediaTime() has changed in Xcode 16, meaning that we can now get negative values from this calculation.

That again means that our velocity and position starts to act funny and we never end up in a positive check, meaning that our animation just continues forever.

We are not the only ones seeing this problem:

https://forums.developer.apple.com/forums/thread/762291

The Fix

Instead of subtracting CACurrentMediaTime we subtract displayLink.timestamp which seems to give us equally values to work with. Here is a piece from the documentation for CADisplayLink:

You calculate the expected amount of time your app has to render each frame by using targetTimestamp-timestamp. Use targetTimestamp-CACurrentMediaTime() to calculate the actual amount of time.

This seems to work and leaves us with similar results both in iOS 18 and pre iOS 18 so we'll go with that

Show me

Before	After
https://github.com/user-attachments/assets/37570e5b-c85d-457e-abb2-7f13b438c31b	https://github.com/user-attachments/assets/30f45ad9-90b2-4b8a-af09-0448405c69ad

[osanoj]

Nice work 👏