RFR: 8199592: Control labels truncated at certain DPI scaling levels

[Jose Pereda]

On Sun, 25 Oct 2020 11:14:43 GMT, Jeanette Winzenburg <fastegal at openjdk.org> wrote:

>> The approach looks good. I'll review it early next week, and also ask @arapte to review.
>
> curious: it this expected to fix the ellipsed checkBox texts? Can verify that the test fails/passes before/after the fix, but the example in the report looks still is eclipsed: same for 1.5, slightly better (in that only the first text is eclipsed compared to the first 3 without) for 1.75 scaling. What am I missing?

@kleopatra Thanks for checking. 

As discussed in the JBS issue, there is a call in `CheckBoxSkin::layoutChildren` that, probably by mistake, calls `snapSizeX` twice, and that gives different results when a different UI scale is used.

This PR applies to the snapSizeXX methods, so it is guaranteed that `snapSizeXX(snapSizeXX(a)) == snapSizeXX(a)`. With the included test, _this_ issue should now be fixed.

However, you are totally right, the CheckBox test from the JBS issue only works fine with this PR either if `Stage::sizeToScene` is called or if the Scene is created with a defined width, so we still have another issue laying around.

Running the CheckBox test on Windows with 1.75% UI scale and without calling `sizeToScene`, produces this log of width and height values: 

Scene::resizeRootOnSceneSizeChange 256.0, 33.0
...
Scene::resizeRootOnSceneSizeChange 256.0, 33.0
...
// WindowEvent.RESIZE event UI scale 1.75
...
Scene::resizeRootOnSceneSizeChange 256.0, 33.14285659790039

Both values should be snapped, as these are generated with snap methods in HBox. However, this is not the case for height, as there are some conversions in between:  This 33.14285659790039 value comes from an int (`View`: height = (int) (33.0 x 1.75) = 58) to float (`TKSceneListener`: h = 33.142857) to double (`Scene` width = 33.14285659790039). However, the proper snapped value should be 33.14285714285714.

However, if we add a call to  `stage.sizeToScene()`, then the log is:

Scene::resizeRootOnSceneSizeChange 256.0, 33.0
...
Scene::resizeRootOnSceneSizeChange 256.0, 33.0
...
Scene::resizeRootOnSceneSizeChange 256.0, 33.14285659790039
...
Scene::resizeRootOnSceneSizeChange 257.1428571428571, 33.14285714285714
...
Scene::resizeRootOnSceneSizeChange 257.1428571428571, 33.14285714285714
...
both width and height have stable snapped values, and the checkbox layout is correct.

Back to the 256.0 value of width, this value comes from margin (8.0 * 2) + controls width(54.0 * 4)  + spacing (8.0 * 3), but the value 54.0 is not properly computed, as at this point the UI scale is still 1.0. 
Once the UI scale is set to 1.75 the checkBox width is 54.285714285714285, and the scene's width is 257.14285714285714.

So the issue can be related to the UI scale value taken into account too late, and how this change doesn't trigger an update of the scene. 

Does it make sense to address this issue with the current PR?

-------------

PR: https://git.openjdk.java.net/jfx/pull/336