LibGfx: Add ascent, descent and line gap to FontPixelMetrics

These are the main values we need in LibWeb to perform inline layout.

Userland/Libraries/LibGfx/BitmapFont.cpp

@@ -379,6 +379,9 @@ FontPixelMetrics BitmapFont::pixel_metrics() const
         .x_height = (float)x_height(),
         .advance_of_ascii_zero = (float)glyph_width('0'),
         .glyph_spacing = (float)glyph_spacing(),
+        .ascent = (float)m_baseline,
+        .descent = (float)(m_glyph_height - m_baseline),
+        .line_gap = (float)pixel_size() * 0.4f, // FIXME: Do something nicer here.
     };
 }
 

Userland/Libraries/LibGfx/Font.h

@@ -91,6 +91,17 @@ struct FontPixelMetrics {
     float x_height { 0 };
     float advance_of_ascii_zero { 0 };
     float glyph_spacing { 0 };
+
+    // Number of pixels the font extends above the baseline.
+    float ascent { 0 };
+
+    // Number of pixels the font descends below the baseline.
+    float descent { 0 };
+
+    // Line gap specified by font.
+    float line_gap { 0 };
+
+    float line_spacing() const { return roundf(ascent) + roundf(descent) + roundf(line_gap); }
 };
 
 class Font : public RefCounted<Font> {

Userland/Libraries/LibGfx/TrueTypeFont/Font.cpp

@@ -526,17 +526,16 @@ ErrorOr<NonnullRefPtr<Font>> Font::try_load_from_offset(ReadonlyBytes buffer, u3
     return adopt_ref(*new Font(move(buffer), move(head), move(name), move(hhea), move(maxp), move(hmtx), move(cmap), move(loca), move(glyf), move(os2), move(kern)));
 }
 
-ScaledFontMetrics Font::metrics(float x_scale, float y_scale) const
+ScaledFontMetrics Font::metrics([[maybe_unused]] float x_scale, float y_scale) const
 {
     auto ascender = m_hhea.ascender() * y_scale;
     auto descender = m_hhea.descender() * y_scale;
     auto line_gap = m_hhea.line_gap() * y_scale;
-    auto advance_width_max = m_hhea.advance_width_max() * x_scale;
+
     return ScaledFontMetrics {
-        .ascender = (int)roundf(ascender),
-        .descender = (int)roundf(descender),
-        .line_gap = (int)roundf(line_gap),
-        .advance_width_max = (int)roundf(advance_width_max),
+        .ascender = ascender,
+        .descender = descender,
+        .line_gap = line_gap,
     };
 }
 
@@ -726,11 +725,16 @@ u8 ScaledFont::glyph_fixed_width() const
 
 Gfx::FontPixelMetrics ScaledFont::pixel_metrics() const
 {
+    auto metrics = m_font->metrics(m_x_scale, m_y_scale);
+
     return Gfx::FontPixelMetrics {
         .size = (float)pixel_size(),
         .x_height = (float)x_height(),
         .advance_of_ascii_zero = (float)glyph_width('0'),
         .glyph_spacing = (float)glyph_spacing(),
+        .ascent = metrics.ascender,
+        .descent = -metrics.descender,
+        .line_gap = metrics.line_gap,
     };
 }
 

Userland/Libraries/LibGfx/TrueTypeFont/Font.h

@@ -23,10 +23,9 @@
 namespace TTF {
 
 struct ScaledFontMetrics {
-    int ascender;
-    int descender;
-    int line_gap;
-    int advance_width_max;
+    float ascender { 0 };
+    float descender { 0 };
+    float line_gap { 0 };
 
     int height() const
     {