`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 +
")");
}
}
-------------
Commit messages:
- Avoid double text shaping in some scenarios
Changes: https://git.openjdk.org/jdk/pull/25193/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25193&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8356814
Stats: 8 lines in 1 file changed: 7 ins; 0 del; 1 mod
Patch: https://git.openjdk.org/jdk/pull/25193.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/25193/head:pull/25193
PR: https://git.openjdk.org/jdk/pull/25193
