LibWeb: Let Paintable perform the painting

This patch adds a bunch of Paintable subclasses, each corresponding to
the Layout::Node subclasses that had a paint() override. All painting
logic is moved from layout nodes into their corresponding paintables.

Paintables are now created by asking a Layout::Box to produce one:

    static NonnullOwnPtr<Paintable> Layout::Box::create_paintable()

Note that inline nodes still have their painting logic. Since they
are not boxes, and all paintables have a corresponding box, we'll need
to come up with some other solution for them.

1 files changed, 122 insertions, 0 deletions

diff --git a/Userland/Libraries/LibWeb/Painting/SVGGeometryPaintable.cpp b/Userland/Libraries/LibWeb/Painting/SVGGeometryPaintable.cpp
new file mode 100644
index 0000000000..f238b9a8a8
--- /dev/null
+++ b/Userland/Libraries/LibWeb/Painting/SVGGeometryPaintable.cpp
@@ -0,0 +1,122 @@
+/*
+ * Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibGfx/AntiAliasingPainter.h>
+#include <LibWeb/Layout/ImageBox.h>
+#include <LibWeb/Painting/SVGGeometryPaintable.h>
+#include <LibWeb/SVG/SVGSVGElement.h>
+
+namespace Web::Painting {
+
+NonnullOwnPtr<SVGGeometryPaintable> SVGGeometryPaintable::create(Layout::SVGGeometryBox const& layout_box)
+{
+    return adopt_own(*new SVGGeometryPaintable(layout_box));
+}
+
+SVGGeometryPaintable::SVGGeometryPaintable(Layout::SVGGeometryBox const& layout_box)
+    : SVGGraphicsPaintable(layout_box)
+{
+}
+
+Layout::SVGGeometryBox const& SVGGeometryPaintable::layout_box() const
+{
+    return static_cast<Layout::SVGGeometryBox const&>(m_layout_box);
+}
+
+void SVGGeometryPaintable::paint(PaintContext& context, PaintPhase phase) const
+{
+    if (!is_visible())
+        return;
+
+    SVGGraphicsPaintable::paint(context, phase);
+
+    if (phase != PaintPhase::Foreground)
+        return;
+
+    auto& geometry_element = layout_box().dom_node();
+
+    Gfx::AntiAliasingPainter painter { context.painter() };
+    auto& svg_context = context.svg_context();
+
+    auto offset = svg_context.svg_element_position();
+    painter.translate(offset);
+
+    auto const* svg_element = geometry_element.first_ancestor_of_type<SVG::SVGSVGElement>();
+    auto maybe_view_box = svg_element->view_box();
+
+    context.painter().add_clip_rect(enclosing_int_rect(absolute_rect()));
+
+    Gfx::Path path = const_cast<SVG::SVGGeometryElement&>(geometry_element).get_path();
+
+    if (maybe_view_box.has_value()) {
+        Gfx::Path new_path;
+        auto scaling = layout_box().viewbox_scaling();
+        auto origin = layout_box().viewbox_origin();
+
+        auto transform_point = [&scaling, &origin](Gfx::FloatPoint const& point) -> Gfx::FloatPoint {
+            auto new_point = point;
+            new_point.translate_by({ -origin.x(), -origin.y() });
+            new_point.scale_by(scaling);
+            return new_point;
+        };
+
+        for (auto& segment : path.segments()) {
+            switch (segment.type()) {
+            case Gfx::Segment::Type::Invalid:
+                break;
+            case Gfx::Segment::Type::MoveTo:
+                new_path.move_to(transform_point(segment.point()));
+                break;
+            case Gfx::Segment::Type::LineTo:
+                new_path.line_to(transform_point(segment.point()));
+                break;
+            case Gfx::Segment::Type::QuadraticBezierCurveTo: {
+                auto& quadratic_bezier_segment = static_cast<Gfx::QuadraticBezierCurveSegment const&>(segment);
+                new_path.quadratic_bezier_curve_to(transform_point(quadratic_bezier_segment.through()), transform_point(quadratic_bezier_segment.point()));
+                break;
+            }
+            case Gfx::Segment::Type::CubicBezierCurveTo: {
+                auto& cubic_bezier_segment = static_cast<Gfx::CubicBezierCurveSegment const&>(segment);
+                new_path.cubic_bezier_curve_to(transform_point(cubic_bezier_segment.through_0()), transform_point(cubic_bezier_segment.through_1()), transform_point(cubic_bezier_segment.point()));
+                break;
+            }
+            case Gfx::Segment::Type::EllipticalArcTo: {
+                auto& elliptical_arc_segment = static_cast<Gfx::EllipticalArcSegment const&>(segment);
+                new_path.elliptical_arc_to(transform_point(elliptical_arc_segment.point()), elliptical_arc_segment.radii().scaled(scaling, scaling), elliptical_arc_segment.x_axis_rotation(), false, false);
+                break;
+            }
+            }
+        }
+
+        path = new_path;
+    }
+
+    if (auto fill_color = geometry_element.fill_color().value_or(svg_context.fill_color()); fill_color.alpha() > 0) {
+        // We need to fill the path before applying the stroke, however the filled
+        // path must be closed, whereas the stroke path may not necessary be closed.
+        // Copy the path and close it for filling, but use the previous path for stroke
+        auto closed_path = path;
+        closed_path.close();
+
+        // Fills are computed as though all paths are closed (https://svgwg.org/svg2-draft/painting.html#FillProperties)
+        painter.fill_path(
+            closed_path,
+            fill_color,
+            Gfx::Painter::WindingRule::EvenOdd);
+    }
+
+    if (auto stroke_color = geometry_element.stroke_color().value_or(svg_context.stroke_color()); stroke_color.alpha() > 0) {
+        painter.stroke_path(
+            path,
+            stroke_color,
+            geometry_element.stroke_width().value_or(svg_context.stroke_width()));
+    }
+
+    painter.translate(-offset);
+    context.painter().clear_clip_rect();
+}
+
+}