朋友说在一个VC++6.0开发的项目中要增加打印窗体的功能，让帮忙写个代码供其调用。

这么老的IDE当然不想碰了，并且也不喜欢MFC笨拙不清晰的封装。所以决定採用纯Win32 API，然后用C++类简单封装一下。

1 基本思路

窗体DC和打印机DC是两类不兼容的DC。所以它们之间传送位图仅仅能通过DIB。首先，通过BitBlt()把要打印窗体的客户区复制到DDB内存位图中，然后通过GetDIBits()把DDB转换为DIB，最后通过StretchDIBits()向打印机DC输出。

2 代码实现

头文件 WinowPrinter.h

#pragma once

/********************************************************************************

                         WindowPrinter 打印窗体类

功能描写叙述：

提供截屏窗体并通过默认打印机，自己主动进行居中缩放打印

使用说明：

例子代码例如以下。

	HWND hwnd = this->GetSafeWnd();

	WindowPrinter::PrintWindowClientArea(hwnd);

********************************************************************************/

class WindowPrinter

{

public:

	WindowPrinter();

	~WindowPrinter();

public:

	/*

	功能：获取当前默认打印机的DC

	返回：成功返回打印机的DC，失败返回NULL

	*/

	static HDC GetPrinterDC();

	/*

	功能：打印窗体客户区内容到打印机。自己主动缩放居中打印

	參数: hWnd-被打印窗体的句柄

	*/

	static void PrintWindowClientArea(HWND hwnd);

};

实现文件 WindowPrinter.cpp

#include "stdafx.h"

#include "WindowPrinter.h"

#include <Winspool.h>

WindowPrinter::WindowPrinter()

{

}

WindowPrinter::~WindowPrinter()

{

}

/*

功能：获取当前默认打印机的DC

返回：成功返回打印机的DC。失败返回NULL

*/

HDC WindowPrinter::GetPrinterDC()

{

	DWORD dwNeeded, dwReturned;

	HDC hdc;

	::EnumPrinters(PRINTER_ENUM_LOCAL, NULL, 4, NULL, 0, &dwNeeded, &dwReturned);

	PRINTER_INFO_4* pinfo4 = (PRINTER_INFO_4*)malloc(dwNeeded);

	::EnumPrinters(PRINTER_ENUM_LOCAL, NULL, 4, (BYTE*)pinfo4, dwNeeded, &dwNeeded, &dwReturned);

	hdc = ::CreateDC(NULL, pinfo4->pPrinterName, NULL, NULL);

	free(pinfo4);

	return hdc;

}

/*

功能：打印窗体客户区内容到打印机，自己主动缩放居中打印

參数: hWnd-被打印窗体的句柄

*/

void WindowPrinter::PrintWindowClientArea(HWND hWnd)

{

	if (hWnd == NULL) return;

	RECT rectClient;

	::GetClientRect(hWnd, &rectClient);

	int width = rectClient.right - rectClient.left;

	int height = rectClient.bottom - rectClient.top;

	// 通过内存DC复制客户区到DDB位图

	HDC hdcWnd = ::GetDC(hWnd);

	HBITMAP hbmWnd = ::CreateCompatibleBitmap(hdcWnd, width, height);

	HDC hdcMem = ::CreateCompatibleDC(hdcWnd);

	::SelectObject(hdcMem, hbmWnd);

	::BitBlt(hdcMem, 0, 0, width, height, hdcWnd, 0, 0, SRCCOPY);

	// 把窗体DDB转为DIB

	BITMAP bmpWnd;

	::GetObject(hbmWnd, sizeof(BITMAP), &bmpWnd);

	BITMAPINFOHEADER bi; // 信息头

	bi.biSize = sizeof(BITMAPINFOHEADER);

	bi.biWidth = bmpWnd.bmWidth;

	bi.biHeight = bmpWnd.bmHeight;

	bi.biPlanes = 1;

	bi.biBitCount = 32; // 依照每一个像素用32bits表示转换

	bi.biCompression = BI_RGB;

	bi.biSizeImage = 0;

	bi.biXPelsPerMeter = 0;

	bi.biYPelsPerMeter = 0;

	bi.biClrUsed = 0;

	bi.biClrImportant = 0;

	DWORD dwBmpSize = ((bmpWnd.bmWidth * bi.biBitCount + 31) / 32) * 4 * bmpWnd.bmHeight; // 每一行像素位32对齐

	char *lpbitmap = (char*)malloc(dwBmpSize); // 像素位指针

	::GetDIBits(hdcMem, hbmWnd, 0, (UINT)bmpWnd.bmHeight,

		lpbitmap,

		(BITMAPINFO*)&bi,

		DIB_RGB_COLORS);

	::DeleteDC(hdcMem);

	::DeleteObject(hbmWnd);

	::ReleaseDC(hWnd, hdcWnd);

	// 存为文件（可选）

	BITMAPFILEHEADER bmfHeader; // 文件头

	DWORD dwSizeofDIB = dwBmpSize + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

	bmfHeader.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER) + (DWORD)sizeof(BITMAPINFOHEADER);

	bmfHeader.bfSize = dwSizeofDIB;

	bmfHeader.bfType = 0x4D42;

	FILE* fp = NULL;

	::_wfopen_s(&fp, L"capture.bmp", L"w");

	::fwrite(&bmfHeader, sizeof(BITMAPFILEHEADER), 1, fp); // 写入文件头

	::fwrite(&bi, sizeof(BITMAPINFOHEADER), 1, fp);        // 写入信息头

	::fwrite(lpbitmap, dwBmpSize, 1, fp);                  // 写入像素位

	::fclose(fp);

	fp = NULL;

	// StretchDIBits()缩放打印DIB

	HDC hdcPrinter = WindowPrinter::GetPrinterDC();

	if (hdcPrinter == NULL)

		return;

	int pageWidth = ::GetDeviceCaps(hdcPrinter, HORZRES);

	int pageHeight = ::GetDeviceCaps(hdcPrinter, VERTRES);

	float scaleX = (float)pageWidth / (float)bmpWnd.bmWidth;

	float scaleY = (float)pageHeight / (float)bmpWnd.bmHeight;

	float scale = scaleX < scaleY ?

scaleX : scaleY;

	int xDst, yDst, cxDst, cyDst;

	cxDst = (int)((float)bmpWnd.bmWidth * scale);

	cyDst = (int)((float)bmpWnd.bmHeight * scale);

	xDst = (int)((pageWidth - cxDst) / 2);

	yDst = (int)((pageHeight - cyDst) / 2);

	static DOCINFO di = { sizeof(DOCINFO), L"PRINTJOBNAME" };

	if (::StartDoc(hdcPrinter, &di) > 0)

	{

		if (::StartPage(hdcPrinter) > 0)

		{

			::StretchDIBits(hdcPrinter,

				xDst, yDst, cxDst, cyDst,

				0, 0, bmpWnd.bmWidth, bmpWnd.bmHeight,

				lpbitmap,

				(BITMAPINFO*)&bi,

				DIB_RGB_COLORS,

				SRCCOPY);

			::EndPage(hdcPrinter);

		}

		::EndDoc(hdcPrinter);

	}

	::DeleteDC(hdcPrinter);

	::free(lpbitmap);

}