LibWeb: Add "Label" to be the layout node for HTMLLabelElement

The HTML <label> element is special in that it may be associated with
some other <input> element. When the label element is clicked, the input
element should be activated.

To achieve this, a LableableNode base class is introduced to provide an
interface for "labelable" elements to handle mouse events on their
associated labels. This not only allows clicking the label to activate
the input, but dragging the mouse from the label to the input (and vice-
versa) while the mouse is clicked will also active the label.

As of this commit, this infrastructure is not hooked up to any elements.

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -165,6 +165,7 @@ set(SOURCES
     Layout/InitialContainingBlockBox.cpp
     Layout/InlineFormattingContext.cpp
     Layout/InlineNode.cpp
+    Layout/Label.cpp
     Layout/LayoutPosition.cpp
     Layout/LineBox.cpp
     Layout/LineBoxFragment.cpp

Userland/Libraries/LibWeb/Forward.h

@@ -174,6 +174,8 @@ class CheckBox;
 class FormattingContext;
 class InitialContainingBlockBox;
 class InlineFormattingContext;
+class Label;
+class LabelableNode;
 class LineBox;
 class LineBoxFragment;
 class Node;

Userland/Libraries/LibWeb/HTML/HTMLLabelElement.cpp

@@ -24,7 +24,9 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <LibWeb/DOM/Document.h>
 #include <LibWeb/HTML/HTMLLabelElement.h>
+#include <LibWeb/Layout/Label.h>
 
 namespace Web::HTML {
 
@@ -37,4 +39,15 @@ HTMLLabelElement::~HTMLLabelElement()
 {
 }
 
+RefPtr<Layout::Node> HTMLLabelElement::create_layout_node()
+{
+    auto style = document().style_resolver().resolve_style(*this);
+    if (style->display() == CSS::Display::None)
+        return nullptr;
+
+    auto layout_node = adopt(*new Layout::Label(document(), this, move(style)));
+    layout_node->set_inline(true);
+    return layout_node;
+}
+
 }

Userland/Libraries/LibWeb/HTML/HTMLLabelElement.h

@@ -36,6 +36,10 @@ public:
 
     HTMLLabelElement(DOM::Document&, QualifiedName);
     virtual ~HTMLLabelElement() override;
+
+    virtual RefPtr<Layout::Node> create_layout_node() override;
+
+    String for_() const { return attribute(HTML::AttributeNames::for_); }
 };
 
 }

Userland/Libraries/LibWeb/Layout/Label.cpp

@@ -0,0 +1,146 @@
+/*
+ * Copyright (c) 2021, Tim Flynn <trflynn89@pm.me>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <LibGUI/Event.h>
+#include <LibGfx/Painter.h>
+#include <LibGfx/StylePainter.h>
+#include <LibWeb/DOM/Document.h>
+#include <LibWeb/DOM/Element.h>
+#include <LibWeb/Layout/InitialContainingBlockBox.h>
+#include <LibWeb/Layout/Label.h>
+#include <LibWeb/Layout/LabelableNode.h>
+#include <LibWeb/Page/Frame.h>
+
+namespace Web::Layout {
+
+Label::Label(DOM::Document& document, HTML::HTMLLabelElement* element, NonnullRefPtr<CSS::StyleProperties> style)
+    : BlockBox(document, element, move(style))
+{
+}
+
+Label::~Label()
+{
+}
+
+void Label::handle_mousedown(Badge<EventHandler>, const Gfx::IntPoint&, unsigned button, unsigned)
+{
+    if (button != GUI::MouseButton::Left)
+        return;
+
+    if (auto* control = control_node(); control)
+        control->handle_associated_label_mousedown({});
+
+    m_tracking_mouse = true;
+}
+
+void Label::handle_mouseup(Badge<EventHandler>, const Gfx::IntPoint& position, unsigned button, unsigned)
+{
+    if (!m_tracking_mouse || button != GUI::MouseButton::Left)
+        return;
+
+    // NOTE: Changing the checked state of the DOM node may run arbitrary JS, which could disappear this node.
+    NonnullRefPtr protect = *this;
+
+    if (auto* control = control_node(); control) {
+        bool is_inside_control = enclosing_int_rect(control->absolute_rect()).contains(position);
+        bool is_inside_label = enclosing_int_rect(absolute_rect()).contains(position);
+
+        if (is_inside_control || is_inside_label)
+            control->handle_associated_label_mouseup({});
+    }
+
+    m_tracking_mouse = false;
+}
+
+void Label::handle_mousemove(Badge<EventHandler>, const Gfx::IntPoint& position, unsigned, unsigned)
+{
+    if (!m_tracking_mouse)
+        return;
+
+    if (auto* control = control_node(); control) {
+        bool is_inside_control = enclosing_int_rect(control->absolute_rect()).contains(position);
+        bool is_inside_label = enclosing_int_rect(absolute_rect()).contains(position);
+
+        control->handle_associated_label_mousemove({}, is_inside_control || is_inside_label);
+    }
+}
+
+bool Label::is_inside_associated_label(LabelableNode& control, const Gfx::IntPoint& position)
+{
+    if (auto* label = label_for_control_node(control); label)
+        return enclosing_int_rect(label->absolute_rect()).contains(position);
+    return false;
+}
+
+Label* Label::label_for_control_node(LabelableNode& control)
+{
+    Label* label = nullptr;
+
+    if (!control.document().layout_node())
+        return label;
+
+    String id = control.dom_node().attribute(HTML::AttributeNames::id);
+    if (id.is_empty())
+        return label;
+
+    control.document().layout_node()->for_each_in_subtree_of_type<Label>([&](auto& node) {
+        if (node.dom_node().for_() == id) {
+            label = &node;
+            return IterationDecision::Break;
+        }
+        return IterationDecision::Continue;
+    });
+
+    // FIXME: The spec also allows for associating a label with a labelable node by putting the
+    //        labelable node inside the label.
+    return label;
+}
+
+LabelableNode* Label::control_node()
+{
+    LabelableNode* control = nullptr;
+
+    if (!document().layout_node())
+        return control;
+
+    String for_ = dom_node().for_();
+    if (for_.is_empty())
+        return control;
+
+    document().layout_node()->for_each_in_subtree_of_type<LabelableNode>([&](auto& node) {
+        if (node.dom_node().attribute(HTML::AttributeNames::id) == for_) {
+            control = &node;
+            return IterationDecision::Break;
+        }
+        return IterationDecision::Continue;
+    });
+
+    // FIXME: The spec also allows for associating a label with a labelable node by putting the
+    //        labelable node inside the label.
+    return control;
+}
+
+}

Userland/Libraries/LibWeb/Layout/Label.h

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2021, Tim Flynn <trflynn89@pm.me>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <LibWeb/HTML/HTMLLabelElement.h>
+#include <LibWeb/Layout/BlockBox.h>
+
+namespace Web::Layout {
+
+class Label : public BlockBox {
+public:
+    Label(DOM::Document&, HTML::HTMLLabelElement*, NonnullRefPtr<CSS::StyleProperties>);
+    virtual ~Label() override;
+
+    static bool is_inside_associated_label(LabelableNode&, const Gfx::IntPoint&);
+
+    const HTML::HTMLLabelElement& dom_node() const { return static_cast<const HTML::HTMLLabelElement&>(*BlockBox::dom_node()); }
+    HTML::HTMLLabelElement& dom_node() { return static_cast<HTML::HTMLLabelElement&>(*BlockBox::dom_node()); }
+
+private:
+    virtual bool wants_mouse_events() const override { return true; }
+    virtual void handle_mousedown(Badge<EventHandler>, const Gfx::IntPoint&, unsigned button, unsigned modifiers) override;
+    virtual void handle_mouseup(Badge<EventHandler>, const Gfx::IntPoint&, unsigned button, unsigned modifiers) override;
+    virtual void handle_mousemove(Badge<EventHandler>, const Gfx::IntPoint&, unsigned button, unsigned modifiers) override;
+
+    static Label* label_for_control_node(LabelableNode&);
+    LabelableNode* control_node();
+
+    bool m_tracking_mouse { false };
+};
+
+}

Userland/Libraries/LibWeb/Layout/LabelableNode.h

@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2021, Tim Flynn <trflynn89@pm.me>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <LibWeb/Forward.h>
+#include <LibWeb/Layout/ReplacedBox.h>
+
+namespace Web::Layout {
+
+class LabelableNode : public ReplacedBox {
+public:
+    virtual void handle_associated_label_mousedown(Badge<Label>) { }
+    virtual void handle_associated_label_mouseup(Badge<Label>) { }
+    virtual void handle_associated_label_mousemove(Badge<Label>, [[maybe_unused]] bool is_inside_node_or_label) { }
+
+protected:
+    LabelableNode(DOM::Document& document, DOM::Element& element, NonnullRefPtr<CSS::StyleProperties> style)
+        : ReplacedBox(document, element, move(style))
+    {
+    }
+
+    virtual ~LabelableNode() = default;
+};
+
+}