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LibGfx/OpenType: Load x-height metrics from OS/2 table if available

Before this change we always returned the font's point size as the
x-height which was basically never correct.

We now get it from the OS/2 table (if one with version >= 2 is available
in the file). Otherwise we fall back to using the ascent of the 'x'
glyph. Most fonts appear to have a sufficiently modern OS/2 table.
Andreas Kling 2 years ago
parent
8090adf268
commit
69c33bd4ca
6 changed files with 50 additions and 1 deletions
Unified View Show Diff Stats
  1. 4 0
      Tests/LibWeb/Layout/expected/css-ex-unit.txt
  2. 8 0
      Tests/LibWeb/Layout/input/css-ex-unit.html
  3. 14 0
      Userland/Libraries/LibGfx/Font/OpenType/Font.cpp
  4. 22 0
      Userland/Libraries/LibGfx/Font/OpenType/Tables.h
  5. 1 1
      Userland/Libraries/LibGfx/Font/ScaledFont.cpp
  6. 1 0
      Userland/Libraries/LibGfx/Font/VectorFont.h

+ 4 - 0
Tests/LibWeb/Layout/expected/css-ex-unit.txt
View File 

@@ -0,0 +1,4 @@
 
+Viewport <#document> at (0,0) content-size 800x600 children: not-inline
 
+  BlockContainer <html> at (0,0) content-size 800x177.132812 [BFC] children: not-inline
 
+    BlockContainer <body> at (8,8) content-size 784x161.132812 children: not-inline
 
+      BlockContainer <div> at (8,8) content-size 107.421875x161.132812 children: not-inline

+ 8 - 0
Tests/LibWeb/Layout/input/css-ex-unit.html
View File 

@@ -0,0 +1,8 @@
 
+<!doctype html><style>
 
+div {
 
+    font: 20px SerenitySans;
 
+    width: 10ex;
 
+    height: 15ex;
 
+    background: red;
 
+}
 
+</style><div>

+ 14 - 0
Userland/Libraries/LibGfx/Font/OpenType/Font.cpp
View File 

@@ -574,21 +574,28 @@ Gfx::ScaledFontMetrics Font::metrics([[maybe_unused]] float x_scale, float y_sca
 
     i16 raw_ascender;
 
     i16 raw_ascender;
 
     i16 raw_descender;
 
     i16 raw_descender;
 
     i16 raw_line_gap;
 
     i16 raw_line_gap;
 
+    Optional<i16> x_height;
 
 
 
     if (m_os2.has_value() && m_os2->use_typographic_metrics()) {
 
     if (m_os2.has_value() && m_os2->use_typographic_metrics()) {
 
         raw_ascender = m_os2->typographic_ascender();
 
         raw_ascender = m_os2->typographic_ascender();
 
         raw_descender = m_os2->typographic_descender();
 
         raw_descender = m_os2->typographic_descender();
 
         raw_line_gap = m_os2->typographic_line_gap();
 
         raw_line_gap = m_os2->typographic_line_gap();
 
+        x_height = m_os2->x_height();
 
     } else {
 
     } else {
 
         raw_ascender = m_hhea.ascender();
 
         raw_ascender = m_hhea.ascender();
 
         raw_descender = m_hhea.descender();
 
         raw_descender = m_hhea.descender();
 
         raw_line_gap = m_hhea.line_gap();
 
         raw_line_gap = m_hhea.line_gap();
 
     }
 
     }
 
 
 
+    if (!x_height.has_value()) {
 
+        x_height = glyph_metrics(glyph_id_for_code_point('x'), 1, 1, 1, 1).ascender;
 
+    }
 
+
 
     return Gfx::ScaledFontMetrics {
 
     return Gfx::ScaledFontMetrics {
 
         .ascender = static_cast<float>(raw_ascender) * y_scale,
 
         .ascender = static_cast<float>(raw_ascender) * y_scale,
 
         .descender = -static_cast<float>(raw_descender) * y_scale,
 
         .descender = -static_cast<float>(raw_descender) * y_scale,
 
         .line_gap = static_cast<float>(raw_line_gap) * y_scale,
 
         .line_gap = static_cast<float>(raw_line_gap) * y_scale,
 
+        .x_height = static_cast<float>(x_height.value()) * y_scale,
 
     };
 
     };
 
 }
 
 }
 
 
 
@@ -854,6 +861,13 @@ bool OS2::use_typographic_metrics() const
 
     return header().fs_selection & 0x80;
 
     return header().fs_selection & 0x80;
 
 }
 
 }
 
 
 
+Optional<i16> OS2::x_height() const
 
+{
 
+    if (header().version < 2)
 
+        return {};
 
+    return header_v2().sx_height;
 
+}
 
+
 
 Optional<ReadonlyBytes> Font::font_program() const
 
 Optional<ReadonlyBytes> Font::font_program() const
 
 {
 
 {
 
     if (m_fpgm.has_value())
 
     if (m_fpgm.has_value())

+ 22 - 0
Userland/Libraries/LibGfx/Font/OpenType/Tables.h
View File 

@@ -243,6 +243,8 @@ public:
 
 
 
     bool use_typographic_metrics() const;
 
     bool use_typographic_metrics() const;
 
 
 
+    [[nodiscard]] Optional<i16> x_height() const;
 
+
 
     explicit OS2(ReadonlyBytes slice)
 
     explicit OS2(ReadonlyBytes slice)
 
         : m_slice(slice)
 
         : m_slice(slice)
 
     {
 
     {
 
@@ -282,7 +284,27 @@ private:
 
         BigEndian<u16> us_win_descent;
 
         BigEndian<u16> us_win_descent;
 
     };
 
     };
 
 
 
+    struct Version1 {
 
+        Version0 version0;
 
+        BigEndian<u32> ul_code_page_range1;
 
+        BigEndian<u32> ul_code_page_range2;
 
+    };
 
+
 
+    struct Version2 {
 
+        Version1 version1;
 
+        BigEndian<i16> sx_height;
 
+        BigEndian<i16> s_cap_height;
 
+        BigEndian<u16> us_default_char;
 
+        BigEndian<u16> us_break_char;
 
+        BigEndian<u16> us_max_context;
 
+    };
 
+
 
     Version0 const& header() const { return *bit_cast<Version0 const*>(m_slice.data()); }
 
     Version0 const& header() const { return *bit_cast<Version0 const*>(m_slice.data()); }
 
+    Version2 const& header_v2() const
 
+    {
 
+        VERIFY(header().version >= 2);
 
+        return *bit_cast<Version2 const*>(m_slice.data());
 
+    }
 
 
 
     ReadonlyBytes m_slice;
 
     ReadonlyBytes m_slice;
 
 };
 
 };

+ 1 - 1
Userland/Libraries/LibGfx/Font/ScaledFont.cpp
View File 

@@ -27,7 +27,7 @@ ScaledFont::ScaledFont(NonnullRefPtr<VectorFont> font, float point_width, float
 
 
 
     m_pixel_metrics = Gfx::FontPixelMetrics {
 
     m_pixel_metrics = Gfx::FontPixelMetrics {
 
         .size = (float)pixel_size(),
 
         .size = (float)pixel_size(),
 
-        .x_height = (float)x_height(),
 
+        .x_height = metrics.x_height,
 
         .advance_of_ascii_zero = (float)glyph_width('0'),
 
         .advance_of_ascii_zero = (float)glyph_width('0'),
 
         .glyph_spacing = (float)glyph_spacing(),
 
         .glyph_spacing = (float)glyph_spacing(),
 
         .ascent = metrics.ascender,
 
         .ascent = metrics.ascender,

+ 1 - 0
Userland/Libraries/LibGfx/Font/VectorFont.h
View File 

@@ -17,6 +17,7 @@ struct ScaledFontMetrics {
 
     float ascender { 0 };
 
     float ascender { 0 };
 
     float descender { 0 };
 
     float descender { 0 };
 
     float line_gap { 0 };
 
     float line_gap { 0 };
 
+    float x_height { 0 };
 
 
 
     float height() const
 
     float height() const
 
     {
 
     {

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