LibWeb: Implement interpolation of edge values

Author: https://github.com/tcl3
Commit: https://github.com/LadybirdBrowser/ladybird/commit/0beb22f19e7
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4315
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/shannonbooth

Libraries/LibWeb/CSS/Interpolation.cpp

@@ -577,6 +577,14 @@ NonnullRefPtr<CSSStyleValue const> interpolate_value(DOM::Element& element, Calc
         return delta >= 0.5f ? to : from;
     }
 
+    static auto interpolate_length_percentage = [](LengthPercentage const& from, LengthPercentage const& to, float delta) -> Optional<LengthPercentage> {
+        if (from.is_length() && to.is_length())
+            return Length::make_px(interpolate_raw(from.length().raw_value(), to.length().raw_value(), delta));
+        if (from.is_percentage() && to.is_percentage())
+            return Percentage(interpolate_raw(from.percentage().value(), to.percentage().value(), delta));
+        return {};
+    };
+
     switch (from.type()) {
     case CSSStyleValue::Type::Angle:
         return AngleStyleValue::create(Angle::make_degrees(interpolate_raw(from.as_angle().angle().to_degrees(), to.as_angle().angle().to_degrees(), delta)));
@@ -586,6 +594,17 @@ NonnullRefPtr<CSSStyleValue const> interpolate_value(DOM::Element& element, Calc
             layout_node = *node;
         return CSSColorValue::create_from_color(interpolate_color(from.to_color(layout_node), to.to_color(layout_node), delta), ColorSyntax::Modern);
     }
+    case CSSStyleValue::Type::Edge: {
+        auto resolved_from = from.as_edge().resolved_value(calculation_context);
+        auto resolved_to = to.as_edge().resolved_value(calculation_context);
+        auto const& edge = delta >= 0.5f ? resolved_to->edge() : resolved_from->edge();
+        auto const& from_offset = resolved_from->offset();
+        auto const& to_offset = resolved_to->offset();
+        if (auto interpolated_value = interpolate_length_percentage(from_offset, to_offset, delta); interpolated_value.has_value())
+            return EdgeStyleValue::create(edge, *interpolated_value);
+
+        return delta >= 0.5f ? to : from;
+    }
     case CSSStyleValue::Type::Integer: {
         // https://drafts.csswg.org/css-values/#combine-integers
         // Interpolation of <integer> is defined as Vresult = round((1 - p) × VA + p × VB);

Libraries/LibWeb/CSS/StyleValues/EdgeStyleValue.cpp

@@ -11,27 +11,9 @@ namespace Web::CSS {
 String EdgeStyleValue::to_string(SerializationMode mode) const
 {
     if (mode == CSSStyleValue::SerializationMode::ResolvedValue) {
-        if (edge() == PositionEdge::Right || edge() == PositionEdge::Bottom) {
-            if (offset().is_percentage()) {
-                auto flipped_percentage = 100 - offset().percentage().value();
-                return Percentage(flipped_percentage).to_string();
-            }
-
-            // FIXME: Figure out how to get the proper calculation context here
-            CalculationContext context = {};
-
-            Vector<NonnullRefPtr<CalculationNode const>> sum_parts;
-            sum_parts.append(NumericCalculationNode::create(Percentage(100), context));
-            if (offset().is_length()) {
-                sum_parts.append(NegateCalculationNode::create(NumericCalculationNode::create(offset().length(), context)));
-            } else {
-                // FIXME: Flip calculated offsets (convert CalculatedStyleValue to CalculationNode, then negate and append)
-                return to_string(CSSStyleValue::SerializationMode::Normal);
-            }
-            auto flipped_absolute = CalculatedStyleValue::create(SumCalculationNode::create(move(sum_parts)), CSSNumericType(CSSNumericType::BaseType::Length, 1), context);
-            return flipped_absolute->to_string(mode);
-        }
-        return offset().to_string();
+        // FIXME: Figure out how to get the proper calculation context here
+        CalculationContext context {};
+        return resolved_value(context)->offset().to_string();
     }
 
     StringBuilder builder;
@@ -48,4 +30,27 @@ String EdgeStyleValue::to_string(SerializationMode mode) const
     return builder.to_string_without_validation();
 }
 
+ValueComparingNonnullRefPtr<EdgeStyleValue const> EdgeStyleValue::resolved_value(CalculationContext context) const
+{
+    if (edge() == PositionEdge::Right || edge() == PositionEdge::Bottom) {
+        if (offset().is_percentage()) {
+            auto flipped_percentage = 100 - offset().percentage().value();
+            return create({}, Percentage(flipped_percentage));
+        }
+
+        Vector<NonnullRefPtr<CalculationNode const>> sum_parts;
+        sum_parts.append(NumericCalculationNode::create(Percentage(100), context));
+        if (offset().is_length()) {
+            sum_parts.append(NegateCalculationNode::create(NumericCalculationNode::create(offset().length(), context)));
+        } else {
+            // FIXME: Flip calculated offsets (convert CalculatedStyleValue to CalculationNode, then negate and append)
+            return *this;
+        }
+        auto flipped_absolute = CalculatedStyleValue::create(SumCalculationNode::create(move(sum_parts)), CSSNumericType(CSSNumericType::BaseType::Length, 1), context);
+        return create({}, flipped_absolute);
+    }
+
+    return *this;
+}
+
 }

Libraries/LibWeb/CSS/StyleValues/EdgeStyleValue.h

@@ -41,6 +41,8 @@ public:
 
     virtual String to_string(SerializationMode) const override;
 
+    ValueComparingNonnullRefPtr<EdgeStyleValue const> resolved_value(CalculationContext context) const;
+
     bool properties_equal(EdgeStyleValue const& other) const { return m_properties == other.m_properties; }
 
 private: