Improve `TextPainter.layout` caching #118128

LongCatIsLooong · 2023-01-07T00:53:56Z

Improves TextPainter.layout caching when only the input constraints change:

removes the double layout calls in TextPainter._layoutParagraph: now double layout is only needed when TextAlign is not left, and the input maxWidth == double.infinity.
skip calls to ui.Paragraph.layout when it's guaranteed that there's no soft line breaks before/after the layout call.

This doesn't introduce new APIs but may slightly shift text rendered on screen.
This reduces the number of layout calls but since shaping results are already cached so it only skips the relatively cheap line-breaking process when possible.

528 scuba failures but all of them seem reasonable.

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I read the Contributor Guide and followed the process outlined there for submitting PRs.
I read the Tree Hygiene wiki page, which explains my responsibilities.
I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
I signed the CLA.
I listed at least one issue that this PR fixes in the description above.
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…ature

Hixie · 2023-01-10T00:02:57Z

packages/flutter/lib/src/painting/text_painter.dart

we really should stop doing this

also the comment is just wrong (it's been wrong for a long time). we looked at doing what it says, but we decided not to, many years ago. if we're going to make a breaking change anyway, we might as well remove this at the same time...

based on the conversation in #31707, it doesn't seem to be safe to remove this hack yet, since widths/maxIntrinsicWidths are reported in floats and the input widths are doubles

After removing the rounding in the framework and skparagraph, and tuning down the harfbuzz scale from 1^16 to 1^10, with this change there are only 50 framework failures and nothing seems to be overflowing. So I guess that's doable but I'd like to try to do that in a separate PR.

@Hixie still this breaks 500+ scuba tests. But I'm not sure how I can write a migration guide for this one.

Hixie · 2023-01-10T00:05:08Z

packages/flutter/lib/src/painting/text_painter.dart

(nit: extraneous spaces after //)

Hixie · 2023-01-10T00:05:53Z

packages/flutter/lib/src/painting/text_painter.dart

not sure what this comment means

removed. I thought if the text doesn't contain hard breaks the extra width will be distributed among the whitespaces in that line, but turns out the end of line is counted as a hard break so when maxWidth > maxIntrinsicWidth it's the same as TextAlign.start.

Hixie · 2023-01-10T00:06:14Z

packages/flutter/lib/src/painting/text_painter.dart

for clarity it might be good to say 0.0 and 1.0 instead of 0 and 1 when they're doubles

Hixie · 2023-01-10T00:07:03Z

packages/flutter/lib/src/painting/text_painter.dart

this might be clearer?

Suggested change

final List<TextBox> rawBoxes = layout._inlinePlaceholderBoxes

??= layout.paragraph.getBoxesForPlaceholders();

layout._inlinePlaceholderBoxes ??= layout.paragraph.getBoxesForPlaceholders();

final List<TextBox> rawBoxes = layout._inlinePlaceholderBoxes;

_inlinePlaceholderBoxes's type is List<TextBox>? so I would have to use !.

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LongCatIsLooong added 14 commits December 21, 2022 00:39

Avoid affinity like the plague

c90738c

ignore lint

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clean up

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fix test

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review

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Merge remote-tracking branch 'upstream/master' into TextBoundary-sign…

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…ature

Move wordboundary to text painter

1ada762

docs

978e4d3

fix tests

c8d733b

wip

d344b2a

Merge remote-tracking branch 'upstream/master' into text-layout

c452e0f

fix tests

6d0cee7

test

f6cb305

remove stuff

8531a11

flutter-dashboard bot added a: text input Entering text in a text field or keyboard related problems f: material design flutter/packages/flutter/material repository. framework flutter/packages/flutter repository. See also f: labels. labels Jan 7, 2023

LongCatIsLooong closed this Jan 7, 2023

LongCatIsLooong added 2 commits January 9, 2023 13:42

fix tests

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add tests

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LongCatIsLooong changed the title ~~Less ui.Paragraph.layout calls.~~ Reduce ui.Paragraph.layout calls, make it less destructive Jan 9, 2023

LongCatIsLooong reopened this Jan 9, 2023

LongCatIsLooong changed the title ~~Reduce ui.Paragraph.layout calls, make it less destructive~~ Improve ui.Paragraph.layout caching Jan 9, 2023

LongCatIsLooong changed the title ~~Improve ui.Paragraph.layout caching~~ Improve TextPainter.layout caching Jan 9, 2023

docs

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Hixie reviewed Jan 10, 2023

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-    final List<TextBox> rawBoxes = layout._inlinePlaceholderBoxes
-                               ??= layout.paragraph.getBoxesForPlaceholders();
+    layout._inlinePlaceholderBoxes ??= layout.paragraph.getBoxesForPlaceholders();
+    final List<TextBox> rawBoxes = layout._inlinePlaceholderBoxes;

Improve TextPainter.layout caching #118128

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Improve `TextPainter.layout` caching #118128

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