Better piece flipping.

src/app/puzzle/layout/vppiece.cpp

@@ -243,3 +243,19 @@ void VPPiece::SetPatternLabelData(const VTextManager &data)
 {
     VLayoutPiece::SetPatternLabelData(data);
 }
+
+//---------------------------------------------------------------------------------------------------------------------
+void VPPiece::Flip()
+{
+    QTransform pieceMatrix = GetMatrix();
+    QPointF center = pieceMatrix.map(DetailBoundingRect().center());
+
+    QTransform m;
+    m.translate(center.x(), 0);
+    m.scale(-1, 1);
+    m.translate(-center.x(), 0);
+
+    pieceMatrix *= m;
+    SetMatrix(pieceMatrix);
+    SetMirror(!IsMirror());
+}

src/app/puzzle/layout/vppiece.h

@@ -101,6 +101,11 @@ public:
     auto GetPatternLabelData() const ->VTextManager;
     void SetPatternLabelData(const VTextManager &data);
 
+    /**
+     * @brief Flip horizontally mirror around center of bounding rect
+     */
+    void Flip();
+
 private:
     Q_DISABLE_COPY(VPPiece)
 

src/app/puzzle/vpmainwindow.cpp

@@ -570,11 +570,14 @@ void VPMainWindow::InitPropertyTabCurrentPiece()
             VPPiecePtr selectedPiece = selectedPieces.first();
             if (not selectedPiece.isNull())
             {
-                selectedPiece->SetMirror(checked);
+                if (selectedPiece->IsMirror() != checked)
+                {
+                    selectedPiece->Flip();
                     LayoutWasSaved(false);
                     emit m_layout->PieceTransformationChanged(selectedPiece);
                 }
             }
+        }
     });
 
     // Translate