On Mon, 19 May 2025 12:26:54 GMT, Daniel Gredler <dgred...@openjdk.org> wrote:
>> `LineBreakMeasurer.nextLayout()` calls `nextOffset()` internally to
>> calculate the layout limit. When this happens, a `GlyphVector` is created
>> and the layout engine is invoked to shape the text. The `GlyphVector` is
>> cached in the relevant `ExtendedTextSourceLabel` component.
>>
>> `LineBreakMeasurer.nextLayout()` then calls `TextMeasurer.getLayout()` which
>> eventually asks that same `ExtendedTextSourceLabel` component for a subset
>> component. This triggers the creation of a fresh `ExtendedTextSourceLabel`
>> without the cached `GlyphVector`.
>>
>> However, this fresh `ExtendedTextSourceLabel` is not necessary if the subset
>> requested perfectly matches the already-existing `ExtendedTextSourceLabel`
>> component. This happens when the text is short enough that no line break is
>> needed.
>>
>> I think we should change `ExtendedTextSourceLabel.getSubset()` to return
>> `this` if the requested subset is identical to the existing instance. This
>> will allow us to use the existing cached `GlyphVector`, and the call to
>> `LineBreakMeasurer.nextLayout()` will trigger text shaping once, rather than
>> twice.
>>
>> In local testing, the test program below ran in ~1250 ms before this
>> optimization, and ran in ~960 ms after the change (a 23% reduction in run
>> time).
>>
>> The following three existing test classes provide good regression test
>> coverage for this change:
>> - test/jdk/java/awt/font/LineBreakMeasurer/LineBreakWithTrackingAuto
>> - test/jdk/java/awt/font/LineBreakMeasurer/TestLineBreakWithFontSub
>> - test/jdk/java/awt/font/LineBreakMeasurer/FRCTest
>>
>>
>> public class LineBreakMeasurerPerfTest {
>>
>> public static void main(String[] args) {
>>
>> float advance = 0;
>> long start = System.currentTimeMillis();
>> AttributedString string = new AttributedString("This is a test.");
>> FontRenderContext frc = new FontRenderContext(new AffineTransform(),
>> true, true);
>>
>> for (int i = 0; i < 100_000; i++) {
>> LineBreakMeasurer measurer = new
>> LineBreakMeasurer(string.getIterator(), frc);
>> TextLayout layout = measurer.nextLayout(999); // large enough to
>> not require break
>> advance = Math.max(advance, layout.getAdvance());
>> }
>>
>> long end = System.currentTimeMillis();
>> System.out.println((end - start) + " ms elapsed (advance: " +
>> advance + ")");
>> }
>>
>> }
>
> If any reviewers have some extra cycles, I'd appreciate a second review on
> this one. Thanks!
@gredler I'm in the process of reviewing it. I can sponsor the PR once done
with testing.
-------------
PR Comment: https://git.openjdk.org/jdk/pull/25193#issuecomment-2902500432
