From 850b4a03e6e5c0478c3c63559abddd8f714b6ac4 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Mon, 16 Jan 2023 09:26:01 +0100
Subject: [PATCH] LibGfx: Cache font pixel metrics in ScaledFont

Instead of recomputing the pixel metrics over and over, we can just
cache them with the font and avoid a bunch of expensive computation.
---
 Userland/Libraries/LibGfx/Font/ScaledFont.cpp | 34 +++++++++++++------
 Userland/Libraries/LibGfx/Font/ScaledFont.h   | 13 ++-----
 2 files changed, 26 insertions(+), 21 deletions(-)

diff --git a/Userland/Libraries/LibGfx/Font/ScaledFont.cpp b/Userland/Libraries/LibGfx/Font/ScaledFont.cpp
index 70437e9040..5e4040c235 100644
--- a/Userland/Libraries/LibGfx/Font/ScaledFont.cpp
+++ b/Userland/Libraries/LibGfx/Font/ScaledFont.cpp
@@ -10,6 +10,28 @@
 
 namespace Gfx {
 
+ScaledFont::ScaledFont(NonnullRefPtr<VectorFont> font, float point_width, float point_height, unsigned dpi_x, unsigned dpi_y)
+    : m_font(move(font))
+    , m_point_width(point_width)
+    , m_point_height(point_height)
+{
+    float units_per_em = m_font->units_per_em();
+    m_x_scale = (point_width * dpi_x) / (POINTS_PER_INCH * units_per_em);
+    m_y_scale = (point_height * dpi_y) / (POINTS_PER_INCH * units_per_em);
+
+    auto metrics = m_font->metrics(m_x_scale, m_y_scale);
+
+    m_pixel_metrics = 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,
+    };
+}
+
 float ScaledFont::width(StringView view) const { return unicode_view_width(Utf8View(view)); }
 float ScaledFont::width(Utf8View const& view) const { return unicode_view_width(view); }
 float ScaledFont::width(Utf32View const& view) const { return unicode_view_width(view); }
@@ -103,17 +125,7 @@ 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,
-    };
+    return m_pixel_metrics;
 }
 
 }
diff --git a/Userland/Libraries/LibGfx/Font/ScaledFont.h b/Userland/Libraries/LibGfx/Font/ScaledFont.h
index 3cc5705e25..3c47cc498e 100644
--- a/Userland/Libraries/LibGfx/Font/ScaledFont.h
+++ b/Userland/Libraries/LibGfx/Font/ScaledFont.h
@@ -23,17 +23,9 @@ struct GlyphIndexWithSubpixelOffset {
     bool operator==(GlyphIndexWithSubpixelOffset const&) const = default;
 };
 
-class ScaledFont : public Gfx::Font {
+class ScaledFont final : public Gfx::Font {
 public:
-    ScaledFont(NonnullRefPtr<VectorFont> font, float point_width, float point_height, unsigned dpi_x = DEFAULT_DPI, unsigned dpi_y = DEFAULT_DPI)
-        : m_font(move(font))
-        , m_point_width(point_width)
-        , m_point_height(point_height)
-    {
-        float units_per_em = m_font->units_per_em();
-        m_x_scale = (point_width * dpi_x) / (POINTS_PER_INCH * units_per_em);
-        m_y_scale = (point_height * dpi_y) / (POINTS_PER_INCH * units_per_em);
-    }
+    ScaledFont(NonnullRefPtr<VectorFont>, float point_width, float point_height, unsigned dpi_x = DEFAULT_DPI, unsigned dpi_y = DEFAULT_DPI);
     u32 glyph_id_for_code_point(u32 code_point) const { return m_font->glyph_id_for_code_point(code_point); }
     ScaledFontMetrics metrics() const { return m_font->metrics(m_x_scale, m_y_scale); }
     ScaledGlyphMetrics glyph_metrics(u32 glyph_id) const { return m_font->glyph_metrics(glyph_id, m_x_scale, m_y_scale); }
@@ -81,6 +73,7 @@ private:
     float m_point_width { 0.0f };
     float m_point_height { 0.0f };
     mutable HashMap<GlyphIndexWithSubpixelOffset, RefPtr<Gfx::Bitmap>> m_cached_glyph_bitmaps;
+    Gfx::FontPixelMetrics m_pixel_metrics;
 
     template<typename T>
     float unicode_view_width(T const& view) const;