CABasicAnimation speed -- Keeping up with user input

Question

Update: It really was as simple as not animating the UI element when utilizing touches. It perfectly follows touches now with no lag.

I'm currently attempting to implement a UI feature by implementing a CALayer subclass inside of a UIView subclass. I receive touch events in the custom UIVIew's corresponding view controller, notify the UIView about the touches, which in turn notifies the CALayer in order to animate the UI elements drawn in the layer.

It all works, but I have noticed that when there is a big delta in movement (as in when quickly scrolling a finger), the CABasicAnimation lags behind. Ideally I want the animation to stay perfectly aligned with the user's finger.

I've come up with a hacky way of just setting the animation's speed arbitrarily high as in

anim.speed = 10.0f;

which essentially keeps up with the user's finger, but I feel that this is a total hack and not a shippable solution. Should I be artificially limiting how many touch events are processed in order to solve this problem? Is there some sort of calculation I should be doing for the speed/duration of the animation that I'm not aware of?

Thanks for any help with this!

Answer 1

During the continuous gesture, one shouldn’t animate movements, but rather just move directly to the gesture’s location. When the gesture finishes, if you want it to settle in some other position, then animate that final, post-gesture, destination. But don’t animate during the gesture itself.

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In rare cases, where rendering of a single frame is incredibly slow, there can still be perceived lagginess. Obviously, one should optimize the draw(_:) process so that it isn’t slow (or take a snapshot and animate the snapshot view rather than the complicated view). But during the gesture, you can also use “predictive touches,” where the OS estimates where user’s gesture is going to be in the future. For example, you can implement touchesMoved(_:with:) and then call predictedTouches(for:). By moving the view to the predicted touch location, it reduces perceived lagginess.