8349188: LineBorder does not scale correctly #26025

rajamah · 2025-06-27T18:11:46Z

Modified the code to account for border thickness correctly and updated the related tests to make sure we are testing the new change.

Testing done.

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Issue

JDK-8349188: LineBorder does not scale correctly (Bug - P3)

Reviewers

Alexey Ivanov (@aivanov-jdk - Reviewer)
Sergey Bylokhov (@mrserb - Reviewer)

Contributors

Alexey Ivanov <[email protected]>

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bridgekeeper · 2025-06-27T18:12:22Z

👋 Welcome back rmahajan! 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.

openjdk · 2025-06-27T18:12:54Z

@rajamah 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:

8349188: LineBorder does not scale correctly

Co-authored-by: Alexey Ivanov <[email protected]>
Reviewed-by: aivanov, serb

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 207 new commits pushed to the master branch:

5e40fb6: 8277394: Remove the use of safepoint_workers in reference processor
2528c62: 8361198: [AIX] fix misleading error output in thread_cpu_time_unchecked
1be29bd: 8361060: Keep track of the origin server against which a jdk.internal.net.http.HttpConnection was constructed
... and 204 more: https://git.openjdk.org/jdk/compare/26848a7d6ce4c573b679a690fd36e6d7082243f6...master

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openjdk · 2025-06-27T18:13:27Z

@rajamah The following label will be automatically applied to this pull request:

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rajamah · 2025-06-27T18:18:57Z

/contributor add @aivanov-jdk

openjdk · 2025-06-27T18:19:25Z

@rajamah
Contributor Alexey Ivanov <[email protected]> successfully added.

mlbridge · 2025-06-27T18:30:35Z

Webrevs

aivanov-jdk

Looks good except for a few nits.

src/java.desktop/share/classes/javax/swing/border/LineBorder.java

test/jdk/javax/swing/border/LineBorder/ScaledLineBorderTest.java

src/java.desktop/share/classes/javax/swing/border/LineBorder.java

Co-authored-by: Alexey Ivanov <[email protected]>

mrserb · 2025-06-28T04:26:31Z

src/java.desktop/share/classes/javax/swing/border/LineBorder.java

            Shape inner;

-            int offs = this.thickness * (int) scaleFactor;
+            int offs = clipRound(this.thickness * scaleFactor);


Please double-check whether you need to use Region.clipScale() instead.

I actually do not remember when to use one over the other. Maybe if you find a review request for the patch where these methods were added, you can confirm which one should be used. I checked the current source, and it seems that we randomly use one or the other, which seems incorrect.

it might be possible we should use one for the left/top part and another for the right/bottom so we will not create a gaps.

Please double-check whether you need to use Region.clipScale() instead.

@mrserb We use Region.clipRound for converting coordinates in SwingUtilities3.paintBorder:

jdk/src/java.desktop/share/classes/com/sun/java/swing/SwingUtilities3.java

Lines 231 to 236 in a23de2e

double xx = at.getScaleX() * x + at.getTranslateX();

double yy = at.getScaleY() * y + at.getTranslateY();

xtranslation = clipRound(xx);

ytranslation = clipRound(yy);

width = clipRound(at.getScaleX() * w + xx) - xtranslation;

height = clipRound(at.getScaleY() * h + yy) - ytranslation;

These formulas were introduced in #10681 (JDK-8282958); and after refactoring #11571 (JDK-8294680), the new formulas resolved JDK-8294921 after #7449 (JDK-8279614) where there was a gap between the component edge and its border. These formulas specifically addressed the situation with gaps and were developed while we worked on making LineBorder and EtchedBorder render better at fractional scales.

So, using clipRound seems good enough. Initially, I suggested using (int) (this.thickness * scaleFactor), but clipRound gives better results.

I actually do not remember when to use one over the other. Maybe if you find a review request for the patch where these methods were added, you can confirm which one should be used.

I couldn't find anything explaining where clipScale is better than clipRound. The discussion for JDK-8000629 started in March 2013 and continued in April 2013.

I checked the current source, and it seems that we randomly use one or the other, which seems incorrect.

The javadoc for neither clipScale nor clipRound provides an example where each method is best suitable. So, it's not that surprising either is used randomly…

It seems to me, that both clipScale and clipRound yield the same result. The former uses Math.round, whereas the latter uses Math.ceil after subtracting 0.5.

it might be possible we should use one for the left/top part and another for the right/bottom so we will not create a gaps.

Perhaps… However, I'm pretty sure gaps are still possible whatever method we choose because fractional pixels don't fit nicely into the pixel grid.

I am pretty sure these methods produce different results for negative coordinates.

probably these discussions may help
https://mail.openjdk.org/pipermail/2d-dev/2016-July/007152.html
https://mail.openjdk.org/pipermail/2d-dev/2016-October/007764.html

@mrserb Putting the discussions aside, does the suggested fix look good to you?

As I said, border painting uses clipRound consistently: both in coordinate calculation and in thickness calculation. This approach resolves the problem reported.

Looking at descriptions of clipScale and clipRound, it seems the former suits better… Yet it makes the rendering less consistent with other borders: using clipScale switches to 2-pixel and 3-pixel border at 1.50 and 2.50 correspondingly (from 1 and 2 with clipRound). In other cases, the border thickness also increases, which may be undesirable.

Overall, there are 6 failures of the ScaledLineBorderTest.java test when the code in JDK uses clipScale instead of clipRound.

I looked at another test case Rajat and I discussed, and using clipScale doesn't help there either. I prefer rendering with clipRound.

My point is to investigate the difference between clipScale and clipRound to ensure the correct one is used. There was a complex discussion before about similar issue, which is why we currently have two separate versions of this rounding logic. Simply replacing one with the other might not work and some other tweaks should be done.

My point is clipRound works good in this use case, it resolves the problem, I see no reason not to accept the fix.

I agree with your general concern that we should understand better the purpose of each method. Yet no one seems to remember the outcome of that complex discussion, therefore switching to clipScale could be postponed; if it's deemed necessary, we can easily change the method, both in the implementation and in the test.

I submitted JDK-8361095 to ensure this current discussion isn't forgotten and we figure out the purpose and guidelines for clipScale and clipRound.

Ok sounds good.

rajamah · 2025-07-02T19:20:23Z

/integrate

aivanov-jdk · 2025-07-03T14:22:56Z

Nudge the Skara bots with a comment…

openjdk · 2025-07-03T14:23:59Z

@rajamah
Your change (at version f6af4cb) is now ready to be sponsored by a Committer.

aivanov-jdk · 2025-07-03T14:24:18Z

/sponsor

openjdk · 2025-07-03T14:24:54Z

Going to push as commit 24117c6.
Since your change was applied there have been 207 commits pushed to the master branch:

5e40fb6: 8277394: Remove the use of safepoint_workers in reference processor
2528c62: 8361198: [AIX] fix misleading error output in thread_cpu_time_unchecked
1be29bd: 8361060: Keep track of the origin server against which a jdk.internal.net.http.HttpConnection was constructed
... and 204 more: https://git.openjdk.org/jdk/compare/26848a7d6ce4c573b679a690fd36e6d7082243f6...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-07-03T14:25:02Z

@aivanov-jdk @rajamah Pushed as commit 24117c6.

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

8349188: Expand bug8033699.java to iterate over all LaFs

c81deaa

openjdk bot added the rfr Pull request is ready for review label Jun 27, 2025

openjdk bot added the client [email protected] label Jun 27, 2025

rajamah changed the title ~~8349188: Expand bug8033699.java to iterate over all LaFs~~ 8349188: LineBorder does not scale correctly Jun 27, 2025

Update ScaledTextFieldBorderTest.java

0123071

aivanov-jdk suggested changes Jun 27, 2025

View reviewed changes

rajamah and others added 4 commits June 27, 2025 12:38

Update src/java.desktop/share/classes/javax/swing/border/LineBorder.java

8ce609e

Co-authored-by: Alexey Ivanov <[email protected]>

Update test/jdk/javax/swing/border/LineBorder/ScaledLineBorderTest.java

ce44503

Co-authored-by: Alexey Ivanov <[email protected]>

Update test/jdk/javax/swing/border/LineBorder/ScaledLineBorderTest.java

4dd9a0f

Co-authored-by: Alexey Ivanov <[email protected]>

fix blank line

f6af4cb

mrserb reviewed Jun 28, 2025

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aivanov-jdk approved these changes Jun 28, 2025

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mrserb approved these changes Jul 2, 2025

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	double xx = at.getScaleX() * x + at.getTranslateX();
	double yy = at.getScaleY() * y + at.getTranslateY();
	xtranslation = clipRound(xx);
	ytranslation = clipRound(yy);
	width = clipRound(at.getScaleX() * w + xx) - xtranslation;
	height = clipRound(at.getScaleY() * h + yy) - ytranslation;

8349188: LineBorder does not scale correctly #26025

8349188: LineBorder does not scale correctly #26025

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