RFR: 8366739: ToolBar: overflow menu with fractional scale (2)

[John Hendrikx]

On Sun, 21 Dec 2025 02:42:12 GMT, Cormac Redmond <duke at openjdk.org> wrote:

> Fix overflow menu triggering due to floating-point precision error.
> 
> At 1.25 display scaling on Windows, floating-point comparison errors (e.g. 109.60000000000001 > 109.6) cause the overflow menu to appear when the lefthand value is regarded as larger than the righthand value.
> 
> These should be treated as equal (and therefore not display the overflow menu).
> 
> This bug can happen in both horizontal and vertical toolbar orientation.
> 
> The new tests added fail without this fix, and pass with it. An existing test has been re-factored slightly to allow re-use and more flexibility in specifying the scene's root node.

LGTM, thanks for the fix!

modules/javafx.controls/src/main/java/javafx/scene/control/skin/ToolBarSkin.java line 706:

> 704:             // Use a small epsilon (1e-9 / 0.000000001) to tolerate floating-point rounding error when comparing
> 705:             // doubles. E.g. 117.60000000000001 should be regarded as equal to 117.6.
> 706:             if (x - length > 1e-9) {

We don't really use tolerances like this in the UI code; instead the problem is almost always because some floating point operations were done, but the result wasn't (re)snapped.

In the code above I see that `x` is modified without re-snapping.  I think a `snapPositionX/Y` should be applied on `x`, something like this:

            if (node.isManaged()) {
                if (getSkinnable().getOrientation() == Orientation.VERTICAL) {
                    x += snapPositionY(snapSizeY(node.prefHeight(-1)) + getSpacing());
                } else {
                    x += snapPositionX(snapSizeX(node.prefWidth(-1)) + getSpacing());
                }
            }

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Marked as reviewed by jhendrikx (Reviewer).

PR Review: https://git.openjdk.org/jfx/pull/2016#pullrequestreview-3601701580
PR Review Comment: https://git.openjdk.org/jfx/pull/2016#discussion_r2637521921