On Fri, 21 Feb 2025 21:13:16 GMT, Daniel Gredler <dgred...@openjdk.org> wrote:
>> When a string contains zero-width characters, `LineBreakMeasurer` calculates >> line breaks incorrectly. >> >> The root cause appears to be that `LineBreakMeasurer` eventually calls into >> `StandardGlyphVector.getGlyphInfo()`, which derives the glyph advances from >> the glyph IDs. However, HarfBuzz's default treatment of zero-width >> characters is to provide the glyph ID of the space character (`U+0020`) >> combined with an artificial zero advance (not the font's space glyph >> advance). Unaware of HarfBuzz's sleight of hand, >> `StandardGlyphVector.getGlyphInfo()` retrieves the actual advances of the >> space glyph (since that was the glyph ID returned) and provides these back >> up the call chain to `LineBreakMeasurer` et al. >> >> I think the correct fix is to use `hb_buffer_set_invisible_glyph` to >> register `0xFFFF` as the invisible glyph ID with HarfBuzz (matching >> `CharToGlyphMapper.INVISIBLE_GLYPH_ID`). >> >> I haven't seen any unwanted side effects, but there is a risk, since this is >> changing the global HarfBuzz configuration. >> >> For more information on HarfBuzz's behavior in this area, see: >> https://harfbuzz.github.io/setting-buffer-properties.html > > Daniel Gredler has updated the pull request incrementally with one additional > commit since the last revision: > > Update copyright year I am seeing an existing test fail on macOS with this change java/awt/font/GlyphVector/NLGlyphTest.java java NLGlyphTest Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0 at java.desktop/sun.font.StandardGlyphVector.getGlyphCode(StandardGlyphVector.java:311) at NLGlyphTest.main(NLGlyphTest.java:46) I don't know why, but it seems like this char[] chs = { '\n' }; GlyphVector lgv = font.layoutGlyphVector(frc, chs, 0, 1, 0); results in a GV with zero glyphs ------------- PR Comment: https://git.openjdk.org/jdk/pull/23603#issuecomment-2705084008
