winform 鼠标拖动移动图片位置

private void pbMain_MouseDown(object sender, MouseEventArgs e)
{
photo_rec = photo_show1.GetPictureBoxZoomSize(pictureBox1);
pt = Cursor.Position;
this.Cursor = Cursors.SizeAll;
}
private void pbMain_MouseUp(object sender, MouseEventArgs e)
{
this.Cursor = Cursors.Default;
int px = Cursor.Position.X - pt.X;
int py = Cursor.Position.Y - pt.Y;
}
private void pbMain_MouseMove(object sender, MouseEventArgs e)
{
if (e.Button == MouseButtons.Left)
{
int px = Cursor.Position.X - pt.X;
int py = Cursor.Position.Y - pt.Y;
pictureBox1.Location = new Point(pictureBox1.Location.X + px, pictureBox1.Location.Y + py);
}
pt = Cursor.Position;
}
}