HackStudio: Start implementing basic widget selection in CursorTool

You can now select widgets by clicking on them with the CursorTool,
and toggle the selection state of a widget by Ctrl+clicking it.

DevTools/HackStudio/CursorTool.cpp

@@ -1,10 +1,21 @@
 #include "CursorTool.h"
+#include "FormEditorWidget.h"
+#include "FormWidget.h"
 #include <AK/LogStream.h>
 
 void CursorTool::on_mousedown(GMouseEvent& event)
 {
-    (void)event;
     dbg() << "CursorTool::on_mousedown";
+    auto& form_widget = m_editor.form_widget();
+    auto result = form_widget.hit_test(event.position(), GWidget::ShouldRespectGreediness::No);
+    if (result.widget && result.widget != &form_widget) {
+        if (event.modifiers() & Mod_Ctrl)
+            m_editor.selection().toggle(*result.widget);
+        else
+            m_editor.selection().set(*result.widget);
+        // FIXME: Do we need to update any part of the FormEditorWidget outside the FormWidget?
+        form_widget.update();
+    }
 }
 
 void CursorTool::on_mouseup(GMouseEvent& event)

DevTools/HackStudio/FormEditorWidget.h

@@ -18,12 +18,61 @@ public:
 
     void set_tool(NonnullOwnPtr<Tool>);
 
+    class WidgetSelection {
+    public:
+        bool is_empty() const
+        {
+            return m_widgets.is_empty();
+        }
+
+        bool contains(GWidget& widget) const
+        {
+            return m_widgets.contains(&widget);
+        }
+
+        void toggle(GWidget& widget)
+        {
+            if (contains(widget))
+                remove(widget);
+            else
+                add(widget);
+        }
+
+        void set(GWidget& widget)
+        {
+            clear();
+            add(widget);
+        }
+
+        void remove(GWidget& widget)
+        {
+            ASSERT(m_widgets.contains(&widget));
+            m_widgets.remove(&widget);
+        }
+
+        void add(GWidget& widget)
+        {
+            m_widgets.set(&widget);
+        }
+
+        void clear()
+        {
+            m_widgets.clear();
+        }
+
+        WidgetSelection() {}
+    private:
+        HashTable<GWidget*> m_widgets;
+    };
+
+    WidgetSelection& selection() { return m_selection; }
+
 private:
     virtual void paint_event(GPaintEvent&) override;
 
     explicit FormEditorWidget(GWidget* parent);
 
     RefPtr<FormWidget> m_form_widget;
-
     NonnullOwnPtr<Tool> m_tool;
+    WidgetSelection m_selection;
 };

DevTools/HackStudio/FormWidget.cpp

@@ -39,6 +39,21 @@ void FormWidget::paint_event(GPaintEvent& event)
     }
 }
 
+void FormWidget::second_paint_event(GPaintEvent& event)
+{
+    if (editor().selection().is_empty())
+        return;
+
+    GPainter painter(*this);
+    painter.add_clip_rect(event.rect());
+    for_each_child_widget([&](auto& child) {
+        if (editor().selection().contains(child)) {
+            painter.draw_rect(child.relative_rect(), Color::Blue);
+        }
+        return IterationDecision::Continue;
+    });
+}
+
 void FormWidget::mousedown_event(GMouseEvent& event)
 {
     editor().tool().on_mousedown(event);

DevTools/HackStudio/FormWidget.h

@@ -14,6 +14,7 @@ public:
 
 private:
     virtual void paint_event(GPaintEvent&) override;
+    virtual void second_paint_event(GPaintEvent&) override;
     virtual void mousedown_event(GMouseEvent&) override;
     virtual void mouseup_event(GMouseEvent&) override;
     virtual void mousemove_event(GMouseEvent&) override;