8089589: [ListView] ScrollBar content moves toward-backward during scrolling. #398

johanvos · 2021-02-09T12:21:28Z

This PR introduces a refactory for VirtualFlow, fixing a number of issues reported about inconsistent scrolling speed (see https://bugs.openjdk.java.net/browse/JDK-8089589)
The problem mentioned in the JBS issue (and in related issues) is that the VirtualFlow implementation depends on cell index and cell count, instead of on pixel count. The latter is unknown when the VirtualFlow is created, and pre-calculating the size of a large set of items would be very expensive.
Therefore, this PR uses a combination of a gradual calculation of the total size in pixels (estimatedSize) and a smoothing part that prevents the scrollback to scroll in the reverse direction as the requested change.
This PR currently breaks a number of tests that hard-coded depend on a number of evaluations. This is inherit to the approach of this PR: if we want to estimate the total size, we need to do some additional calculations. In this PR, I try to balance between consistent behavior and performance.

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Issue

JDK-8089589: [ListView] ScrollBar content moves toward-backward during scrolling.

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

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bridgekeeper · 2021-02-09T12:21:41Z

👋 Welcome back jvos! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

* release accumCell and empty parent when invalidating CellFactory

mlbridge · 2021-02-15T21:16:54Z

Webrevs

kevinrushforth · 2021-02-16T12:31:33Z

/reviewers 2

openjdk · 2021-02-16T12:31:53Z

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

kevinrushforth

I reviewed the code, and tested this, both using automated tests and various manual tests, and it looks good to me. In addition to the simple test attached to the bug report, I can reproduce the bug with HelloTableView and the HorizontalListView sample of Ensemble8.

HelloTableView

Run HelloTableview program
Sort by first name
Slowly scroll down by dragging the thumb
BUG: the scrolling jitters slightly when you reach the taller row (Jacob Smith Smith Smith)

Ensemble8

Run Ensemble8 and select HorizontalListView sample
Scroll all the way to the right
Slowly scroll to the left by dragging the thumb
BUG: the scrolling jitters slightly when you reach the wider row (Long Row 3)

All three test cases run fine with the fix.

I left a few inline questions and comments (mostly about code style w.r.t., inline whitespace, and a couple typos).

modules/javafx.controls/src/test/java/test/javafx/scene/control/skin/VirtualFlowTest.java

modules/javafx.controls/src/main/java/javafx/scene/control/skin/VirtualFlow.java

kevinrushforth · 2021-04-09T22:33:29Z

modules/javafx.controls/src/main/java/javafx/scene/control/skin/VirtualFlow.java

-        return (int) (getPosition() * getCellCount());
+        double total = 0;
+        int currentCellCount = getCellCount();
+        double estSize = estimatedSize/currentCellCount;


MInor: missing spaces before and after /

kevinrushforth · 2021-04-09T22:42:11Z

modules/javafx.controls/src/main/java/javafx/scene/control/skin/VirtualFlow.java

+        }
+        // Make sure we have enough space in the cache to store this index
+        while (idx >= itemSizeCache.size()) {
+            itemSizeCache.add(itemSizeCache.size(), null);


Can this be simplified to itemSizeCache.add(null);?

That won't add enough elements. For example, in case idx = 10, and the itemSizeCache has 5 elements, we need to add 5 empty elements to the cache, as they might get queried/pushed, e.g. we might do
itemSizeCache.set(7, 123.45);

Sure, that's why you need the while loop. What I meant is that the following two calls are equivalent for any list:

list.add(list.size(), null);

and

list.add(null);

johanvos · 2021-04-12T09:37:54Z

Thanks for the review. I answered the questions, and corrected the styling errors.

kevinrushforth

Thanks for the explanations about the algorithm. I have no more questions on the logic.

I think Ajit will review this later this week.

Btw, I did another pass over the code and noted a few more formatting inconsistencies (missing spaces).

modules/javafx.controls/src/main/java/javafx/scene/control/skin/VirtualFlow.java

kevinrushforth · 2021-04-12T13:15:26Z

modules/javafx.controls/src/main/java/javafx/scene/control/skin/VirtualFlow.java

+        if (viewportLength >= estimatedSize) {
+            setPosition(0.);
+        } else {
+            setPosition(absoluteOffset/(estimatedSize - viewportLength));


Minor: spacing

modules/javafx.controls/src/main/java/javafx/scene/control/skin/VirtualFlow.java

aghaisas

Code changes are OK. I have noted a few minor comments.

modules/javafx.controls/src/test/java/test/javafx/scene/control/skin/VirtualFlowTest.java

modules/javafx.controls/src/main/java/javafx/scene/control/skin/VirtualFlow.java

modules/javafx.controls/src/test/java/test/javafx/scene/control/skin/VirtualFlowTest.java

openjdk · 2021-04-16T12:37:40Z

@johanvos 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:

8089589: [ListView] ScrollBar content moves toward-backward during scrolling.

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 44 new commits pushed to the master branch:

05ab799: 8208088: Memory Leak in ControlAcceleratorSupport
e8689fe: 8265031: Change default macOS min version for x86_64 to 10.12 and aarch64 to 11.0
c8384a1: 8264928: Update to Xcode 12.4
808b107: 8260245: Update ICU4C to version 68.2
d808dd1: 8258663: Fixed size TableCells are not removed from sene graph when column is removed
28475cb: 8263807: Button types of a DialogPane are set twice, returns a wrong button
cc94e96: 8217955: Problems with touch input and JavaFX 11
9796a83: 8263322: Calling Application.launch on FX thread should throw IllegalStateException, but causes deadlock
5898858: 8263169: [macos] JavaFX windows open as tabs when system preference for documents is set
e63931e: 8262366: Update glib to version 2.66.7
... and 34 more: https://git.openjdk.java.net/jfx/compare/d4058a181a16615d604582f95d4fc2be6bda98ab...master

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.

johanvos · 2021-04-16T13:38:34Z

/integrate

openjdk · 2021-04-16T13:39:20Z

@johanvos Since your change was applied there have been 44 commits pushed to the master branch:

05ab799: 8208088: Memory Leak in ControlAcceleratorSupport
e8689fe: 8265031: Change default macOS min version for x86_64 to 10.12 and aarch64 to 11.0
c8384a1: 8264928: Update to Xcode 12.4
808b107: 8260245: Update ICU4C to version 68.2
d808dd1: 8258663: Fixed size TableCells are not removed from sene graph when column is removed
28475cb: 8263807: Button types of a DialogPane are set twice, returns a wrong button
cc94e96: 8217955: Problems with touch input and JavaFX 11
9796a83: 8263322: Calling Application.launch on FX thread should throw IllegalStateException, but causes deadlock
5898858: 8263169: [macos] JavaFX windows open as tabs when system preference for documents is set
e63931e: 8262366: Update glib to version 2.66.7
... and 34 more: https://git.openjdk.java.net/jfx/compare/d4058a181a16615d604582f95d4fc2be6bda98ab...master

Your commit was automatically rebased without conflicts.

Pushed as commit 8e54757.

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

mstr2 · 2021-11-03T19:17:07Z

modules/javafx.controls/src/main/java/javafx/scene/control/skin/VirtualFlow.java

+        // When the position is changed explicitly, we need to make sure
+        // the absolute offset is changed accordingly.
+        adjustAbsoluteOffset();
+    }


This seems to violate the invariant setPosition(...) ≙ positionProperty().set(...).

Your comment indicates that this is by design, but how do you prevent people from invoking positionProperty().set(...) and getting a different behavior?

VirtualFlow refactory to pixel-based calculations

419c845

johanvos added 4 commits February 12, 2021 22:10

fix a few more tests.

13c9fda

Fix whitespace issues

dfe04e6

* fix failing tests by hard-coding new count values.

8bfd8b9

* release accumCell and empty parent when invalidating CellFactory

fix whitespace issues

248d0f0

johanvos changed the title ~~[WIP] 8089589: [ListView] ScrollBar content moves toward-backward during scrolling.~~ 8089589: [ListView] ScrollBar content moves toward-backward during scrolling. Feb 15, 2021

openjdk bot added the rfr Ready for review label Feb 15, 2021

kevinrushforth requested review from kevinrushforth and aghaisas February 16, 2021 12:32

kevinrushforth reviewed Apr 9, 2021

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modules/javafx.controls/src/test/java/test/javafx/scene/control/skin/VirtualFlowTest.java Outdated Show resolved Hide resolved

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aghaisas approved these changes Apr 16, 2021

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openjdk bot closed this Apr 16, 2021

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8089589: [ListView] ScrollBar content moves toward-backward during scrolling. #398

8089589: [ListView] ScrollBar content moves toward-backward during scrolling. #398

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mstr2 Nov 3, 2021

8089589: [ListView] ScrollBar content moves toward-backward during scrolling. #398

8089589: [ListView] ScrollBar content moves toward-backward during scrolling. #398

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