Lots of fixes and added more dialogs

drawingcanvaswidget.cpp

@@ -27,11 +27,33 @@ void DrawingCanvasWidget::setScale(float scale)
 
 void DrawingCanvasWidget::paintEvent(QPaintEvent *ev)
 {
-    QWidget::paintEvent(ev);
-
     if (!m_pixmap)
+    {
+        QWidget::paintEvent(ev);
         return;
+    }
+
+    QBrush brush;
+    {
+        QPixmap pixmap{32, 32};
+        {
+            QPainter painter{&pixmap};
+            painter.setPen(Qt::NoPen);
+            painter.setBrush(Qt::gray);
+            painter.drawRect(0, 0, 16, 16);
+            painter.drawRect(16, 16, 16, 16);
+            painter.setBrush(Qt::white);
+            painter.drawRect(0, 16, 16, 16);
+            painter.drawRect(16, 0, 16, 16);
+        }
+        brush.setTexture(std::move(pixmap));
+    }
 
     QPainter painter{this};
-    painter.drawPixmap(QRect{QPoint{}, m_pixmap->size() * m_scale}, *m_pixmap);
+
+    painter.setPen(Qt::NoPen);
+    painter.setBrush(std::move(brush));
+    painter.drawRect(rect());
+
+    painter.drawPixmap(rect(), *m_pixmap);
 }