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 Interesting, I've been testing on Linux. I'll break out the Mac to see what's going on. ------------- PR Comment: https://git.openjdk.org/jdk/pull/23603#issuecomment-2657968332
