LibWeb: Treat SVG fill/stroke/stroke-width attributes as CSS properties

Rather than having separate systems for the attributes and their CSS
equivalents, we can treat the attributes as presentational hints and
convert them to CSS properties. This means they can be inherited, as
they should. :^)

As noted, the `fill` and `stroke` attributes do not fully match the
`fill` and `stroke` properties. The CSS spec is still an early draft and
not entirely helpful, so we can just pretend they are the same for now.

Userland/Libraries/LibWeb/SVG/SVGGraphicsElement.cpp

@@ -1,10 +1,11 @@
 /*
  * Copyright (c) 2020, Matthew Olsson <mattco@serenityos.org>
- * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ * Copyright (c) 2021-2022, Sam Atkins <atkinssj@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <LibWeb/CSS/Parser/Parser.h>
 #include <LibWeb/SVG/SVGGraphicsElement.h>
 
 namespace Web::SVG {
@@ -14,25 +15,27 @@ SVGGraphicsElement::SVGGraphicsElement(DOM::Document& document, QualifiedName qu
 {
 }
 
-void SVGGraphicsElement::parse_attribute(FlyString const& name, String const& value)
+void SVGGraphicsElement::apply_presentational_hints(CSS::StyleProperties& style) const
 {
-    SVGElement::parse_attribute(name, value);
-
-    if (name == "fill") {
-        m_fill_color = Gfx::Color::from_string(value).value_or(Color::Transparent);
-    } else if (name == "stroke") {
-        m_stroke_color = Gfx::Color::from_string(value).value_or(Color::Transparent);
-    } else if (name == "stroke-width") {
-        auto result = value.to_int();
-        if (result.has_value())
-            m_stroke_width = result.value();
-    }
+    CSS::ParsingContext parsing_context { document() };
+    for_each_attribute([&](auto& name, auto& value) {
+        if (name.equals_ignoring_case("fill")) {
+            // FIXME: The `fill` attribute and CSS `fill` property are not the same! But our support is limited enough that they are equivalent for now.
+            if (auto fill_value = parse_css_value(parsing_context, value, CSS::PropertyID::Fill))
+                style.set_property(CSS::PropertyID::Fill, fill_value.release_nonnull());
+        } else if (name.equals_ignoring_case("stroke")) {
+            // FIXME: The `stroke` attribute and CSS `stroke` property are not the same! But our support is limited enough that they are equivalent for now.
+            if (auto stroke_value = parse_css_value(parsing_context, value, CSS::PropertyID::Stroke))
+                style.set_property(CSS::PropertyID::Stroke, stroke_value.release_nonnull());
+        } else if (name.equals_ignoring_case("stroke-width")) {
+            if (auto stroke_width_value = parse_css_value(parsing_context, value, CSS::PropertyID::StrokeWidth))
+                style.set_property(CSS::PropertyID::StrokeWidth, stroke_width_value.release_nonnull());
+        }
+    });
 }
 
 Optional<Gfx::Color> SVGGraphicsElement::fill_color() const
 {
-    if (m_fill_color.has_value())
-        return m_fill_color;
     if (!layout_node())
         return {};
     // FIXME: In the working-draft spec, `fill` is intended to be a shorthand, with `fill-color`
@@ -42,8 +45,6 @@ Optional<Gfx::Color> SVGGraphicsElement::fill_color() const
 
 Optional<Gfx::Color> SVGGraphicsElement::stroke_color() const
 {
-    if (m_stroke_color.has_value())
-        return m_stroke_color;
     if (!layout_node())
         return {};
     // FIXME: In the working-draft spec, `stroke` is intended to be a shorthand, with `stroke-color`
@@ -53,8 +54,6 @@ Optional<Gfx::Color> SVGGraphicsElement::stroke_color() const
 
 Optional<float> SVGGraphicsElement::stroke_width() const
 {
-    if (m_stroke_width.has_value())
-        return m_stroke_width;
     if (!layout_node())
         return {};
     // FIXME: Converting to pixels isn't really correct - values should be in "user units"

Userland/Libraries/LibWeb/SVG/SVGGraphicsElement.h

@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2020, Matthew Olsson <mattco@serenityos.org>
- * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ * Copyright (c) 2021-2022, Sam Atkins <atkinssj@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -20,16 +20,11 @@ public:
 
     SVGGraphicsElement(DOM::Document&, QualifiedName);
 
-    virtual void parse_attribute(FlyString const& name, String const& value) override;
+    virtual void apply_presentational_hints(CSS::StyleProperties&) const override;
 
     Optional<Gfx::Color> fill_color() const;
     Optional<Gfx::Color> stroke_color() const;
     Optional<float> stroke_width() const;
-
-protected:
-    Optional<Gfx::Color> m_fill_color;
-    Optional<Gfx::Color> m_stroke_color;
-    Optional<float> m_stroke_width;
 };
 
 }