RFR: 8364049: ToolBar shows overflow menu with fractional scale

[Kevin Rushforth]

On Fri, 25 Jul 2025 17:13:30 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

> This is a very localized fix for the issue described in https://bugs.openjdk.org/browse/JDK-8364049 which resulted from comparing snapped and non-snapped values.  The issue seems to happen only with fractional scale, that is, on Windows at 125%, 150%, 175% etc. scales.
> 
> ---
> 
> While looking at the `ToolBarSkin` code, I noticed a general pattern related to snapping, that might cause similar issues in the tool bar skin and elsewhere.  Here is an example in `ToolBarSkin::computePrefWidth()` in L411:
> 
> 
>         if (toolbar.getOrientation() == Orientation.HORIZONTAL) {
>             for (Node node : toolbar.getItems()) {
>                 if (!node.isManaged()) continue;
>                 prefWidth += snapSizeX(node.prefWidth(-1)) + getSpacing();
>             }
>             prefWidth -= getSpacing();
>         } else {
> 
> 
> the general issue, in my opinion, is that doing `prefWidth += snapSizeX(node.prefWidth(-1)) + getSpacing();` results in the `prefWidth` value differ from its snapped value.  In other words, whenever computation involves snapped values, the result must be snapped as well - and that includes the case when all the parts of the computation are snapped.
> 
> Another, related, topic is how to properly snap the values in the computation.  I would say ideally it should be done like this:
> 
> 
> snappedResult = snap(snap(value1) .OP. snap(value2) .OP. ... snap (valueN))
> 
> 
> It might be possible to skip the snapping of intermediary values, and only snap the result, but one must be careful not to accumulate errors.
> 
> Getting back to the ToolBarSkin, one can see the issue on LL392, 399, 411, 417, 425, 436, 530, and so on.
> 
> I decided not to fix the snapping for the purpose of making this PR narrow in scope with the goal to backport it to jfx25, but I did want to describe the issue.

@arapte Can you review this?

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PR Comment: https://git.openjdk.org/jfx/pull/1856#issuecomment-3127180350