RichTextArea: How to return existing paragraphs from SyntaxDecorator?
Andy Goryachev
andy.goryachev at oracle.com
Tue Apr 29 18:04:15 UTC 2025
You *do not* want to update javaFX in a background thread.
The idea is to compute the syntax in a background thread (provided the underlying model is properly synchronized and can serve the plain text paragraphs to multiple threads), but the actual change must take effect in the FX application thread.
-andy
From: openjfx-dev <openjfx-dev-retn at openjdk.org> on behalf of PavelTurk <pavelturk2000 at gmail.com>
Date: Tuesday, April 29, 2025 at 10:54
To: openjfx-dev at openjdk.org <openjfx-dev at openjdk.org>
Subject: Re: RichTextArea: How to return existing paragraphs from SyntaxDecorator?
Thank you very much for such detailed answer!
On 4/29/25 20:15, Andy Goryachev wrote:
If you can guarantee that nothing in the paragraph has changed, the model can return a cached paragraph.
The problem is it doesn't return. As I've said earlier the problem is in this line - However, it didn't work because of this line - https://github.com/openjdk/jfx/blob/3fdd21386d6db96294fcecd80afc25d09732c067/modules/jfx.incubator.richtext/src/main/java/jfx/incubator/scene/control/richtext/model/CodeTextModel.java#L83 and as a result -> StackOverflow.
But if the particular paragraph has changed in any way, it might impact other things like the scrollbars.
I suppose it is possible to implement certain optimizations if, for example, the overall dimensions do not change - like, for example, if the style changes only affect the text colors and nothing else.
One can also try to query the view for which paragraphs are visible and which are not, but keep in mind that the same model can be visualized by different views - you should be fine as long as your application can guarantee that there is only one view.
Getting back to syntax highlighting of large models, I envisioned that the background thread that computes the highlighting updates the model periodically and in (large) blocks, to minimize the load, and to strike the balance between quality and performance. Also, when dealing with large text that might contain comments, the syntax highlighter may want to keep track of the nexus points from which the syntax computation can be re-started instead of re-scanning the file from the beginning. All this might get complicated rather quickly though.
Yes, I am working on highlighting now and I add highlighting in SyntaxDecorator on JavaFX thread:
@Override
public RichParagraph createRichParagraph(CodeTextModel model, int index) {
RichParagraph.Builder b = RichParagraph.builder();
for (segment: segments) {
b.addWithStyleNames(segment.getText(), segment.getStyles().toArray(String[]::new));
}
return b.build();
}
}
Important! I use only style classes (no java, no inline style).
Segments - already ready model. Can such code create performance problems, including scrolling? I mean, that as I understand there are TWO ways to add styles:
1) on JavaFX thread 2) on background thread. I optimized my code model (providing ready segments) to the maximum, and I think the code must work well on JavaFX thread.
But it doesn't - I tested code with about 6 000 paragraphs. At the same time the same approach works without performance problems in RTFX.
Best regards, Pavel
-andy
From: openjfx-dev <openjfx-dev-retn at openjdk.org><mailto:openjfx-dev-retn at openjdk.org> on behalf of PavelTurk <pavelturk2000 at gmail.com><mailto:pavelturk2000 at gmail.com>
Date: Tuesday, April 29, 2025 at 08:39
To: openjfx-dev at openjdk.org<mailto:openjfx-dev at openjdk.org> <openjfx-dev at openjdk.org><mailto:openjfx-dev at openjdk.org>
Subject: Re: RichTextArea: How to return existing paragraphs from SyntaxDecorator?
Andy, thank you for your reply
On 4/29/25 18:02, Andy Goryachev wrote:
Multiple topics here.
1. The view does size 100 paragraphs (Params.SLIDING_WINDOW_EXTENT) to ensure smooth scrolling when text wrap is on. Initially I thought we could allow the application to control this parameter, but we decided against it, as it exposes internal aspect of the implementation.
2. You probably should not cache the paragraphs in the model, or try to optimize the styling in the way I understood you did. When the view asks for the paragraph, the model needs to render it in all its glory, or things would break.
It looks you are trying to implement the syntax highlighting, right? The first question you might want to ask is determine whether the styles are known at the time when the paragraph gets requested. If not - you probably want to return a plain text paragraph, that is with no styling, and once the styling is known, fire the model's style change event, which will cause the view to request the (newly updated) paragraphs it needs. In other words, the code you supplied won't work - the model should always build a new paragraph (or supply a cached one only if you can guarantee that nothing in it changed, not event line index).
Hm. I've read this line - https://github.com/openjdk/jfx/blob/3fdd21386d6db96294fcecd80afc25d09732c067/modules/jfx.incubator.richtext/src/main/java/jfx/incubator/scene/control/richtext/model/RichParagraph.java#L42 saying that paragraph is IMMUTABLE and decided - why should I recreate it if it hasn't changed. It seems that I was wrong. At the same time in RTFX you can control what to update
and what not. I mean:
public class ParagraphStyler implements Consumer<ListModification<? extends Paragraph<Collection<String>, String, Collection<String>>>> {
@Override
public void accept(ListModification<? extends Paragraph<Collection<String>, String, Collection<String>>> lm) {
//here it is possible to update styles only for paragraphs which styles should be updated
}
}
codeArea.getVisibleParagraphs().addModificationObserver(new ParagraphStyler()); //only for visible paragraphs!
In other words, JFX CodeArea forces paragraph styles to update whether it’s necessary or not, whereas in RTFX we can optimize this process—at least, that’s how I understand it.
3. Not sure about the scrolling, it seems to work on macOS as expected. Does it work with a stock model that has none of the "optimizations"?
-andy
Best regards, Pavel
From: openjfx-dev <openjfx-dev-retn at openjdk.org><mailto:openjfx-dev-retn at openjdk.org> on behalf of PavelTurk <pavelturk2000 at gmail.com><mailto:pavelturk2000 at gmail.com>
Date: Monday, April 28, 2025 at 16:54
To: openjfx-dev at openjdk.org<mailto:openjfx-dev at openjdk.org> <openjfx-dev at openjdk.org><mailto:openjfx-dev at openjdk.org>
Subject: RichTextArea: How to return existing paragraphs from SyntaxDecorator?
I noticed that paragraphs in CodeArea are updated too aggressively. For example, when I press a single key like '1', about 100 paragraphs get refreshed.
To improve performance, I decided to implement it this way: I store information for each paragraph indicating whether its styles are up-to-date or not.
From SyntaxDecorator, I return the existing paragraph from the model if the styles are valid. If the styles are outdated, I build a new paragraph.
Something like this:
codeArea.setSyntaxDecorator(new SyntaxDecorator() {
@Override
public RichParagraph createRichParagraph(CodeTextModel model, int index) {
if (paragraphStylesAreValid) {
return codeArea.getModel().getParagraph(index);
} else {
RichParagraph.Builder b = RichParagraph.builder();
...
return b.build();
}
}
@Override
public void handleChange(CodeTextModel m, TextPos start, TextPos end, int charsTop,
int linesAdded, int charsBottom) {
}
});
However, it didn't work because of this line - https://github.com/openjdk/jfx/blob/3fdd21386d6db96294fcecd80afc25d09732c067/modules/jfx.incubator.richtext/src/main/java/jfx/incubator/scene/control/richtext/model/CodeTextModel.java#L83
As I result I get StackOverflowError. Could anyone say how to do it?
Best regards, Pavel
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