LibGfx: Implement new antialiased filled path rasterizer

This is an implementation of the scanline edge-flag algorithm for
antialiased path filling described here:
https://mlab.taik.fi/~kkallio/antialiasing/EdgeFlagAA.pdf

The initial implementation does not try to implement every possible
optimization in favour of keeping things simple. However, it does
support:

   - Both evenodd and nonzero fill rules
   - Applying paint styles/gradients
   - A range of samples per pixel (8, 16, 32)
   - Very nice antialiasing :^)

This replaces the previous path filling code, that only really applied
antialiasing in the x-axis.

There's some very nice improvements around the web with this change,
especially for small icons. Strokes are still a bit wonky, as they don't
yet use this rasterizer, but I think it should be possible to convert
them to do so.

6 files changed, 536 insertions, 324 deletions

diff --git a/Userland/Libraries/LibGfx/AntiAliasingPainter.cpp b/Userland/Libraries/LibGfx/AntiAliasingPainter.cpp
index 28e6695e16..684784f2ea 100644
--- a/Userland/Libraries/LibGfx/AntiAliasingPainter.cpp
+++ b/Userland/Libraries/LibGfx/AntiAliasingPainter.cpp
@@ -207,19 +207,6 @@ void AntiAliasingPainter::draw_line(FloatPoint actual_from, FloatPoint actual_to
     draw_anti_aliased_line<FixmeEnableHacksForBetterPathPainting::No>(actual_from, actual_to, color, thickness, style, alternate_color, line_length_mode);
 }
 
-// FIXME: In the fill_paths() m_transform.translation() throws away any other transforms
-// this currently does not matter -- but may in future.
-
-void AntiAliasingPainter::fill_path(Path const& path, Color color, Painter::WindingRule rule)
-{
-    m_underlying_painter.antialiased_fill_path(path, color, rule, m_transform.translation());
-}
-
-void AntiAliasingPainter::fill_path(Path const& path, PaintStyle const& paint_style, Painter::WindingRule rule)
-{
-    m_underlying_painter.antialiased_fill_path(path, paint_style, rule, m_transform.translation());
-}
-
 void AntiAliasingPainter::stroke_path(Path const& path, Color color, float thickness)
 {
     FloatPoint cursor;
diff --git a/Userland/Libraries/LibGfx/CMakeLists.txt b/Userland/Libraries/LibGfx/CMakeLists.txt
index ab64783da7..30193191e3 100644
--- a/Userland/Libraries/LibGfx/CMakeLists.txt
+++ b/Userland/Libraries/LibGfx/CMakeLists.txt
@@ -8,7 +8,7 @@ set(SOURCES
     Color.cpp
     CursorParams.cpp
     DeltaE.cpp
-    FillPathImplementation.cpp
+    EdgeFlagPathRasterizer.cpp
     Filters/ColorBlindnessFilter.cpp
     Filters/FastBoxBlurFilter.cpp
     Filters/LumaFilter.cpp
diff --git a/Userland/Libraries/LibGfx/EdgeFlagPathRasterizer.cpp b/Userland/Libraries/LibGfx/EdgeFlagPathRasterizer.cpp
new file mode 100644
index 0000000000..488e469f82
--- /dev/null
+++ b/Userland/Libraries/LibGfx/EdgeFlagPathRasterizer.cpp
@@ -0,0 +1,345 @@
+/*
+ * Copyright (c) 2023, MacDue <macdue@dueutil.tech>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Array.h>
+#include <AK/IntegralMath.h>
+#include <AK/Types.h>
+#include <LibGfx/AntiAliasingPainter.h>
+#include <LibGfx/EdgeFlagPathRasterizer.h>
+
+#if defined(AK_COMPILER_GCC)
+#    pragma GCC optimize("O3")
+#endif
+
+// This a pretty naive implementation of edge-flag scanline AA.
+// The paper lists many possible optimizations, maybe implement one? (FIXME!)
+// https://mlab.taik.fi/~kkallio/antialiasing/EdgeFlagAA.pdf
+// This currently implements:
+//      - The scanline buffer optimization (only allocate one scanline)
+// Possible other optimizations according to the paper:
+//      - Using fixed point numbers
+//      - Edge tracking
+//      - Mask tracking
+//      - Loop unrolling (compilers might handle this better now, the paper is from 2007)
+// Optimizations I think we could add:
+//      - Using fast_u32_fills() for runs of solid colors
+//      - Clipping the plotted edges earlier
+
+namespace Gfx {
+
+static Vector<Detail::Edge> prepare_edges(ReadonlySpan<Path::SplitLineSegment> lines, unsigned samples_per_pixel, FloatPoint origin)
+{
+    // FIXME: split_lines() gives similar information, but the form it's in is not that useful (and is const anyway).
+    Vector<Detail::Edge> edges;
+    edges.ensure_capacity(lines.size());
+
+    for (auto& line : lines) {
+        auto p0 = line.from - origin;
+        auto p1 = line.to - origin;
+
+        p0.scale_by(1, samples_per_pixel);
+        p1.scale_by(1, samples_per_pixel);
+
+        i8 winding = -1;
+        if (p0.y() > p1.y()) {
+            swap(p0, p1);
+        } else {
+            winding = 1;
+        }
+
+        if (p0.y() == p1.y())
+            continue;
+
+        auto dx = p1.x() - p0.x();
+        auto dy = p1.y() - p0.y();
+        float dxdy = float(dx) / dy;
+        float x = p0.x();
+        edges.unchecked_append(Detail::Edge {
+            x,
+            static_cast<int>(p0.y()),
+            static_cast<int>(p1.y()),
+            dxdy,
+            winding,
+            nullptr });
+    }
+    return edges;
+}
+
+template<unsigned SamplesPerPixel>
+EdgeFlagPathRasterizer<SamplesPerPixel>::EdgeFlagPathRasterizer(IntSize size)
+    : m_size(size.width() + 1, size.height() + 1)
+{
+    m_scanline.resize(m_size.width());
+    m_edge_table.resize(m_size.height());
+}
+
+template<unsigned SamplesPerPixel>
+void EdgeFlagPathRasterizer<SamplesPerPixel>::fill(Painter& painter, Path const& path, Color color, Painter::WindingRule winding_rule, FloatPoint offset)
+{
+    fill_internal(painter, path, color, winding_rule, offset);
+}
+
+template<unsigned SamplesPerPixel>
+void EdgeFlagPathRasterizer<SamplesPerPixel>::fill(Painter& painter, Path const& path, PaintStyle const& style, Painter::WindingRule winding_rule, FloatPoint offset)
+{
+    style.paint(enclosing_int_rect(path.bounding_box()), [&](PaintStyle::SamplerFunction sampler) {
+        fill_internal(painter, path, move(sampler), winding_rule, offset);
+    });
+}
+
+template<unsigned SamplesPerPixel>
+void EdgeFlagPathRasterizer<SamplesPerPixel>::fill_internal(Painter& painter, Path const& path, auto color_or_function, Painter::WindingRule winding_rule, FloatPoint offset)
+{
+    // FIXME: Figure out how painter scaling works here...
+    VERIFY(painter.scale() == 1);
+
+    auto bounding_box = enclosing_int_rect(path.bounding_box().translated(offset));
+    auto dest_rect = bounding_box.translated(painter.translation());
+    auto origin = bounding_box.top_left().to_type<float>() - offset;
+    m_blit_origin = dest_rect.top_left();
+    m_clip = dest_rect.intersected(painter.clip_rect());
+
+    if (m_clip.is_empty())
+        return;
+
+    auto& lines = path.split_lines();
+    if (lines.is_empty())
+        return;
+
+    auto edges = prepare_edges(lines, SamplesPerPixel, origin);
+
+    int min_scanline = m_size.height();
+    int max_scanline = 0;
+    for (auto& edge : edges) {
+        int start_scanline = edge.min_y / SamplesPerPixel;
+        int end_scanline = edge.max_y / SamplesPerPixel;
+
+        // Create a linked-list of edges starting on this scanline:
+        edge.next_edge = m_edge_table[start_scanline];
+        m_edge_table[start_scanline] = &edge;
+
+        min_scanline = min(min_scanline, start_scanline);
+        max_scanline = max(max_scanline, end_scanline);
+    }
+
+    Detail::Edge* active_edges = nullptr;
+
+    // FIXME: We could probably clip some of the egde plotting if we know it won't be shown.
+    // Though care would have to be taken to ensure the active edges are correct at the first drawn scaline.
+    if (winding_rule == Painter::WindingRule::EvenOdd) {
+        auto plot_edge = [&](Detail::Edge& edge, int start_subpixel_y, int end_subpixel_y) {
+            for (int y = start_subpixel_y; y < end_subpixel_y; y++) {
+                int xi = static_cast<int>(edge.x + SubpixelSample::nrooks_subpixel_offsets[y]);
+                SampleType sample = 1 << y;
+                m_scanline[xi] ^= sample;
+                edge.x += edge.dxdy;
+            }
+        };
+        for (int scanline = min_scanline; scanline <= max_scanline; scanline++) {
+            active_edges = plot_edges_for_scanline(scanline, plot_edge, active_edges);
+            accumulate_even_odd_scanline(painter, scanline, color_or_function);
+        }
+    } else {
+        VERIFY(winding_rule == Painter::WindingRule::Nonzero);
+        // Only allocate the winding buffer if needed.
+        // NOTE: non-zero fills are a fair bit less efficient. So if you can do an even-odd fill do that :^)
+        if (m_windings.is_empty())
+            m_windings.resize(m_size.width());
+
+        auto plot_edge = [&](Detail::Edge& edge, int start_subpixel_y, int end_subpixel_y) {
+            for (int y = start_subpixel_y; y < end_subpixel_y; y++) {
+                int xi = static_cast<int>(edge.x + SubpixelSample::nrooks_subpixel_offsets[y]);
+                SampleType sample = 1 << y;
+                m_scanline[xi] |= sample;
+                m_windings[xi].counts[y] += edge.winding;
+                edge.x += edge.dxdy;
+            }
+        };
+        for (int scanline = min_scanline; scanline <= max_scanline; scanline++) {
+            active_edges = plot_edges_for_scanline(scanline, plot_edge, active_edges);
+            accumulate_non_zero_scanline(painter, scanline, color_or_function);
+        }
+    }
+}
+
+template<unsigned SamplesPerPixel>
+Color EdgeFlagPathRasterizer<SamplesPerPixel>::scanline_color(int scanline, int offset, u8 alpha, auto& color_or_function)
+{
+    using ColorOrFunction = decltype(color_or_function);
+    constexpr bool has_constant_color = IsSame<RemoveCVReference<ColorOrFunction>, Color>;
+    auto color = [&] {
+        if constexpr (has_constant_color) {
+            return color_or_function;
+        } else {
+            return color_or_function({ offset, scanline });
+        }
+    }();
+    return color.with_alpha(color.alpha() * alpha / 255);
+}
+
+template<unsigned SamplesPerPixel>
+Detail::Edge* EdgeFlagPathRasterizer<SamplesPerPixel>::plot_edges_for_scanline(int scanline, auto plot_edge, Detail::Edge* active_edges)
+{
+    auto y_subpixel = [](int y) {
+        return y & (SamplesPerPixel - 1);
+    };
+
+    auto* current_edge = active_edges;
+    Detail::Edge* prev_edge = nullptr;
+
+    // First iterate over the edge in the active edge table, these are edges added on earlier scanlines,
+    // that have not yet reached their end scanline.
+    while (current_edge) {
+        int end_scanline = current_edge->max_y / SamplesPerPixel;
+        if (scanline == end_scanline) {
+            // This edge ends this scanline.
+            plot_edge(*current_edge, 0, y_subpixel(current_edge->max_y));
+            // Remove this edge from the AET
+            current_edge = current_edge->next_edge;
+            if (prev_edge)
+                prev_edge->next_edge = current_edge;
+            else
+                active_edges = current_edge;
+        } else {
+            // This egde sticks around for a few more scanlines.
+            plot_edge(*current_edge, 0, SamplesPerPixel);
+            prev_edge = current_edge;
+            current_edge = current_edge->next_edge;
+        }
+    }
+
+    // Next, iterate over new edges for this line. If active_edges was null this also becomes the new
+    // AET. Edges new will be appended here.
+    current_edge = m_edge_table[scanline];
+    while (current_edge) {
+        int end_scanline = current_edge->max_y / SamplesPerPixel;
+        if (scanline == end_scanline) {
+            // This edge will end this scanlines (no need to add to AET).
+            plot_edge(*current_edge, y_subpixel(current_edge->min_y), y_subpixel(current_edge->max_y));
+        } else {
+            // This edge will live on for a few more scanlines.
+            plot_edge(*current_edge, y_subpixel(current_edge->min_y), SamplesPerPixel);
+            // Add this edge to the AET
+            if (prev_edge)
+                prev_edge->next_edge = current_edge;
+            else
+                active_edges = current_edge;
+            prev_edge = current_edge;
+        }
+        current_edge = current_edge->next_edge;
+    }
+
+    m_edge_table[scanline] = nullptr;
+    return active_edges;
+}
+
+template<unsigned SamplesPerPixel>
+void EdgeFlagPathRasterizer<SamplesPerPixel>::write_pixel(Painter& painter, int scanline, int offset, SampleType sample, auto& color_or_function)
+{
+    auto dest = IntPoint { offset, scanline } + m_blit_origin;
+    if (!m_clip.contains_horizontally(dest.x()))
+        return;
+    // FIXME: We could detect runs of full coverage and use fast_u32_fills for those rather than many set_pixel() calls.
+    auto coverage = SubpixelSample::compute_coverage(sample);
+    if (coverage) {
+        auto paint_color = scanline_color(scanline, offset, coverage_to_alpha(coverage), color_or_function);
+        painter.set_physical_pixel(dest, paint_color, true);
+    }
+}
+
+template<unsigned SamplesPerPixel>
+void EdgeFlagPathRasterizer<SamplesPerPixel>::accumulate_even_odd_scanline(Painter& painter, int scanline, auto& color_or_function)
+{
+    auto dest_y = m_blit_origin.y() + scanline;
+    if (!m_clip.contains_vertically(dest_y)) {
+        // FIXME: This memset only really needs to be done on transition from clipped to not clipped,
+        // or not at all if we properly clipped egde plotting.
+        memset(m_scanline.data(), 0, sizeof(SampleType) * m_scanline.size());
+        return;
+    }
+
+    SampleType sample = 0;
+    for (int x = 0; x < m_size.width(); x += 1) {
+        sample ^= m_scanline[x];
+        write_pixel(painter, scanline, x, sample, color_or_function);
+        m_scanline[x] = 0;
+    }
+}
+
+template<unsigned SamplesPerPixel>
+void EdgeFlagPathRasterizer<SamplesPerPixel>::accumulate_non_zero_scanline(Painter& painter, int scanline, auto& color_or_function)
+{
+    // NOTE: Same FIXMEs apply from accumulate_even_odd_scanline()
+    auto dest_y = m_blit_origin.y() + scanline;
+    if (!m_clip.contains_vertically(dest_y)) {
+        memset(m_scanline.data(), 0, sizeof(SampleType) * m_scanline.size());
+        memset(m_windings.data(), 0, sizeof(WindingCounts) * m_windings.size());
+        return;
+    }
+
+    SampleType sample = 0;
+    WindingCounts sum_winding = {};
+    for (int x = 0; x < m_size.width(); x += 1) {
+        if (auto edges = m_scanline[x]) {
+            // We only need to process the windings when we hit some edges.
+            for (auto y_sub = 0u; y_sub < SamplesPerPixel; y_sub++) {
+                auto subpixel_bit = 1 << y_sub;
+                if (edges & subpixel_bit) {
+                    auto winding = m_windings[x].counts[y_sub];
+                    auto previous_winding_count = sum_winding.counts[y_sub];
+                    sum_winding.counts[y_sub] += winding;
+                    // Toggle fill on change to/from zero
+                    if ((previous_winding_count == 0 && sum_winding.counts[y_sub] != 0)
+                        || (sum_winding.counts[y_sub] == 0 && previous_winding_count != 0)) {
+                        sample ^= subpixel_bit;
+                    }
+                }
+            }
+        }
+        write_pixel(painter, scanline, x, sample, color_or_function);
+        m_scanline[x] = 0;
+        m_windings[x] = {};
+    }
+}
+
+static IntSize path_bounds(Gfx::Path const& path)
+{
+    return enclosing_int_rect(path.bounding_box()).size();
+}
+
+// Note: The AntiAliasingPainter and Painter now perform the same antialiasing,
+// since it would be harder to turn it off for the standard painter.
+// The samples are reduced to 8 for Gfx::Painter though as a "speedy" option.
+
+void Painter::fill_path(Path const& path, Color color, WindingRule winding_rule)
+{
+    EdgeFlagPathRasterizer<8> rasterizer(path_bounds(path));
+    rasterizer.fill(*this, path, color, winding_rule);
+}
+
+void Painter::fill_path(Path const& path, PaintStyle const& paint_style, Painter::WindingRule winding_rule)
+{
+    EdgeFlagPathRasterizer<8> rasterizer(path_bounds(path));
+    rasterizer.fill(*this, path, paint_style, winding_rule);
+}
+
+void AntiAliasingPainter::fill_path(Path const& path, Color color, Painter::WindingRule winding_rule)
+{
+    EdgeFlagPathRasterizer<32> rasterizer(path_bounds(path));
+    rasterizer.fill(m_underlying_painter, path, color, winding_rule, m_transform.translation());
+}
+
+void AntiAliasingPainter::fill_path(Path const& path, PaintStyle const& paint_style, Painter::WindingRule winding_rule)
+{
+    EdgeFlagPathRasterizer<32> rasterizer(path_bounds(path));
+    rasterizer.fill(m_underlying_painter, path, paint_style, winding_rule, m_transform.translation());
+}
+
+template class EdgeFlagPathRasterizer<8>;
+template class EdgeFlagPathRasterizer<16>;
+template class EdgeFlagPathRasterizer<32>;
+
+}
diff --git a/Userland/Libraries/LibGfx/EdgeFlagPathRasterizer.h b/Userland/Libraries/LibGfx/EdgeFlagPathRasterizer.h
new file mode 100644
index 0000000000..6c80e974f2
--- /dev/null
+++ b/Userland/Libraries/LibGfx/EdgeFlagPathRasterizer.h
@@ -0,0 +1,188 @@
+/*
+ * Copyright (c) 2023, MacDue <macdue@dueutil.tech>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Array.h>
+#include <AK/GenericShorthands.h>
+#include <AK/Vector.h>
+#include <LibGfx/Bitmap.h>
+#include <LibGfx/PaintStyle.h>
+#include <LibGfx/Painter.h>
+#include <LibGfx/Path.h>
+
+namespace Gfx {
+
+namespace Detail {
+
+static auto constexpr coverage_lut = [] {
+    Array<u8, 256> coverage_lut {};
+    for (u32 sample = 0; sample <= 255; sample++)
+        coverage_lut[sample] = popcount(sample);
+    return coverage_lut;
+}();
+
+template<unsigned SamplesPerPixel>
+struct Sample {
+    static_assert(!first_is_one_of(SamplesPerPixel, 8u, 16u, 32u), "EdgeFlagPathRasterizer: Invalid samples per pixel!");
+};
+
+// See paper for diagrams for how these offsets work, but they allow for nicely spread out samples in each pixel.
+template<>
+struct Sample<8> {
+    using Type = u8;
+    static constexpr Array nrooks_subpixel_offsets {
+        (5.0f / 8.0f),
+        (0.0f / 8.0f),
+        (3.0f / 8.0f),
+        (6.0f / 8.0f),
+        (1.0f / 8.0f),
+        (4.0f / 8.0f),
+        (7.0f / 8.0f),
+        (2.0f / 8.0f),
+    };
+
+    static u8 compute_coverage(Type sample)
+    {
+        return coverage_lut[sample];
+    }
+};
+
+template<>
+struct Sample<16> {
+    using Type = u16;
+    static constexpr Array nrooks_subpixel_offsets {
+        (1.0f / 16.0f),
+        (8.0f / 16.0f),
+        (4.0f / 16.0f),
+        (15.0f / 16.0f),
+        (11.0f / 16.0f),
+        (2.0f / 16.0f),
+        (6.0f / 16.0f),
+        (14.0f / 16.0f),
+        (10.0f / 16.0f),
+        (3.0f / 16.0f),
+        (7.0f / 16.0f),
+        (12.0f / 16.0f),
+        (0.0f / 16.0f),
+        (9.0f / 16.0f),
+        (5.0f / 16.0f),
+        (13.0f / 16.0f),
+    };
+
+    static u8 compute_coverage(Type sample)
+    {
+        return (
+            coverage_lut[(sample >> 0) & 0xff]
+            + coverage_lut[(sample >> 8) & 0xff]);
+    }
+};
+
+template<>
+struct Sample<32> {
+    using Type = u32;
+    static constexpr Array nrooks_subpixel_offsets {
+        (28.0f / 32.0f),
+        (13.0f / 32.0f),
+        (6.0f / 32.0f),
+        (23.0f / 32.0f),
+        (0.0f / 32.0f),
+        (17.0f / 32.0f),
+        (10.0f / 32.0f),
+        (27.0f / 32.0f),
+        (4.0f / 32.0f),
+        (21.0f / 32.0f),
+        (14.0f / 32.0f),
+        (31.0f / 32.0f),
+        (8.0f / 32.0f),
+        (25.0f / 32.0f),
+        (18.0f / 32.0f),
+        (3.0f / 32.0f),
+        (12.0f / 32.0f),
+        (29.0f / 32.0f),
+        (22.0f / 32.0f),
+        (7.0f / 32.0f),
+        (16.0f / 32.0f),
+        (1.0f / 32.0f),
+        (26.0f / 32.0f),
+        (11.0f / 32.0f),
+        (20.0f / 32.0f),
+        (5.0f / 32.0f),
+        (30.0f / 32.0f),
+        (15.0f / 32.0f),
+        (24.0f / 32.0f),
+        (9.0f / 32.0f),
+        (2.0f / 32.0f),
+        (19.0f / 32.0f),
+    };
+
+    static u8 compute_coverage(Type sample)
+    {
+        return (
+            coverage_lut[(sample >> 0) & 0xff]
+            + coverage_lut[(sample >> 8) & 0xff]
+            + coverage_lut[(sample >> 16) & 0xff]
+            + coverage_lut[(sample >> 24) & 0xff]);
+    }
+};
+
+struct Edge {
+    float x;
+    int min_y;
+    int max_y;
+    float dxdy;
+    i8 winding;
+    Edge* next_edge;
+};
+
+}
+
+template<unsigned SamplesPerPixel = 32>
+class EdgeFlagPathRasterizer {
+public:
+    EdgeFlagPathRasterizer(IntSize);
+
+    void fill(Painter&, Path const&, Color, Painter::WindingRule, FloatPoint offset = {});
+    void fill(Painter&, Path const&, PaintStyle const&, Painter::WindingRule, FloatPoint offset = {});
+
+private:
+    using SubpixelSample = Detail::Sample<SamplesPerPixel>;
+    using SampleType = typename SubpixelSample::Type;
+
+    static u8 coverage_to_alpha(u8 coverage)
+    {
+        constexpr auto alpha_shift = AK::log2(256 / SamplesPerPixel);
+        if (!coverage)
+            return 0;
+        return (coverage << alpha_shift) - 1;
+    }
+
+    void fill_internal(Painter&, Path const&, auto color_or_function, Painter::WindingRule, FloatPoint offset);
+    Detail::Edge* plot_edges_for_scanline(int scanline, auto plot_edge, Detail::Edge* active_edges = nullptr);
+    void accumulate_even_odd_scanline(Painter&, int scanline, auto& color_or_function);
+    void accumulate_non_zero_scanline(Painter&, int scanline, auto& color_or_function);
+    Color scanline_color(int scanline, int offset, u8 alpha, auto& color_or_function);
+    void write_pixel(Painter&, int scanline, int offset, SampleType sample, auto& color_or_function);
+
+    struct WindingCounts {
+        // NOTE: This only allows up to 256 winding levels. Increase this if required (i.e. to an i16).
+        i8 counts[SamplesPerPixel];
+    };
+
+    IntSize m_size;
+    IntPoint m_blit_origin;
+    IntRect m_clip;
+
+    Vector<SampleType> m_scanline;
+    Vector<WindingCounts> m_windings;
+    Vector<Detail::Edge*> m_edge_table;
+};
+
+extern template class EdgeFlagPathRasterizer<8>;
+extern template class EdgeFlagPathRasterizer<16>;
+extern template class EdgeFlagPathRasterizer<32>;
+
+}
diff --git a/Userland/Libraries/LibGfx/FillPathImplementation.cpp b/Userland/Libraries/LibGfx/FillPathImplementation.cpp
deleted file mode 100644
index cc89763835..0000000000
--- a/Userland/Libraries/LibGfx/FillPathImplementation.cpp
+++ /dev/null
@@ -1,299 +0,0 @@
-/*
- * Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
- * Copyright (c) 2023, MacDue <macdue@dueutil.tech>
- *
- * SPDX-License-Identifier: BSD-2-Clause
- */
-
-#include <AK/Debug.h>
-#include <AK/QuickSort.h>
-#include <LibGfx/Color.h>
-#include <LibGfx/Painter.h>
-#include <LibGfx/Path.h>
-
-#if defined(AK_COMPILER_GCC)
-#    pragma GCC optimize("O3")
-#endif
-
-namespace Gfx {
-
-template<typename T, typename TColorOrFunction>
-ALWAYS_INLINE void Painter::draw_scanline_for_fill_path(int y, T x_start, T x_end, TColorOrFunction color)
-{
-    // Fill path should scale the scanlines before calling this.
-    VERIFY(scale() == 1);
-
-    constexpr bool is_floating_point = IsSameIgnoringCV<T, float>;
-    constexpr bool has_constant_color = IsSameIgnoringCV<TColorOrFunction, Color>;
-
-    int x1 = 0;
-    int x2 = 0;
-    u8 left_subpixel_alpha = 0;
-    u8 right_subpixel_alpha = 0;
-    if constexpr (is_floating_point) {
-        x1 = ceilf(x_start);
-        x2 = floorf(x_end);
-        left_subpixel_alpha = (x1 - x_start) * 255;
-        right_subpixel_alpha = (x_end - x2) * 255;
-        x1 -= left_subpixel_alpha > 0;
-        x2 += right_subpixel_alpha > 0;
-    } else {
-        x1 = x_start;
-        x2 = x_end;
-    }
-
-    IntRect scanline(x1, y, x2 - x1, 1);
-    scanline = scanline.translated(translation());
-    auto clipped = scanline.intersected(clip_rect());
-    if (clipped.is_empty())
-        return;
-
-    auto get_color = [&](int offset) {
-        if constexpr (has_constant_color) {
-            return color;
-        } else {
-            return color(offset);
-        }
-    };
-
-    if constexpr (is_floating_point) {
-        // Paint left and right subpixels (then remove them from the scanline).
-        auto get_color_with_alpha = [&](int offset, u8 alpha) {
-            auto color_at_offset = get_color(offset);
-            u8 color_alpha = (alpha * color_at_offset.alpha()) / 255;
-            return color_at_offset.with_alpha(color_alpha);
-        };
-        bool paint_left_subpixel = clipped.left() == scanline.left() && left_subpixel_alpha;
-        bool paint_right_subpixel = clipped.right() == scanline.right() && right_subpixel_alpha;
-        if (paint_left_subpixel)
-            set_physical_pixel(clipped.top_left(), get_color_with_alpha(0, left_subpixel_alpha), true);
-        if (paint_right_subpixel)
-            set_physical_pixel(clipped.top_right().moved_left(1), get_color_with_alpha(scanline.width(), right_subpixel_alpha), true);
-        clipped.shrink(0, paint_right_subpixel, 0, paint_left_subpixel);
-        if (clipped.is_empty())
-            return;
-    }
-
-    if constexpr (has_constant_color) {
-        if (color.alpha() == 255) {
-            // Speedy path: Constant color and no alpha blending.
-            fast_u32_fill(m_target->scanline(clipped.y()) + clipped.x(), color.value(), clipped.width());
-            return;
-        }
-    }
-
-    for (int x = clipped.x(); x < clipped.right(); x++)
-        set_physical_pixel({ x, clipped.y() }, get_color(x - scanline.x()), true);
-}
-
-[[maybe_unused]] inline void approximately_place_on_int_grid(FloatPoint ffrom, FloatPoint fto, IntPoint& from, IntPoint& to, Optional<IntPoint> previous_to)
-{
-    auto diffs = fto - ffrom;
-    // Truncate all first (round down).
-    from = ffrom.to_type<int>();
-    to = fto.to_type<int>();
-    // There are 16 possible configurations, by deciding to round each
-    // coord up or down (and there are four coords, from.x from.y to.x to.y)
-    // we will simply choose one which most closely matches the correct slope
-    // with the following heuristic:
-    // - if the x diff is positive or zero (that is, a right-to-left slant), round 'from.x' up and 'to.x' down.
-    // - if the x diff is negative         (that is, a left-to-right slant), round 'from.x' down and 'to.x' up.
-    // Note that we do not need to touch the 'y' attribute, as that is our scanline.
-    if (diffs.x() >= 0) {
-        from.set_x(from.x() + 1);
-    } else {
-        to.set_x(to.x() + 1);
-    }
-    if (previous_to.has_value() && from.x() != previous_to.value().x()) // The points have to line up, since we're using these lines to fill a shape.
-        from.set_x(previous_to.value().x());
-}
-
-template<Painter::FillPathMode fill_path_mode, typename ColorOrFunction>
-void Painter::fill_path_impl(Path const& path, ColorOrFunction color, Gfx::Painter::WindingRule winding_rule, Optional<FloatPoint> offset)
-{
-    using GridCoordinateType = Conditional<fill_path_mode == FillPathMode::PlaceOnIntGrid, int, float>;
-    using PointType = Point<GridCoordinateType>;
-
-    auto draw_scanline = [&](int y, GridCoordinateType x1, GridCoordinateType x2) {
-        const auto draw_offset = offset.value_or({ 0, 0 });
-        // Note: .to_floored() is used here to be consistent with enclosing_int_rect()
-        const auto draw_origin = (path.bounding_box().top_left() + draw_offset).to_floored<int>();
-        // FIMXE: Offset is added here to handle floating point translations in the AA painter,
-        // really this should be done there but this function is a bit too specialised.
-        y = floorf(y + draw_offset.y());
-        x1 += draw_offset.x();
-        x2 += draw_offset.x();
-        if (x1 > x2)
-            swap(x1, x2);
-        if constexpr (IsSameIgnoringCV<ColorOrFunction, Color>) {
-            draw_scanline_for_fill_path(y, x1, x2, color);
-        } else {
-            draw_scanline_for_fill_path(y, x1, x2, [&](int offset) {
-                return color(IntPoint(x1 + offset, y) - draw_origin);
-            });
-        }
-    };
-
-    auto const& segments = path.split_lines();
-
-    if (segments.size() == 0)
-        return;
-
-    Vector<Path::SplitLineSegment> active_list;
-    active_list.ensure_capacity(segments.size());
-
-    // first, grab the segments for the very first scanline
-    GridCoordinateType first_y = path.bounding_box().bottom();
-    GridCoordinateType last_y = path.bounding_box().top() - 1;
-    float scanline = first_y;
-
-    size_t last_active_segment { 0 };
-
-    for (auto& segment : segments) {
-        if (segment.maximum_y != scanline)
-            break;
-        active_list.append(segment);
-        ++last_active_segment;
-    }
-
-    auto is_inside_shape = [winding_rule](int winding_number) {
-        if (winding_rule == Gfx::Painter::WindingRule::Nonzero)
-            return winding_number != 0;
-
-        if (winding_rule == Gfx::Painter::WindingRule::EvenOdd)
-            return winding_number % 2 == 0;
-
-        VERIFY_NOT_REACHED();
-    };
-
-    auto increment_winding = [winding_rule](int& winding_number, PointType const& from, PointType const& to) {
-        if (winding_rule == Gfx::Painter::WindingRule::EvenOdd) {
-            ++winding_number;
-            return;
-        }
-
-        if (winding_rule == Gfx::Painter::WindingRule::Nonzero) {
-            if (from.dy_relative_to(to) < 0)
-                ++winding_number;
-            else
-                --winding_number;
-            return;
-        }
-
-        VERIFY_NOT_REACHED();
-    };
-
-    while (scanline >= last_y) {
-        Optional<PointType> previous_to;
-        if (active_list.size()) {
-            // sort the active list by 'x' from right to left
-            quick_sort(active_list, [](auto const& line0, auto const& line1) {
-                return line1.x < line0.x;
-            });
-            if constexpr (fill_path_mode == FillPathMode::PlaceOnIntGrid && FILL_PATH_DEBUG) {
-                if ((int)scanline % 10 == 0) {
-                    draw_text(Gfx::Rect<GridCoordinateType>(active_list.last().x - 20, scanline, 20, 10), DeprecatedString::number((int)scanline));
-                }
-            }
-
-            if (active_list.size() > 1) {
-                auto winding_number { winding_rule == Gfx::Painter::WindingRule::Nonzero ? 1 : 0 };
-                for (size_t i = 1; i < active_list.size(); ++i) {
-                    auto& previous = active_list[i - 1];
-                    auto& current = active_list[i];
-
-                    PointType from, to;
-                    PointType truncated_from { previous.x, scanline };
-                    PointType truncated_to { current.x, scanline };
-                    if constexpr (fill_path_mode == FillPathMode::PlaceOnIntGrid) {
-                        approximately_place_on_int_grid({ previous.x, scanline }, { current.x, scanline }, from, to, previous_to);
-                    } else {
-                        from = truncated_from;
-                        to = truncated_to;
-                    }
-
-                    if (is_inside_shape(winding_number)) {
-                        // The points between this segment and the previous are
-                        // inside the shape
-
-                        dbgln_if(FILL_PATH_DEBUG, "y={}: {} at {}: {} -- {}", scanline, winding_number, i, from, to);
-                        draw_scanline(floorf(scanline), from.x(), to.x());
-                    }
-
-                    auto is_passing_through_maxima = scanline == previous.maximum_y
-                        || scanline == previous.minimum_y
-                        || scanline == current.maximum_y
-                        || scanline == current.minimum_y;
-
-                    auto is_passing_through_vertex = false;
-
-                    if (is_passing_through_maxima) {
-                        is_passing_through_vertex = previous.x == current.x;
-                    }
-
-                    if (!is_passing_through_vertex || previous.inverse_slope * current.inverse_slope < 0)
-                        increment_winding(winding_number, truncated_from, truncated_to);
-
-                    // update the x coord
-                    active_list[i - 1].x -= active_list[i - 1].inverse_slope;
-                }
-                active_list.last().x -= active_list.last().inverse_slope;
-            } else {
-                auto point = PointType(active_list[0].x, scanline);
-                draw_scanline(floorf(scanline), point.x(), point.x());
-
-                // update the x coord
-                active_list.first().x -= active_list.first().inverse_slope;
-            }
-        }
-
-        --scanline;
-        // remove any edge that goes out of bound from the active list
-        for (size_t i = 0, count = active_list.size(); i < count; ++i) {
-            if (scanline <= active_list[i].minimum_y) {
-                active_list.remove(i);
-                --count;
-                --i;
-            }
-        }
-        for (size_t j = last_active_segment; j < segments.size(); ++j, ++last_active_segment) {
-            auto& segment = segments[j];
-            if (segment.maximum_y < scanline)
-                break;
-            if (segment.minimum_y >= scanline)
-                continue;
-
-            active_list.append(segment);
-        }
-    }
-}
-
-void Painter::fill_path(Path const& path, Color color, WindingRule winding_rule)
-{
-    VERIFY(scale() == 1); // FIXME: Add scaling support.
-    fill_path_impl<FillPathMode::PlaceOnIntGrid>(path, color, winding_rule);
-}
-
-void Painter::fill_path(Path const& path, PaintStyle const& paint_style, Painter::WindingRule rule)
-{
-    VERIFY(scale() == 1); // FIXME: Add scaling support.
-    paint_style.paint(enclosing_int_rect(path.bounding_box()), [&](PaintStyle::SamplerFunction sampler) {
-        fill_path_impl<FillPathMode::PlaceOnIntGrid>(path, move(sampler), rule);
-    });
-}
-
-void Painter::antialiased_fill_path(Path const& path, Color color, WindingRule rule, FloatPoint translation)
-{
-    VERIFY(scale() == 1); // FIXME: Add scaling support.
-    fill_path_impl<FillPathMode::AllowFloatingPoints>(path, color, rule, translation);
-}
-
-void Painter::antialiased_fill_path(Path const& path, PaintStyle const& paint_style, WindingRule rule, FloatPoint translation)
-{
-    VERIFY(scale() == 1); // FIXME: Add scaling support.
-    paint_style.paint(enclosing_int_rect(path.bounding_box()), [&](PaintStyle::SamplerFunction sampler) {
-        fill_path_impl<FillPathMode::AllowFloatingPoints>(path, move(sampler), rule, translation);
-    });
-}
-
-}
diff --git a/Userland/Libraries/LibGfx/Painter.h b/Userland/Libraries/LibGfx/Painter.h
index 9ee3b68c16..cd668af928 100644
--- a/Userland/Libraries/LibGfx/Painter.h
+++ b/Userland/Libraries/LibGfx/Painter.h
@@ -187,6 +187,8 @@ public:
 protected:
     friend GradientLine;
     friend AntiAliasingPainter;
+    template<unsigned SamplesPerPixel>
+    friend class EdgeFlagPathRasterizer;
 
     IntRect to_physical(IntRect const& r) const { return r.translated(translation()) * scale(); }
     IntPoint to_physical(IntPoint p) const { return p.translated(translation()) * scale(); }
@@ -219,17 +221,6 @@ private:
     bool text_contains_bidirectional_text(Utf8View const&, TextDirection);
     template<typename DrawGlyphFunction>
     void do_draw_text(FloatRect const&, Utf8View const& text, Font const&, TextAlignment, TextElision, TextWrapping, DrawGlyphFunction);
-
-    void antialiased_fill_path(Path const&, Color, WindingRule rule, FloatPoint translation);
-    void antialiased_fill_path(Path const&, PaintStyle const& paint_style, WindingRule rule, FloatPoint translation);
-    enum class FillPathMode {
-        PlaceOnIntGrid,
-        AllowFloatingPoints,
-    };
-    template<typename T, typename TColorOrFunction>
-    void draw_scanline_for_fill_path(int y, T x_start, T x_end, TColorOrFunction color);
-    template<FillPathMode fill_path_mode, typename ColorOrFunction>
-    void fill_path_impl(Path const& path, ColorOrFunction color, Gfx::Painter::WindingRule winding_rule, Optional<FloatPoint> offset = {});
 };
 
 class PainterStateSaver {