HackStudio: Allow rubber-band selection of widgets

This patch implements basic rubber-banding. Perhaps this mechanism can
be generalized somehow, but it's not clear to me how that would work
at the moment.

DevTools/HackStudio/CursorTool.cpp

@@ -29,6 +29,8 @@ void CursorTool::on_mousedown(GMouseEvent& event)
             }
         } else {
             m_editor.selection().clear();
+            form_widget.set_rubber_banding({}, true);
+            form_widget.set_rubber_band_origin({}, event.position());
         }
         // FIXME: Do we need to update any part of the FormEditorWidget outside the FormWidget?
         form_widget.update();
@@ -49,15 +51,21 @@ void CursorTool::on_mouseup(GMouseEvent& event)
             }
         }
         m_dragging = false;
+        form_widget.set_rubber_banding({}, false);
     }
 }
 
 void CursorTool::on_mousemove(GMouseEvent& event)
 {
     dbg() << "CursorTool::on_mousemove";
+    auto& form_widget = m_editor.form_widget();
+
+    if (form_widget.is_rubber_banding({})) {
+        form_widget.set_rubber_band_position({}, event.position());
+        return;
+    }
 
     if (!m_dragging && event.buttons() & GMouseButton::Left && event.position() != m_drag_origin) {
-        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 (!m_editor.selection().contains(*result.widget)) {
@@ -82,6 +90,7 @@ void CursorTool::on_mousemove(GMouseEvent& event)
         m_editor.model().update();
         return;
     }
+
 }
 
 void CursorTool::on_keydown(GKeyEvent& event)

DevTools/HackStudio/FormWidget.cpp

@@ -41,17 +41,20 @@ 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());
+
+    if (!editor().selection().is_empty()) {
         for_each_child_widget([&](auto& child) {
             if (editor().selection().contains(child)) {
                 painter.draw_rect(child.relative_rect(), Color::Blue);
             }
             return IterationDecision::Continue;
         });
+    }
+
+    if (m_rubber_banding)
+        painter.draw_rect(rubber_band_rect(), Color::MidMagenta);
 }
 
 void FormWidget::mousedown_event(GMouseEvent& event)
@@ -73,3 +76,59 @@ void FormWidget::keydown_event(GKeyEvent& event)
 {
     editor().tool().on_keydown(event);
 }
+
+void FormWidget::set_rubber_banding(Badge<CursorTool>, bool value)
+{
+    if (m_rubber_banding == value)
+        return;
+    m_rubber_banding = value;
+    update();
+}
+
+void FormWidget::set_rubber_band_origin(Badge<CursorTool>, const Point& origin)
+{
+    if (m_rubber_band_origin == origin)
+        return;
+    m_rubber_band_origin = origin;
+    m_rubber_band_position = origin;
+    update();
+}
+
+void FormWidget::set_rubber_band_position(Badge<CursorTool>, const Point& position)
+{
+    if (m_rubber_band_position == position)
+        return;
+    m_rubber_band_position = position;
+
+    auto rubber_band_rect = this->rubber_band_rect();
+
+    editor().selection().clear();
+    for_each_child_widget([&](auto& child) {
+        if (child.relative_rect().intersects(rubber_band_rect))
+            editor().selection().add(child);
+        return IterationDecision::Continue;
+    });
+
+    update();
+}
+
+static Rect rect_from_two_points(const Point& a, const Point& b)
+{
+    if (a.x() <= b.x()) {
+        if (a.y() <= b.y())
+            return { a, { b.x() - a.x(), b.y() - a.y() } };
+        int height = a.y() - b.y();
+        return { a.x(), a.y() - height, b.x() - a.x(), height };
+    }
+    if (a.y() >= b.y())
+        return { b, { a.x() - b.x(), a.y() - b.y() } };
+    int height = b.y() - a.y();
+    return { b.x(), b.y() - height, a.x() - b.x(), height };
+}
+
+Rect FormWidget::rubber_band_rect() const
+{
+    if (!m_rubber_banding)
+        return {};
+    return rect_from_two_points(m_rubber_band_origin, m_rubber_band_position);
+}

DevTools/HackStudio/FormWidget.h

@@ -1,7 +1,9 @@
 #pragma once
 
+#include <AK/Badge.h>
 #include <LibGUI/GWidget.h>
 
+class CursorTool;
 class FormEditorWidget;
 
 class FormWidget final : public GWidget {
@@ -15,6 +17,11 @@ public:
     // FIXME: This should be an app-wide preference instead.
     int grid_size() const { return m_grid_size; }
 
+    bool is_rubber_banding(Badge<CursorTool>) const { return m_rubber_banding; }
+    void set_rubber_banding(Badge<CursorTool>, bool);
+    void set_rubber_band_position(Badge<CursorTool>, const Point&);
+    void set_rubber_band_origin(Badge<CursorTool>, const Point&);
+
 private:
     virtual bool accepts_focus() const override { return true; }
 
@@ -27,5 +34,11 @@ private:
 
     explicit FormWidget(FormEditorWidget& parent);
 
+    Rect rubber_band_rect() const;
+
     int m_grid_size { 5 };
+
+    bool m_rubber_banding { false };
+    Point m_rubber_band_origin;
+    Point m_rubber_band_position;
 };