LibGfx: Add ability to request glyphs at subpixel offsets to fonts

This adds the option to pass a subpixel offset when fetching a glyph
from a font, this offset is currently snapped to thirds of a pixel
(i.e. 0, 0.33, 0.66). This is then used when rasterizing the glyph,
which is then cached like usual.

Note that when using subpixel offsets you're trading a bit of space
for accuracy. With the current third of a pixel offsets you can end
up with up to 9 bitmaps per glyph.

1 files changed, 23 insertions, 2 deletions

diff --git a/Userland/Libraries/LibGfx/Font/ScaledFont.h b/Userland/Libraries/LibGfx/Font/ScaledFont.h
index 15d3fa7d40..e346c7b581 100644
--- a/Userland/Libraries/LibGfx/Font/ScaledFont.h
+++ b/Userland/Libraries/LibGfx/Font/ScaledFont.h
@@ -16,6 +16,13 @@
 
 namespace Gfx {
 
+struct GlyphIndexWithSubpixelOffset {
+    u32 glyph_id;
+    GlyphSubpixelOffset subpixel_offset;
+
+    bool operator==(GlyphIndexWithSubpixelOffset const&) const = default;
+};
+
 class ScaledFont : public Gfx::Font {
 public:
     ScaledFont(NonnullRefPtr<VectorFont> font, float point_width, float point_height, unsigned dpi_x = DEFAULT_DPI, unsigned dpi_y = DEFAULT_DPI)
@@ -30,7 +37,7 @@ public:
     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); }
-    RefPtr<Gfx::Bitmap> rasterize_glyph(u32 glyph_id) const;
+    RefPtr<Gfx::Bitmap> rasterize_glyph(u32 glyph_id, GlyphSubpixelOffset) const;
 
     // ^Gfx::Font
     virtual NonnullRefPtr<Font> clone() const override { return MUST(try_clone()); } // FIXME: clone() should not need to be implemented
@@ -42,6 +49,8 @@ public:
     virtual u8 slope() const override { return m_font->slope(); }
     virtual u16 weight() const override { return m_font->weight(); }
     virtual Gfx::Glyph glyph(u32 code_point) const override;
+    virtual float glyph_left_bearing(u32 code_point) const override;
+    virtual Glyph glyph(u32 code_point, GlyphSubpixelOffset) const override;
     virtual bool contains_glyph(u32 code_point) const override { return m_font->glyph_id_for_code_point(code_point) > 0; }
     virtual float glyph_width(u32 code_point) const override;
     virtual float glyph_or_emoji_width(u32 code_point) const override;
@@ -72,10 +81,22 @@ private:
     float m_y_scale { 0.0f };
     float m_point_width { 0.0f };
     float m_point_height { 0.0f };
-    mutable HashMap<u32, RefPtr<Gfx::Bitmap>> m_cached_glyph_bitmaps;
+    mutable HashMap<GlyphIndexWithSubpixelOffset, RefPtr<Gfx::Bitmap>> m_cached_glyph_bitmaps;
 
     template<typename T>
     float unicode_view_width(T const& view) const;
 };
 
 }
+
+namespace AK {
+
+template<>
+struct Traits<Gfx::GlyphIndexWithSubpixelOffset> : public GenericTraits<Gfx::GlyphIndexWithSubpixelOffset> {
+    static unsigned hash(Gfx::GlyphIndexWithSubpixelOffset const& index)
+    {
+        return pair_int_hash(index.glyph_id, (index.subpixel_offset.x << 8) | index.subpixel_offset.y);
+    }
+};
+
+}