LibWeb: Pick up the CSS "visibility" property an honor it when painting

Userland/Libraries/LibWeb/CSS/ComputedValues.h

@@ -31,6 +31,7 @@ public:
     static Color color() { return Color::Black; }
     static Color background_color() { return Color::Transparent; }
     static CSS::ListStyleType list_style_type() { return CSS::ListStyleType::Disc; }
+    static CSS::Visibility visibility() { return CSS::Visibility::Visible; }
     static CSS::FlexDirection flex_direction() { return CSS::FlexDirection::Row; }
     static CSS::FlexWrap flex_wrap() { return CSS::FlexWrap::Nowrap; }
     static CSS::ImageRendering image_rendering() { return CSS::ImageRendering::Auto; }
@@ -127,6 +128,7 @@ public:
     float flex_shrink() const { return m_noninherited.flex_shrink; }
     CSS::AlignItems align_items() const { return m_noninherited.align_items; }
     float opacity() const { return m_noninherited.opacity; }
+    CSS::Visibility visibility() const { return m_inherited.visibility; }
     CSS::ImageRendering image_rendering() const { return m_inherited.image_rendering; }
     CSS::JustifyContent justify_content() const { return m_noninherited.justify_content; }
     Vector<BoxShadowData> const& box_shadow() const { return m_noninherited.box_shadow; }
@@ -191,6 +193,7 @@ protected:
         CSS::TextTransform text_transform { InitialValues::text_transform() };
         CSS::WhiteSpace white_space { InitialValues::white_space() };
         CSS::ListStyleType list_style_type { InitialValues::list_style_type() };
+        CSS::Visibility visibility { InitialValues::visibility() };
 
         Optional<Color> fill;
         Optional<Color> stroke;
@@ -303,6 +306,7 @@ public:
     void set_transformations(Vector<CSS::Transformation> value) { m_noninherited.transformations = move(value); }
     void set_box_sizing(CSS::BoxSizing value) { m_noninherited.box_sizing = value; }
     void set_vertical_align(Variant<CSS::VerticalAlign, CSS::LengthPercentage> value) { m_noninherited.vertical_align = value; }
+    void set_visibility(CSS::Visibility value) { m_inherited.visibility = value; }
 
     void set_fill(Color value) { m_inherited.fill = value; }
     void set_stroke(Color value) { m_inherited.stroke = value; }

Userland/Libraries/LibWeb/CSS/StyleProperties.cpp

@@ -698,6 +698,23 @@ Optional<CSS::Cursor> StyleProperties::cursor() const
     }
 }
 
+Optional<CSS::Visibility> StyleProperties::visibility() const
+{
+    auto value = property(CSS::PropertyID::Visibility);
+    if (!value.has_value() || !value.value()->is_identifier())
+        return {};
+    switch (value.value()->to_identifier()) {
+    case CSS::ValueID::Visible:
+        return CSS::Visibility::Visible;
+    case CSS::ValueID::Hidden:
+        return CSS::Visibility::Hidden;
+    case CSS::ValueID::Collapse:
+        return CSS::Visibility::Collapse;
+    default:
+        return {};
+    }
+}
+
 CSS::Display StyleProperties::display() const
 {
     auto value = property(CSS::PropertyID::Display);

Userland/Libraries/LibWeb/CSS/StyleProperties.h

@@ -66,6 +66,7 @@ public:
     float flex_shrink() const;
     Optional<CSS::AlignItems> align_items() const;
     float opacity() const;
+    Optional<CSS::Visibility> visibility() const;
     Optional<CSS::ImageRendering> image_rendering() const;
     Optional<CSS::JustifyContent> justify_content() const;
     Optional<CSS::Overflow> overflow_x() const;

Userland/Libraries/LibWeb/CSS/StyleValue.h

@@ -315,6 +315,12 @@ enum class VerticalAlign {
     Top,
 };
 
+enum class Visibility {
+    Visible,
+    Hidden,
+    Collapse,
+};
+
 enum class WhiteSpace {
     Normal,
     Pre,

Userland/Libraries/LibWeb/Layout/Node.cpp

@@ -465,7 +465,11 @@ void NodeWithStyle::apply_style(const CSS::StyleProperties& specified_style)
 
     computed_values.set_z_index(specified_style.z_index());
     computed_values.set_opacity(specified_style.opacity());
-    if (computed_values.opacity() == 0)
+
+    if (auto maybe_visibility = specified_style.visibility(); maybe_visibility.has_value())
+        computed_values.set_visibility(maybe_visibility.release_value());
+
+    if (computed_values.opacity() == 0 || computed_values.visibility() != CSS::Visibility::Visible)
         m_visible = false;
 
     if (auto maybe_length_percentage = specified_style.length_percentage(CSS::PropertyID::Width); maybe_length_percentage.has_value())