如何获得Windows窗体相对于显示器的正确位置?

我找了几个小时,试了很多东西。

[DllImport("user32.dll")]
public static extern IntPtr GetDC(IntPtr ptr);

[DllImport("user32.dll")]
public static extern bool ReleaseDC(IntPtr hWnd, IntPtr hDC);

private void LocationChanged(object sender, EventArgs e)
{
    var position = form.PointToScreen(Point.Empty);
    bounds = new Rectangle(position, new Size(50, 50));
    DrawRectangle(bounds);
}

void DrawRectangle(Rectangle rect)
{
    IntPtr desktopPtr = GetDC(IntPtr.Zero);
    Graphics g = Graphics.FromHdc(desktopPtr);

    SolidBrush b = new SolidBrush(Color.Green);
    g.FillRectangle(b, rect);

    g.Dispose();
    ReleaseDC(IntPtr.Zero, desktopPtr);
}

结果是:

绿色方块应该完全覆盖表单,左边有红色边框。

如果不是怎么办? ),我试着通过 form.Location 到 form.PointToScreen

我做错什么了?