LibWeb: Implement CSS `round()`

Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp

@@ -3963,6 +3963,74 @@ ErrorOr<OwnPtr<CalculationNode>> Parser::parse_exp_function(Function const& func
     return TRY(ExpCalculationNode::create(node_a.release_nonnull()));
 }
 
+ErrorOr<OwnPtr<CalculationNode>> Parser::parse_round_function(Function const& function)
+{
+    TokenStream stream { function.values() };
+    auto parameters = parse_a_comma_separated_list_of_component_values(stream);
+
+    if (parameters.size() != 2 && parameters.size() != 3) {
+        dbgln_if(CSS_PARSER_DEBUG, "round() must have exactly two or three parameters"sv);
+        return nullptr;
+    }
+
+    OwnPtr<CalculationNode> node_a = nullptr;
+    OwnPtr<CalculationNode> node_b = nullptr;
+    auto mode = CalculationNode::RoundingMode::Nearest;
+    if (parameters.size() == 3) {
+        auto rounding_mode_component = parameters[0][0];
+        if (!rounding_mode_component.is(Token::Type::Ident)) {
+            dbgln_if(CSS_PARSER_DEBUG, "round() mode must be a string"sv);
+            return nullptr;
+        }
+
+        auto mode_string = rounding_mode_component.token().ident();
+        if (mode_string.equals_ignoring_ascii_case("nearest"sv)) {
+            mode = CalculationNode::RoundingMode::Nearest;
+        } else if (mode_string.equals_ignoring_ascii_case("up"sv)) {
+            mode = CalculationNode::RoundingMode::Up;
+        } else if (mode_string.equals_ignoring_ascii_case("down"sv)) {
+            mode = CalculationNode::RoundingMode::Down;
+        } else if (mode_string.equals_ignoring_ascii_case("to-zero"sv)) {
+            mode = CalculationNode::RoundingMode::TowardZero;
+        } else {
+            dbgln_if(CSS_PARSER_DEBUG, "round() mode must be one of 'nearest', 'up', 'down', or 'to-zero'"sv);
+            return nullptr;
+        }
+
+        node_a = TRY(parse_a_calculation(parameters[1]));
+        node_b = TRY(parse_a_calculation(parameters[2]));
+    } else {
+        node_a = TRY(parse_a_calculation(parameters[0]));
+        node_b = TRY(parse_a_calculation(parameters[1]));
+    }
+
+    if (!node_a || !node_b) {
+        dbgln_if(CSS_PARSER_DEBUG, "round() parameters must be valid calculations"sv);
+        return nullptr;
+    }
+
+    auto node_a_maybe_parameter_type = node_a->resolved_type();
+    if (!node_a_maybe_parameter_type.has_value()) {
+        dbgln_if(CSS_PARSER_DEBUG, "Failed to resolve type for round() parameter 1"sv);
+        return nullptr;
+    }
+
+    auto node_b_maybe_parameter_type = node_b->resolved_type();
+    if (!node_b_maybe_parameter_type.has_value()) {
+        dbgln_if(CSS_PARSER_DEBUG, "Failed to resolve type for round() parameter 2"sv);
+        return nullptr;
+    }
+
+    auto node_a_resolved_type = node_a_maybe_parameter_type.value();
+    auto node_b_resolved_type = node_b_maybe_parameter_type.value();
+    if (node_a_resolved_type != node_b_resolved_type) {
+        dbgln_if(CSS_PARSER_DEBUG, "round() parameters must all be of the same type"sv);
+        return nullptr;
+    }
+
+    return TRY(RoundCalculationNode::create(mode, node_a.release_nonnull(), node_b.release_nonnull()));
+}
+
 ErrorOr<RefPtr<StyleValue>> Parser::parse_dynamic_value(ComponentValue const& component_value)
 {
     if (component_value.is_function()) {
@@ -4043,6 +4111,9 @@ ErrorOr<OwnPtr<CalculationNode>> Parser::parse_a_calc_function_node(Function con
     if (function.name().equals_ignoring_ascii_case("exp"sv))
         return TRY(parse_exp_function(function));
 
+    if (function.name().equals_ignoring_ascii_case("round"sv))
+        return TRY(parse_round_function(function));
+
     dbgln_if(CSS_PARSER_DEBUG, "We didn't implement `{}` function yet", function.name());
     return nullptr;
 }

Userland/Libraries/LibWeb/CSS/Parser/Parser.h

@@ -307,6 +307,7 @@ private:
     ErrorOr<OwnPtr<CalculationNode>> parse_hypot_function(Function const&);
     ErrorOr<OwnPtr<CalculationNode>> parse_log_function(Function const&);
     ErrorOr<OwnPtr<CalculationNode>> parse_exp_function(Function const&);
+    ErrorOr<OwnPtr<CalculationNode>> parse_round_function(Function const&);
     ErrorOr<RefPtr<StyleValue>> parse_dimension_value(ComponentValue const&);
     ErrorOr<RefPtr<StyleValue>> parse_integer_value(TokenStream<ComponentValue>&);
     ErrorOr<RefPtr<StyleValue>> parse_number_value(TokenStream<ComponentValue>&);

Userland/Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.cpp

@@ -1527,6 +1527,110 @@ ErrorOr<void> ExpCalculationNode::dump(StringBuilder& builder, int indent) const
     return {};
 }
 
+ErrorOr<NonnullOwnPtr<RoundCalculationNode>> RoundCalculationNode::create(RoundingMode mode, NonnullOwnPtr<CalculationNode> x, NonnullOwnPtr<CalculationNode> y)
+{
+    return adopt_nonnull_own_or_enomem(new (nothrow) RoundCalculationNode(mode, move(x), move(y)));
+}
+
+RoundCalculationNode::RoundCalculationNode(RoundingMode mode, NonnullOwnPtr<CalculationNode> x, NonnullOwnPtr<CalculationNode> y)
+    : CalculationNode(Type::Round)
+    , m_mode(mode)
+    , m_x(move(x))
+    , m_y(move(y))
+{
+}
+
+RoundCalculationNode::~RoundCalculationNode() = default;
+
+ErrorOr<String> RoundCalculationNode::to_string() const
+{
+    StringBuilder builder;
+    builder.append("round("sv);
+    switch (m_mode) {
+    case RoundingMode::Nearest:
+        builder.append("nearest"sv);
+        break;
+    case RoundingMode::Up:
+        builder.append("up"sv);
+        break;
+    case RoundingMode::Down:
+        builder.append("down"sv);
+        break;
+    case RoundingMode::TowardZero:
+        builder.append("toward-zero"sv);
+        break;
+    }
+    builder.append(", "sv);
+    builder.append(TRY(m_x->to_string()));
+    builder.append(", "sv);
+    builder.append(TRY(m_y->to_string()));
+    builder.append(")"sv);
+    return builder.to_string();
+}
+
+Optional<CalculatedStyleValue::ResolvedType> RoundCalculationNode::resolved_type() const
+{
+    // Note: We check during parsing that all values have the same type
+    return m_x->resolved_type();
+}
+
+bool RoundCalculationNode::contains_percentage() const
+{
+    return m_x->contains_percentage() || m_y->contains_percentage();
+}
+
+CalculatedStyleValue::CalculationResult RoundCalculationNode::resolve(Optional<Length::ResolutionContext const&> context, CalculatedStyleValue::PercentageBasis const& percentage_basis) const
+{
+    auto resolved_type = m_x->resolved_type().value();
+    auto node_a = m_x->resolve(context, percentage_basis);
+    auto node_b = m_y->resolve(context, percentage_basis);
+
+    auto node_a_value = resolve_value(node_a.value(), context);
+    auto node_b_value = resolve_value(node_b.value(), context);
+
+    auto upper_b = ceil(node_a_value / node_b_value) * node_b_value;
+    auto lower_b = floor(node_a_value / node_b_value) * node_b_value;
+
+    if (m_mode == RoundingMode::Nearest) {
+        auto upper_diff = fabs(upper_b - node_a_value);
+        auto lower_diff = fabs(node_a_value - lower_b);
+        auto rounded_value = upper_diff < lower_diff ? upper_b : lower_b;
+        return to_resolved_type(resolved_type, rounded_value);
+    }
+
+    if (m_mode == RoundingMode::Up) {
+        return to_resolved_type(resolved_type, upper_b);
+    }
+
+    if (m_mode == RoundingMode::Down) {
+        return to_resolved_type(resolved_type, lower_b);
+    }
+
+    if (m_mode == RoundingMode::TowardZero) {
+        auto upper_diff = fabs(upper_b);
+        auto lower_diff = fabs(lower_b);
+        auto rounded_value = upper_diff < lower_diff ? upper_b : lower_b;
+        return to_resolved_type(resolved_type, rounded_value);
+    }
+
+    VERIFY_NOT_REACHED();
+}
+
+ErrorOr<void> RoundCalculationNode::for_each_child_node(Function<ErrorOr<void>(NonnullOwnPtr<CalculationNode>&)> const& callback)
+{
+    TRY(m_x->for_each_child_node(callback));
+    TRY(m_y->for_each_child_node(callback));
+    TRY(callback(m_x));
+    TRY(callback(m_y));
+    return {};
+}
+
+ErrorOr<void> RoundCalculationNode::dump(StringBuilder& builder, int indent) const
+{
+    TRY(builder.try_appendff("{: >{}}ROUND: {}\n", "", indent, TRY(to_string())));
+    return {};
+}
+
 void CalculatedStyleValue::CalculationResult::add(CalculationResult const& other, Optional<Length::ResolutionContext const&> context, PercentageBasis const& percentage_basis)
 {
     add_or_subtract_internal(SumOperation::Add, other, context, percentage_basis);

Userland/Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.h

@@ -125,6 +125,14 @@ public:
         MinusInfinity,
     };
 
+    // https://drafts.csswg.org/css-values-4/#round-func
+    enum class RoundingMode {
+        Nearest,
+        Up,
+        Down,
+        TowardZero
+    };
+
     enum class Type {
         Numeric,
         // NOTE: Currently, any value with a `var()` or `attr()` function in it is always an
@@ -170,6 +178,12 @@ public:
         Log,
         Exp,
 
+        // Stepped value functions, a sub-type of operator node
+        // https://drafts.csswg.org/css-values-4/#round-func
+        Round,
+        Mod,
+        Rem,
+
         // This only exists during parsing.
         Unparsed,
     };
@@ -623,4 +637,24 @@ private:
     NonnullOwnPtr<CalculationNode> m_value;
 };
 
+class RoundCalculationNode final : public CalculationNode {
+public:
+    static ErrorOr<NonnullOwnPtr<RoundCalculationNode>> create(CalculationNode::RoundingMode, NonnullOwnPtr<CalculationNode>, NonnullOwnPtr<CalculationNode>);
+    ~RoundCalculationNode();
+
+    virtual ErrorOr<String> to_string() const override;
+    virtual Optional<CalculatedStyleValue::ResolvedType> resolved_type() const override;
+    virtual bool contains_percentage() const override;
+    virtual CalculatedStyleValue::CalculationResult resolve(Optional<Length::ResolutionContext const&>, CalculatedStyleValue::PercentageBasis const&) const override;
+    virtual ErrorOr<void> for_each_child_node(Function<ErrorOr<void>(NonnullOwnPtr<CalculationNode>&)> const&) override;
+
+    virtual ErrorOr<void> dump(StringBuilder&, int indent) const override;
+
+private:
+    RoundCalculationNode(RoundingMode, NonnullOwnPtr<CalculationNode>, NonnullOwnPtr<CalculationNode>);
+    CalculationNode::RoundingMode m_mode;
+    NonnullOwnPtr<CalculationNode> m_x;
+    NonnullOwnPtr<CalculationNode> m_y;
+};
+
 }