On Wed, 12 Feb 2025 23:53:43 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 This pull request has now been integrated. Changeset: 7fc776e2 Author: Daniel Gredler <dgred...@openjdk.org> Committer: Phil Race <p...@openjdk.org> URL: https://git.openjdk.org/jdk/commit/7fc776e2ace920a3b1b319c021e6d3d440305b5e Stats: 23 lines in 6 files changed: 13 ins; 1 del; 9 mod 8270265: LineBreakMeasurer calculates incorrect line breaks with zero-width characters Reviewed-by: achung, prr ------------- PR: https://git.openjdk.org/jdk/pull/23603
