LibGfx+FontEditor+Fonts: Add "mean line" value to all fonts

The main inspiration behind this was to have a correct ex CSS unit.
The mean line is based off what it shows in the CSS Values and Units
Level 4 specification, section 6.1.1.

https://www.w3.org/TR/css-values-4/#font-relative-lengths

Applications/FontEditor/FontEditor.cpp

@@ -121,7 +121,7 @@ FontEditorWidget::FontEditorWidget(const String& path, RefPtr<Gfx::Font>&& edite
     font_metadata_group_box.set_layout<GUI::VerticalBoxLayout>();
     font_metadata_group_box.layout()->set_margins({ 5, 15, 5, 5 });
     font_metadata_group_box.set_size_policy(GUI::SizePolicy::Fill, GUI::SizePolicy::Fixed);
-    font_metadata_group_box.set_preferred_size(0, 165);
+    font_metadata_group_box.set_preferred_size(0, 195);
     font_metadata_group_box.set_title("Font metadata");
 
     //// Name Row
@@ -212,12 +212,31 @@ FontEditorWidget::FontEditorWidget(const String& path, RefPtr<Gfx::Font>&& edite
     baseline_label.set_text("Baseline:");
 
     auto& baseline_spinbox = baseline_container.add<GUI::SpinBox>();
-    baseline_spinbox.set_size_policy(GUI::SizePolicy::Fixed, GUI::SizePolicy::Fill);
+    baseline_spinbox.set_size_policy(GUI::SizePolicy::Fill, GUI::SizePolicy::Fill);
     baseline_spinbox.set_preferred_size(100, 0);
     baseline_spinbox.set_min(0);
     baseline_spinbox.set_max(m_edited_font->glyph_height() - 1);
     baseline_spinbox.set_value(m_edited_font->baseline());
 
+    //// Mean line Row
+    auto& mean_line_container = font_metadata_group_box.add<GUI::Widget>();
+    mean_line_container.set_layout<GUI::HorizontalBoxLayout>();
+    mean_line_container.set_size_policy(GUI::SizePolicy::Fill, GUI::SizePolicy::Fixed);
+    mean_line_container.set_preferred_size(0, 22);
+
+    auto& mean_line_label = mean_line_container.add<GUI::Label>();
+    mean_line_label.set_size_policy(GUI::SizePolicy::Fixed, GUI::SizePolicy::Fill);
+    mean_line_label.set_preferred_size(100, 0);
+    mean_line_label.set_text_alignment(Gfx::TextAlignment::CenterLeft);
+    mean_line_label.set_text("Mean Line:");
+
+    auto& mean_line_spinbox = mean_line_container.add<GUI::SpinBox>();
+    mean_line_spinbox.set_size_policy(GUI::SizePolicy::Fill, GUI::SizePolicy::Fill);
+    mean_line_spinbox.set_preferred_size(100, 0);
+    mean_line_spinbox.set_min(0);
+    mean_line_spinbox.set_max(m_edited_font->glyph_height() - 1);
+    mean_line_spinbox.set_value(m_edited_font->mean_line());
+
     //// Fixed checkbox Row
     auto& fixed_width_checkbox = font_metadata_group_box.add<GUI::CheckBox>();
     fixed_width_checkbox.set_size_policy(GUI::SizePolicy::Fill, GUI::SizePolicy::Fixed);
@@ -259,7 +278,7 @@ FontEditorWidget::FontEditorWidget(const String& path, RefPtr<Gfx::Font>&& edite
         right_site_width = max(right_site_width, m_glyph_map_widget->preferred_width());
 
         m_preferred_width = m_glyph_editor_widget->width() + right_site_width + 20;
-        m_preferred_height = m_glyph_map_widget->relative_rect().height() + 2 * m_edited_font->glyph_height() + 270;
+        m_preferred_height = m_glyph_map_widget->relative_rect().height() + 2 * m_edited_font->glyph_height() + 300;
     };
 
     m_glyph_editor_widget->on_glyph_altered = [this, update_demo](u8 glyph) {
@@ -308,6 +327,12 @@ FontEditorWidget::FontEditorWidget(const String& path, RefPtr<Gfx::Font>&& edite
         update_demo();
     };
 
+    mean_line_spinbox.on_change = [this, update_demo](int value) {
+        m_edited_font->set_mean_line(value);
+        m_glyph_editor_widget->update();
+        update_demo();
+    };
+
     // init widget
     calculate_prefed_sizes();
     m_glyph_map_widget->set_selected_glyph('A');

Applications/FontEditor/GlyphEditorWidget.cpp

@@ -59,7 +59,8 @@ void GlyphEditorWidget::paint_event(GUI::PaintEvent& event)
 
     painter.translate(-1, -1);
     for (int y = 1; y < font().glyph_height(); ++y) {
-        bool bold_line = (y - 1) == font().baseline();
+        int y_below = y - 1;
+        bool bold_line = y_below == font().baseline() || y_below == font().mean_line();
         painter.draw_line({ 0, y * m_scale }, { font().max_glyph_width() * m_scale, y * m_scale }, palette().threed_shadow2(), bold_line ? 2 : 1);
     }
 

Libraries/LibGfx/Font.cpp

@@ -52,7 +52,8 @@ struct [[gnu::packed]] FontFileHeader
     u8 is_variable_width;
     u8 glyph_spacing;
     u8 baseline;
-    u8 unused[4];
+    u8 mean_line;
+    u8 unused[3];
     char name[64];
 };
 
@@ -111,7 +112,7 @@ NonnullRefPtr<Font> Font::clone() const
         memcpy(new_widths, m_glyph_widths, m_glyph_count);
     else
         memset(new_widths, m_glyph_width, m_glyph_count);
-    return adopt(*new Font(m_name, new_rows, new_widths, m_fixed_width, m_glyph_width, m_glyph_height, m_glyph_spacing, m_type, m_baseline));
+    return adopt(*new Font(m_name, new_rows, new_widths, m_fixed_width, m_glyph_width, m_glyph_height, m_glyph_spacing, m_type, m_baseline, m_mean_line));
 }
 
 NonnullRefPtr<Font> Font::create(u8 glyph_height, u8 glyph_width, bool fixed, FontTypes type)
@@ -123,10 +124,10 @@ NonnullRefPtr<Font> Font::create(u8 glyph_height, u8 glyph_width, bool fixed, Fo
     memset(new_rows, 0, bytes_per_glyph * count);
     auto* new_widths = static_cast<u8*>(malloc(count));
     memset(new_widths, glyph_width, count);
-    return adopt(*new Font("Untitled", new_rows, new_widths, fixed, glyph_width, glyph_height, 1, type, 0));
+    return adopt(*new Font("Untitled", new_rows, new_widths, fixed, glyph_width, glyph_height, 1, type, 0, 0));
 }
 
-Font::Font(const StringView& name, unsigned* rows, u8* widths, bool is_fixed_width, u8 glyph_width, u8 glyph_height, u8 glyph_spacing, FontTypes type, u8 baseline)
+Font::Font(const StringView& name, unsigned* rows, u8* widths, bool is_fixed_width, u8 glyph_width, u8 glyph_height, u8 glyph_spacing, FontTypes type, u8 baseline, u8 mean_line)
     : m_name(name)
     , m_type(type)
     , m_rows(rows)
@@ -137,10 +138,10 @@ Font::Font(const StringView& name, unsigned* rows, u8* widths, bool is_fixed_wid
     , m_max_glyph_width(glyph_width)
     , m_glyph_spacing(glyph_spacing)
     , m_baseline(baseline)
+    , m_mean_line(mean_line)
     , m_fixed_width(is_fixed_width)
 {
-    // FIXME: This is just a dumb guess. It would be cool to know the actual x-height of the font!
-    m_x_height = glyph_height / 2;
+    update_x_height();
 
     m_glyph_count = glyph_count_by_type(m_type);
 
@@ -189,7 +190,7 @@ RefPtr<Font> Font::load_from_memory(const u8* data)
     u8* widths = nullptr;
     if (header.is_variable_width)
         widths = (u8*)(rows) + count * bytes_per_glyph;
-    return adopt(*new Font(String(header.name), rows, widths, !header.is_variable_width, header.glyph_width, header.glyph_height, header.glyph_spacing, type, header.baseline));
+    return adopt(*new Font(String(header.name), rows, widths, !header.is_variable_width, header.glyph_width, header.glyph_height, header.glyph_spacing, type, header.baseline, header.mean_line));
 }
 
 size_t Font::glyph_count_by_type(FontTypes type)
@@ -227,6 +228,7 @@ bool Font::write_to_file(const StringView& path)
     header.glyph_height = m_glyph_height;
     header.type = m_type;
     header.baseline = m_baseline;
+    header.mean_line = m_mean_line;
     header.is_variable_width = !m_fixed_width;
     header.glyph_spacing = m_glyph_spacing;
     memcpy(header.name, m_name.characters(), min(m_name.length(), (size_t)63));

Libraries/LibGfx/Font.h

@@ -101,7 +101,18 @@ public:
     u8 glyph_fixed_width() const { return m_glyph_width; }
 
     u8 baseline() const { return m_baseline; }
-    void set_baseline(u8 baseline) { m_baseline = baseline; }
+    void set_baseline(u8 baseline)
+    {
+        m_baseline = baseline;
+        update_x_height();
+    }
+
+    u8 mean_line() const { return m_mean_line; }
+    void set_mean_line(u8 mean_line)
+    {
+        m_mean_line = mean_line;
+        update_x_height();
+    }
 
     int width(const StringView&) const;
     int width(const Utf8View&) const;
@@ -132,11 +143,13 @@ public:
     void set_type(FontTypes type);
 
 private:
-    Font(const StringView& name, unsigned* rows, u8* widths, bool is_fixed_width, u8 glyph_width, u8 glyph_height, u8 glyph_spacing, FontTypes type, u8 baseline);
+    Font(const StringView& name, unsigned* rows, u8* widths, bool is_fixed_width, u8 glyph_width, u8 glyph_height, u8 glyph_spacing, FontTypes type, u8 baseline, u8 mean_line);
 
     static RefPtr<Font> load_from_memory(const u8*);
     static size_t glyph_count_by_type(FontTypes type);
 
+    void update_x_height() { m_x_height = m_mean_line - m_baseline; };
+
     void set_family_fonts();
     RefPtr<Font> m_bold_family_font;
 
@@ -155,6 +168,7 @@ private:
     u8 m_max_glyph_width { 0 };
     u8 m_glyph_spacing { 0 };
     u8 m_baseline { 0 };
+    u8 m_mean_line { 0 };
 
     bool m_fixed_width { false };
     bool m_boldface { false };