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LibGfx: Survive empty simple glyphs with 0 contours

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Some fonts have empty slices for glyphs with 0 contours, even though
the spec requires them to store a 0 for instructionLength as far as
I can tell. But let's not assert on invalid fonts like this, but instead
handle them gracefully.

Supersedes #22570.

Fixes the last two crashes on my 1000-file test set: 0000246.pdf and
0000431.pdf.
This commit is contained in:
Nico Weber 2024-02-26 19:49:31 -05:00 • committed by Andreas Kling
parent cafaaa0e76
commit 75e5ed7aea
1 changed files with 7 additions and 3 deletions
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10
Userland/Libraries/LibGfx/Font/OpenType/Glyf.cpp
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@ -238,6 +238,9 @@ static void get_ttglyph_offsets(ReadonlyBytes slice, u32 num_points, u32 flags_o
ReadonlyBytes Glyf::Glyph::program() const
{
if (m_num_contours == 0)
return {};
auto instructions_start = m_num_contours * 2;
u16 num_instructions = be_u16(m_slice.offset(instructions_start));
return m_slice.slice(instructions_start + 2, num_instructions);
@ -245,10 +248,11 @@ ReadonlyBytes Glyf::Glyph::program() const
void Glyf::Glyph::append_path_impl(Gfx::Path& path, Gfx::AffineTransform const& transform) const
{
if (m_num_contours == 0)
return;
// Get offset for flags, x, and y.
u16 num_points = 0;
if (m_num_contours > 0)
num_points = be_u16(m_slice.offset((m_num_contours - 1) * 2)) + 1;
u16 num_points = be_u16(m_slice.offset((m_num_contours - 1) * 2)) + 1;
u16 num_instructions = be_u16(m_slice.offset(m_num_contours * 2));
u32 flags_offset = m_num_contours * 2 + 2 + num_instructions;
u32 x_offset = 0;