GWidget: Add move_by() and make set_relative_rect() invalidate parent.

Author: awesomekling

LibGUI/GWidget.cpp

@@ -43,6 +43,9 @@ void GWidget::set_relative_rect(const Rect& rect)
 {
     if (rect == m_relative_rect)
         return;
+
+    auto old_rect = m_relative_rect;
+
     bool size_changed = m_relative_rect.size() != rect.size();
     m_relative_rect = rect;
 
@@ -51,6 +54,8 @@ void GWidget::set_relative_rect(const Rect& rect)
         event(resize_event);
     }
 
+    if (auto* parent = parent_widget())
+        parent->update(old_rect);
     update();
 }
 

LibGUI/GWidget.h

@@ -112,6 +112,9 @@ class GWidget : public CObject {
     void resize(const Size& size) { set_relative_rect({ relative_rect().location(), size }); }
     void resize(int width, int height) { resize({ width, height }); }
 
+    void move_by(int x, int y) { move_by({ x, y }); }
+    void move_by(const Point& delta) { set_relative_rect({ relative_position().translated(delta), size() }); }
+
     Color background_color() const { return m_background_color; }
     Color foreground_color() const { return m_foreground_color; }