使用GDI32椭圆，如.net drawlipse

在c#中，我可以使用。net System.Graphics.DrawEllipse方法在从Windows Calculator (calc.exe)窗口获取的屏幕设备上下文上绘制椭圆。

我希望能够用GDI32椭圆方法做同样的事情。如何使椭圆绘制到屏幕上?

在下面的代码中，这行行得通:CalculatorGraphics。drawlipse (penRed, 50,50,50,50);但这句话没有:PlatformInvokeGDI32。椭圆(hDC, 100,100,100,100);有什么问题吗?

        //In size variable we shall keep the size of the window.
        SIZE size;
        //Win32 API functions are imported in classes
        //PlatformInvokeGDI32
        //PlatformInvokeUSER32.cs
        //Get handle of calc.exe window.
        IntPtr hwnd = PlatformInvokeUSER32.FindWindow("SciCalc", "Calculator");
        //Get window dimensions
        PlatformInvokeUSER32.RECT rect;
        PlatformInvokeUSER32.GetWindowRect(hwnd, out rect);
        size.cx = rect._Right - rect._Left;
        size.cy = rect._Bottom - rect._Top;
        //Get the device context of Calculator.
        IntPtr hDC = PlatformInvokeUSER32.GetDC(hwnd);
        //Draw on the Calculator surface.
        Graphics CalculatorGraphics = Graphics.FromHdc(hDC);
        Color colorRed = Color.FromName("Red");
        Pen penRed = new Pen(colorRed);
        CalculatorGraphics.DrawEllipse(penRed, 50, 50, 50, 50);
        CalculatorGraphics.Save();
        PlatformInvokeGDI32.COLORREF cl;
        cl.R = 255;
        cl.G = 0;
        cl.B = 0;
        PlatformInvokeGDI32.SetDCBrushColor(hDC, cl);
        PlatformInvokeGDI32.SetDCPenColor(hDC, cl);
        //PlatformInvokeGDI32.SetBkColor(hDC, cl);
        PlatformInvokeGDI32.Ellipse(hDC, 100, 100, 100, 100);
        PlatformInvokeGDI32.SaveDC(hDC);

        //Here we make a compatible device context in memory for screen device context.
        IntPtr hMemDC = PlatformInvokeGDI32.CreateCompatibleDC(hDC);

        //Create a compatible bitmap of window size and using screen device context.
        m_HBitmap = PlatformInvokeGDI32.CreateCompatibleBitmap(hDC, size.cx, size.cy);
        //As m_HBitmap is IntPtr we can not check it against null. For this purspose IntPtr.Zero is used.
        if (m_HBitmap != IntPtr.Zero)
        {
            //Here we select the compatible bitmap in memeory device context and keeps the refrence to Old bitmap.
            IntPtr hOld = (IntPtr)PlatformInvokeGDI32.SelectObject(hMemDC, m_HBitmap);
            //We copy the Bitmap to the memory device context.
            PlatformInvokeGDI32.BitBlt(hMemDC, 0, 0, size.cx, size.cy, hDC, 0, 0, PlatformInvokeGDI32.SRCCOPY);
            //We select the old bitmap back to the memory device context.
            PlatformInvokeGDI32.SelectObject(hMemDC, hOld);
            //We delete the memory device context.
            PlatformInvokeGDI32.DeleteDC(hMemDC);
            //We release the screen device context.
            PlatformInvokeUSER32.ReleaseDC(hwnd, hDC);
            //Image is created by Image bitmap handle and returned.
            return System.Drawing.Image.FromHbitmap(m_HBitmap);
        }
        //If m_HBitmap is null retunrn null.
        return null;