在 C# 中读取打印机设备上下文

Question

我能够显示屏幕设备并将其保存到 DIB 位图，并且我想对打印机设备上下文执行相同的操作。我可以得到一个非空位图，但它总是纯黑色。

这是允许我处理屏幕设备上下文的代码。

        //In size variable we shall keep the size of the window.
        SIZE size;

        //Win32 API functions are imported in classes
        //PlatformInvokeGDI32
        //PlatformInvokeUSER32

        //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();

        //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;

这是我获取打印机设备上下文的方法：

        //In size variable we shall keep the size of the window.
        SIZE size;
        size.cx = 1000;
        size.cy = 1000;

        //Get Printer Handle
        IntPtr PrinterHandle;
        PlatformInvokeGDI32.PRINTER_DEFAULTSW defaults = new PlatformInvokeGDI32.PRINTER_DEFAULTSW();
        PlatformInvokeGDI32.OpenPrinterW("Bullzip PDF Printer", out PrinterHandle, defaults);

        //Get Printer Device context
        IntPtr PrinterHDC = PlatformInvokeGDI32.CreateDCW("", "Bullzip PDF Printer", "", IntPtr.Zero);

        //Initialize DocInfo structure.
        PlatformInvokeGDI32.DOCINFOW docInfo = new PlatformInvokeGDI32.DOCINFOW();

        //Start printing.
        PlatformInvokeGDI32.StartDocW(PrinterHDC, ref docInfo);
        PlatformInvokeGDI32.StartPage(PrinterHDC);
        Graphics graphics = Graphics.FromHdc(PrinterHDC, PrinterHandle);

        Color theColor = Color.FromName("Red");
        Pen pen = new Pen(theColor);
        graphics.DrawRectangle(pen, 50, 50, 50, 50);
        graphics.DrawEllipse(pen, 50, 50, 50, 50);
        graphics.Save();

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

        //Create a compatible bitmap of window size and using screen device context.
        m_HBitmap = PlatformInvokeGDI32.CreateCompatibleBitmap(PrinterHDC, 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, PrinterHDC, 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, PrinterHDC);
            //Image is created by Image bitmap handle and returned.

            PlatformInvokeGDI32.EndPage(PrinterHDC);
            PlatformInvokeGDI32.EndDoc(PrinterHDC);
            PlatformInvokeGDI32.ClosePrinter(PrinterHandle);
            pen.Dispose();
            graphics.Dispose();


            return System.Drawing.Image.FromHbitmap(m_HBitmap);
        }
        //If m_HBitmap is null retunrn null.
        return null;

如何使用打印机设备上下文？ 如何将打印机设备上下文保存到 DIB？

谢谢，

雅各布

Answer 1

打印机设备上下文是只写的。

例如，假设您要打印到 PostScript 打印机。您创建一个打印机设备上下文并在其上绘制一些文本。打印机设备驱动程序不会呈现包含您的文本的位图。相反，它会创建一系列 PostScript 命令来绘制文本并将命令发送到打印机。换句话说，没有要复制的位图。

你想达到什么目的？