Не удалять нарисованное в PictureBox при Refresh

Graphics ^g = Graphics::FromImage(pictureBox1->Image);
g->DrawLine(Pens::Red, 0, 0, 100, 100);
pictureBox1->Refresh();
g->Dispose();

private: System::Void pictureBox1_Paint(System::Object^  sender, System::Windows::Forms::PaintEventArgs^  e) 
         {   Brush^ brush=gcnew SolidBrush(colorDialog2->Color);
             Pen^ pen=gcnew Pen(colorDialog1->Color);
             if (comboBox1->SelectedIndex==0) 
             {
                 e->Graphics->DrawLine(pen, a, b, c, d);
                 e->Graphics->DrawLine(pen, c, d, t, f); 
                 e->Graphics->DrawLine(pen, t, f, a, b);
                 Point point1 = Point(a,b);
                 Point point2 = Point(c,d);
                 Point point3 = Point(t,f);
                 array<Point>^ points = {point1,point2,point3};
                 e->Graphics->FillPolygon(brush, points);
             }
             if (comboBox1->SelectedIndex==1)
             {  
                e->Graphics->DrawEllipse(pen, c, d, a, b);
                e->Graphics->FillEllipse(brush, c, d, a, b);
             }
             if (comboBox1->SelectedIndex==2)
             {  
                e->Graphics->DrawEllipse(pen, c, d, a, a);
                e->Graphics->FillEllipse(brush, c, d, a, a);
             }
         }

delete g;