tdf#148330 fix vertical offset for DFKai-SB (ukai.ttf).

DFKai-SB (ukai.ttf) is a built-in font under tradtional Chinese
Windows. The font is very common, especially for official documents.
It is one of the so-called tricky fonts in FreeType[1].

DFKai-SB has incorrect extent in the glyf table[2]. It results in
incorrect glyph positions in vertical writing.

FreeType recalculates the extents based on the
glyph outline, but LibreOffice uses Harfbuzz with
built-in ot font functions instead of ft (FreeType).

This patch decides if the fix is necessary by
checking the family name of the font and the y-offset
value, and recaculates the glyph offset based on glyph
height and top bearing obtained from the glyph bound rect.

[1]https://freetype.org/freetype2/docs/reference/ft2-base_interface.html#ft_face_flag_tricky
[2]https://github.com/harfbuzz/harfbuzz/issues/3521

Change-Id: If632dd38c462c229837e1efb5446e2142f8f0639
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/132511
Tested-by: Jenkins
Reviewed-by: Mark Hung <marklh9@gmail.com>

0 files changed, 0 insertions, 0 deletions