RFR: JDK-8306990: The guarantees given by Region's floor and ceiling functions should work for larger values [v2]

[Andy Goryachev]

On Thu, 27 Apr 2023 19:15:56 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> Region has floor and ceiling functions that ensure that calling them twice in a row will yield the same result:
>> 
>>      ceil(x) = ceil(ceil(x))
>> 
>> However, due to use of a constant `EPSILON` which is added/subtracted before doing the rounding, this only works for small numbers (in the range of 0-50 approximately).  For larger values and scales, rounding errors can easily occur.  This is visible as artifacts on screen where controls are a pixel wider than they should be.
>> 
>> The use of the `EPSILON` constant is incorrect, as its value depends on the magnitude of the value in question (as magnitude increases, the fractional precision decreases).
>> 
>> The Math class offers the function `ulp` that should be used here.  It represents the smallest possible change in value for a given double.
>> 
>> Extending the existing test case `snappingASnappedValueGivesTheSameValueTest` to use larger magnitude numbers exposes the problems.
>
> John Hendrikx has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - Print seed if test fails
>  - Merge branch 'master' into feature/ceil-fix
>  - Fix Region ceil/floor function guarantees to be more accurate

> I'm not able to reproduce it.

I am trying to run the code after a clean build, and can't - the MonkeyTester freezes going in an infinite loop in HBox.growOrShrinkAreaWidths() on line 517 when launching to an HBox page.

And when launching to a different page, the layout all gets messed up:

![Screenshot 2023-05-01 132041](https://user-images.githubusercontent.com/107069028/235538707-2ac949d7-6257-4a66-8847-3dc73a5f1e64.png)

also, looks like it's entering infinite loop when moving the window from primary monitor on windows 11 (scale=100%) to the secondary (scale=175%)

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PR Comment: https://git.openjdk.org/jfx/pull/1118#issuecomment-1531657744