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LibGfx/OpenType: Cache kerning values for faster text layout

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The Font class now remembers the results of kerning lookups in a
HashMap. This fixes an issue where text-heavy UI (like WidgetGallery)
would lag when using a UI font with kerning data.
This commit is contained in:
Andreas Kling 2023-05-07 07:18:43 +02:00
parent 677386bfaa
commit 97f0106edd
2 changed files with 23 additions and 6 deletions
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27
Userland/Libraries/LibGfx/Font/OpenType/Font.cpp
View file

@ -676,15 +676,30 @@ Gfx::ScaledGlyphMetrics Font::glyph_metrics(u32 glyph_id, float x_scale, float y
float Font::glyphs_horizontal_kerning(u32 left_glyph_id, u32 right_glyph_id, float x_scale) const
{
if (m_gpos.has_value()) {
auto kerning = m_gpos->glyph_kerning(left_glyph_id, right_glyph_id);
if (kerning.has_value())
return kerning.value() * x_scale;
if (!m_gpos.has_value() && !m_kern.has_value())
return 0.0f;
// NOTE: OpenType glyph IDs are 16-bit, so this is safe.
auto cache_key = (left_glyph_id << 16) | right_glyph_id;
if (auto it = m_kerning_cache.find(cache_key); it != m_kerning_cache.end()) {
return it->value * x_scale;
}
if (m_kern.has_value())
return m_kern->get_glyph_kerning(left_glyph_id, right_glyph_id) * x_scale;
if (m_gpos.has_value()) {
auto kerning = m_gpos->glyph_kerning(left_glyph_id, right_glyph_id);
if (kerning.has_value()) {
m_kerning_cache.set(cache_key, kerning.value());
return kerning.value() * x_scale;
}
}
if (m_kern.has_value()) {
auto kerning = m_kern->get_glyph_kerning(left_glyph_id, right_glyph_id) * x_scale;
m_kerning_cache.set(cache_key, kerning);
return kerning;
}
m_kerning_cache.set(cache_key, 0);
return 0.0f;
}

2
Userland/Libraries/LibGfx/Font/OpenType/Font.h
View file

@ -141,6 +141,8 @@ private:
mutable HashMap<size_t, NonnullOwnPtr<GlyphPage>> m_glyph_pages;
mutable HashMap<u32, i16> m_kerning_cache;
GlyphPage const& glyph_page(size_t page_index) const;
void populate_glyph_page(GlyphPage&, size_t page_index) const;
};