calculated animate duration

[yanshay]

I'm trying to scroll a list of items using animate.
Because the list of items could be short or long I need the animate time to be dependent on the preferred-height of the VerticalLayout, or the number of items.
I can't get the animate duration to get it's value from a calculated property or a direct calculation or even a property that I assign constant value to.
If I do either of these it behaves as if the duration is 0.

Is there a way to have the duration be calculated in any way and not hard coded in the code in advance?

[Vadoola]

I'm on mobile right now so my ability to test this is minimal. I grabbed an old slintpad link from a discussion I opened on animating paths and added a duration property to the animation. It seems to work fine:

That's an old version of slint, maybe copy and paste that code into the latest slintpad to see if its not a regression?

[yanshay]

Ok, so seems like in general it work, but in my case it doesn't. Here is a simplified example.

There are a few options there to uncomment:

animate y {
      duration: 2s; //<- always work 
       //duration: list.height / 200px * 5s; // <- works on my local machine slint live preview, not on slintpad
       // duration: list.preferred-height / 200px * 1s; // <- doesn't work anywhere
       // duration: top-items.length * 1s; // <- crash the slint LSP/Live-preview, slintpad(stop working)
       easing: ease-in-out;
}

The interesting thing is (list referred to below is is a VerticalLayout)

1. The constant work.
2. The duration based on list.height - work on my local slint-preview, but doesn't in slintpad.
3. The duration based on list.preferred-height - doesn't work on neither slint-preview nor slintpad
4. The duration base on a property which is an array of string, length: crashed my Lsp / Local SlintPreview, and also hangs SlintPad.

[Vadoola]

I'm still on mobile so can't dig too deep, what if you move the duration calculation into a function? Does that alter how it functions or crashes?

I do wonder if this needs to be made a bug report.

[yanshay]

moving the duration calculation into a function doesn't change.

I played a bit more and the behavior around this is even more strange.

In this example which is similar to previous one, I managed to get the preferred-width to influence by trial and error.
However:

1. To make it animate, I had to add a small rectangle there. without it, it jumps as if duration is zero.
2. Any minor change to the rectangle height has large influence on the duration calculation even though the rectangle is very small compared to the preferred-height
3. The duration time that takes place is very different from the calculation - I added the calculation information on top of the display so it can be seen. it should be 98 sec, while in practice it's only a few seconds.

Seems to me like something I'm doing there generates several bugs of all sorts.

[Vadoola]

Hmm yeah, I'm wondering if this needs to be made into a bug report. There could be multiple things coming into play here.