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LibGfx: Don't render OpenType glyphs that have no outline

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The spec tells us that for glyph offsets in the "loca" table, if an
offset appears twice in a row, the index of the first one refers to a
glyph without an outline (such as the space character). We didn't check
for this, which would cause us to render a glyph outline where there
should have been nothing.
This commit is contained in:
Julian Offenhäuser 2023-03-28 14:51:51 +02:00 • committed by Andreas Kling
parent a28aba7663
commit 5ccb240945
2 changed files with 11 additions and 3 deletions
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11
Userland/Libraries/LibGfx/Font/OpenType/Font.cpp
View file

@ -699,8 +699,15 @@ RefPtr<Gfx::Bitmap> Font::rasterize_glyph(u32 glyph_id, float x_scale, float y_s
if (glyph_id >= glyph_count()) { if (glyph_id >= glyph_count()) {
glyph_id = 0; glyph_id = 0;
} }
auto glyph_offset = m_loca->get_glyph_offset(glyph_id);
auto glyph = m_glyf->glyph(glyph_offset); auto glyph_offset0 = m_loca->get_glyph_offset(glyph_id);
auto glyph_offset1 = m_loca->get_glyph_offset(glyph_id + 1);
// If a glyph has no outline, then loca[n] = loca [n+1].
if (glyph_offset0 == glyph_offset1)
return nullptr;
auto glyph = m_glyf->glyph(glyph_offset0);
i16 ascender = 0; i16 ascender = 0;
i16 descender = 0; i16 descender = 0;

3
Userland/Libraries/LibGfx/Font/OpenType/Glyf.cpp
View file

@ -208,7 +208,8 @@ Optional<Loca> Loca::from_slice(ReadonlyBytes slice, u32 num_glyphs, IndexToLocF
u32 Loca::get_glyph_offset(u32 glyph_id) const u32 Loca::get_glyph_offset(u32 glyph_id) const
{ {
VERIFY(glyph_id < m_num_glyphs); // NOTE: The value of n is numGlyphs + 1.
VERIFY(glyph_id <= m_num_glyphs);
switch (m_index_to_loc_format) { switch (m_index_to_loc_format) {
case IndexToLocFormat::Offset16: case IndexToLocFormat::Offset16:
return ((u32)be_u16(m_slice.offset_pointer(glyph_id * 2))) * 2; return ((u32)be_u16(m_slice.offset_pointer(glyph_id * 2))) * 2;