Re: [css-transitions] Proposal and RFC: spring() timing function

> 
> (Alternate syntax: use units for these, like `spring(2mass
> 5velocity)`. Stronger connection between value and type, but also
> maybe weird? Unsure.)

"mass" and "velocity" aren't units, they are types of units. This would be like writing "8length" instead of "8px".

Please don't make physicists cry.

> 
> (Second alternate syntax: finally invent "named arguments" for real,
> like some people have been agitating for for a while.  `spring(mass:
> 2; velocity: 5;)`?  To be less weird we'd have then go and backport
> this to other functions. Probably a decent idea? Need to noodle on
> syntax more, look at several different functions that use syntax
> differently.

That's a more appealing syntax and makes it easier to figure out defaults.
> 
> 
>> We could pick another formula that is more amenable to duration-based
>> springs.
>> 
>> However, there is some criticism against coding an animation like this
>> purely on duration:
>> https://medium.com/@flyosity/your-spring-animations-are-bad-and-it-s-probably-apple-s-fault-784932e51733 <https://medium.com/@flyosity/your-spring-animations-are-bad-and-it-s-probably-apple-s-fault-784932e51733>
> 
> That criticism is geared towards a bad API design that required you to
> specify a *technically redundant* duration, and if you didn't specify
> what the algo would have "naturally" provided you get an
> unnatural-looking result.

My read is that it actually solves the spring equation in reverse and computes a stiffness and mass for the given duration. There is no stiffness or mass provided to the API, just damping (as a ratio, presumably relative to stiffness or something) and initial velocity. So the duration is not redundant.

I think the reason the spring examples using the API look bad is that authors are likely to severely underestimate the duration required for a comfortable looking bounce, thus resulting in springs with crazy high stiffness which look awkward even though they are technically correct.

Regards,
Maciej