8178297: TableView scrolls slightly when adding new elements

[jperedadnr]

This PR fixes an issue that happens when adding new items to a TableView or any other control that uses VirtualFlow, if the scroll position is not 0: the virtual flow is slightly shifted down.

For instance, let's say that a cell has a layoutY of -10.0. After adding a new item to the table, during the layout pass the new value is initially modified to -9.999999999999996 (VirtualFlow::adjustByPixelAmount) , and then, after calling VirtualFlow::positionCell (that uses snapSizeY(position)) the layoutY is modified to -9.5, causing an undesired positive shift of 0.5 pixels.

Region has different snap methods: snapSizeX/Y are used to snap node dimension values, like width or height, by ceiling to the nearest pixel (which explains the -9.5 value), while snapSpaceX/Y are used to snap position values like insets, by rounding to the nearest pixel (this will give the expected -10.0).

Therefore, this PR modifies VirtualFlow::positionCell to use the snapSpaceX/Y methods, since these are being used to set the layout of the cell and not its size.

Test: A unity test has been included. It simulates the case of adding new items to the virtual flow after an initial scroll.
It currently fails after adding a few items, and it passes with the changes of this PR.

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change must be properly reviewed

Issue

• JDK-8178297: TableView scrolls slightly when adding new elements

Reviewers

• Kevin Rushforth (@kevinrushforth - Reviewer)
• Ajit Ghaisas (@aghaisas - Reviewer)

Download

$ git fetch https://git.openjdk.java.net/jfx pull/297/head:pull/297
$ git checkout pull/297

[bridgekeeper]

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[mlbridge]

Webrevs

• 01: Full (72e2849)
• 00: Full (cdde496)

[kevinrushforth]

/reviewers 2

[openjdk]

@kevinrushforth
The number of required reviews for this PR is now set to 2 (with at least 1 of role reviewers).

[openjdk]

@jperedadnr this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout 8178297-virtualflow
git fetch https://git.openjdk.java.net/jfx master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

[kevinrushforth]

Looks good.

[openjdk]

@jperedadnr This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8178297: TableView scrolls slightly when adding new elements

Reviewed-by: kcr, aghaisas

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 7 new commits pushed to the master branch:

• a56ba63: 8254255: Remove obsolete .hgignore file
• 184f12c: 8252192: Update to Visual Studio 2019 version 16.7.2
• 7857022: 8251946: ObservableList.setAll does not conform to specification
• 1c485a3: 8252191: Update to gcc 10.2 on Linux
• 15e52d8: 8253696: WebEngine refuses to load local "file:///" CSS stylesheets when using JDK 15
• 5b42b64: 8252236: TabPane: must keep header of selected tab visible
• 77a183e: 8209788: Left/Right/Ctrl+A keys not working in editor of ComboBox if popup showing

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch.
As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[jperedadnr]

/integrate

[openjdk]

@jperedadnr Since your change was applied there have been 7 commits pushed to the master branch:

• a56ba63: 8254255: Remove obsolete .hgignore file
• 184f12c: 8252192: Update to Visual Studio 2019 version 16.7.2
• 7857022: 8251946: ObservableList.setAll does not conform to specification
• 1c485a3: 8252191: Update to gcc 10.2 on Linux
• 15e52d8: 8253696: WebEngine refuses to load local "file:///" CSS stylesheets when using JDK 15
• 5b42b64: 8252236: TabPane: must keep header of selected tab visible
• 77a183e: 8209788: Left/Right/Ctrl+A keys not working in editor of ComboBox if popup showing

Your commit was automatically rebased without conflicts.

Pushed as commit 205e4b9.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.