LibGfx/OpenType: Make glyph_width() only fetch the glyph advance

Instead of fetching a generic set of metrics for each glyph, only fetch
the advance when that's all we need.

This is extremely hot in LibWeb text layout, where it makes a nice dent.

Userland/Libraries/LibGfx/Font/OpenType/Font.cpp

@@ -413,6 +413,21 @@ Font::EmbeddedBitmapData Font::embedded_bitmap_data_for_glyph(u32 glyph_id) cons
     return Empty {};
 }
 
+float Font::glyph_advance(u32 glyph_id, float x_scale, float y_scale, float point_width, float point_height) const
+{
+    if (has_color_bitmaps())
+        return glyph_metrics(glyph_id, x_scale, y_scale, point_width, point_height).advance_width;
+
+    if (!m_hmtx.has_value())
+        return 0;
+
+    if (glyph_id >= glyph_count())
+        glyph_id = 0;
+
+    auto horizontal_metrics = m_hmtx->get_glyph_horizontal_metrics(glyph_id);
+    return static_cast<float>(horizontal_metrics.advance_width) * x_scale;
+}
+
 Gfx::ScaledGlyphMetrics Font::glyph_metrics(u32 glyph_id, float x_scale, float y_scale, float point_width, float point_height) const
 {
     auto embedded_bitmap_metrics = embedded_bitmap_data_for_glyph(glyph_id).visit(

Userland/Libraries/LibGfx/Font/OpenType/Font.h

@@ -54,6 +54,7 @@ public:
 
     virtual Gfx::ScaledFontMetrics metrics(float x_scale, float y_scale) const override;
     virtual Gfx::ScaledGlyphMetrics glyph_metrics(u32 glyph_id, float x_scale, float y_scale, float point_width, float point_height) const override;
+    virtual float glyph_advance(u32 glyph_id, float x_scale, float y_scale, float point_width, float point_height) const override;
     virtual float glyphs_horizontal_kerning(u32 left_glyph_id, u32 right_glyph_id, float x_scale) const override;
     virtual RefPtr<Gfx::Bitmap> rasterize_glyph(u32 glyph_id, float x_scale, float y_scale, Gfx::GlyphSubpixelOffset) const override;
     virtual bool append_glyph_path_to(Gfx::Path&, u32 glyph_id, float x_scale, float y_scale) const override;

Userland/Libraries/LibGfx/Font/ScaledFont.cpp

@@ -110,8 +110,7 @@ float ScaledFont::glyph_left_bearing(u32 code_point) const
 float ScaledFont::glyph_width(u32 code_point) const
 {
     auto id = glyph_id_for_code_point(code_point);
-    auto metrics = glyph_metrics(id);
-    return metrics.advance_width;
+    return m_font->glyph_advance(id, m_x_scale, m_y_scale, m_point_width, m_point_height);
 }
 
 template<typename CodePointIterator>

Userland/Libraries/LibGfx/Font/VectorFont.h

@@ -44,6 +44,7 @@ public:
     virtual ~VectorFont();
     virtual ScaledFontMetrics metrics(float x_scale, float y_scale) const = 0;
     virtual ScaledGlyphMetrics glyph_metrics(u32 glyph_id, float x_scale, float y_scale, float point_width, float point_height) const = 0;
+    virtual float glyph_advance(u32 glyph_id, float x_scale, float y_scale, float point_width, float point_height) const = 0;
     virtual float glyphs_horizontal_kerning(u32 left_glyph_id, u32 right_glyph_id, float x_scale) const = 0;
     virtual RefPtr<Gfx::Bitmap> rasterize_glyph(u32 glyph_id, float x_scale, float y_scale, GlyphSubpixelOffset) const = 0;
     virtual bool append_glyph_path_to(Gfx::Path&, u32 glyph_id, float x_scale, float y_scale) const = 0;

Userland/Libraries/LibGfx/Font/WOFF/Font.h

@@ -26,6 +26,7 @@ public:
 
     virtual Gfx::ScaledFontMetrics metrics(float x_scale, float y_scale) const override { return m_input_font->metrics(x_scale, y_scale); }
     virtual Gfx::ScaledGlyphMetrics glyph_metrics(u32 glyph_id, float x_scale, float y_scale, float point_width, float point_height) const override { return m_input_font->glyph_metrics(glyph_id, x_scale, y_scale, point_width, point_height); }
+    virtual float glyph_advance(u32 glyph_id, float x_scale, float y_scale, float point_width, float point_height) const override { return m_input_font->glyph_advance(glyph_id, x_scale, y_scale, point_width, point_height); }
     virtual float glyphs_horizontal_kerning(u32 left_glyph_id, u32 right_glyph_id, float x_scale) const override { return m_input_font->glyphs_horizontal_kerning(left_glyph_id, right_glyph_id, x_scale); }
     virtual RefPtr<Gfx::Bitmap> rasterize_glyph(u32 glyph_id, float x_scale, float y_scale, Gfx::GlyphSubpixelOffset subpixel_offset) const override { return m_input_font->rasterize_glyph(glyph_id, x_scale, y_scale, subpixel_offset); }
     virtual bool append_glyph_path_to(Gfx::Path& path, u32 glyph_id, float x_scale, float y_scale) const override { return m_input_font->append_glyph_path_to(path, glyph_id, x_scale, y_scale); }

Userland/Libraries/LibGfx/Font/WOFF2/Font.h

@@ -27,6 +27,7 @@ public:
 
     virtual Gfx::ScaledFontMetrics metrics(float x_scale, float y_scale) const override { return m_input_font->metrics(x_scale, y_scale); }
     virtual Gfx::ScaledGlyphMetrics glyph_metrics(u32 glyph_id, float x_scale, float y_scale, float point_width, float point_height) const override { return m_input_font->glyph_metrics(glyph_id, x_scale, y_scale, point_width, point_height); }
+    virtual float glyph_advance(u32 glyph_id, float x_scale, float y_scale, float point_width, float point_height) const override { return m_input_font->glyph_advance(glyph_id, x_scale, y_scale, point_width, point_height); }
     virtual float glyphs_horizontal_kerning(u32 left_glyph_id, u32 right_glyph_id, float x_scale) const override { return m_input_font->glyphs_horizontal_kerning(left_glyph_id, right_glyph_id, x_scale); }
     virtual RefPtr<Gfx::Bitmap> rasterize_glyph(u32 glyph_id, float x_scale, float y_scale, Gfx::GlyphSubpixelOffset subpixel_offset) const override
     {