拷贝打印机dc不行，拷贝屏幕dc则可以

[fangxing0]

......
StartDoc(hDC,&doc);
StartPage(hDC);
TextOut(hDC, 0, 0, "Hello", 5);
DC2BMP(hDC, "test.bmp");
EndPage(hDC);
EndDoc(hDC);
......

if DC2BMP Function is called with ScreenDC, BMP file is OK.
if DC2BMP Function is called with PrinterDC, BMP file is not OK. BMP file is
whole white...
What's the problem?

DC2BMP(hDC, "test.bmp"）如下：

HANDLE CBitMapTestDlg::DDBToDIB(CBitmap& bitmap, DWORD dwCompression, 
CPalette* pPal) { 
BITMAP bm; 
BITMAPINFOHEADER bi; 
LPBITMAPINFOHEADER lpbi; 
DWORD dwLen; 
HANDLE hDIB; 
HANDLE handle; 
HDC hDC; 
HPALETTE hPal; 

ASSERT(bitmap.GetSafeHandle()); 

// The function has no arg for bitfields 
if(dwCompression == BI_BITFIELDS) 
return NULL; 

// If a palette has not been supplied use defaul palette 
if((hPal = (HPALETTE) pPal->GetSafeHandle()) == NULL) 
hPal = (HPALETTE) GetStockObject(DEFAULT_PALETTE); 

// Get bitmap information 
bitmap.GetObject(sizeof(bm),(LPSTR)&bm); 

// Initialize the bitmapinfoheader 
bi.biSize = sizeof(BITMAPINFOHEADER); 
bi.biWidth = bm.bmWidth; 
bi.biHeight = bm.bmHeight; 
bi.biPlanes = 1; 
bi.biBitCount = bm.bmPlanes * bm.bmBitsPixel; 
bi.biCompression = dwCompression; 
bi.biSizeImage = 0; 
bi.biXPelsPerMeter = 0; 
bi.biYPelsPerMeter = 0; 
bi.biClrUsed = 0; 
bi.biClrImportant = 0; 

// Compute the size of the infoheader and the color table 
int nColors = (1 << bi.biBitCount); 
if(nColors > 256) 
nColors = 0; 
dwLen = bi.biSize + nColors * sizeof(RGBQUAD); 
// We need a device context to get the DIB from 
hDC = ::GetDC(NULL); 
hPal = SelectPalette(hDC,hPal,FALSE); 
RealizePalette(hDC); 
// Allocate enough memory to hold bitmapinfoheader and color table 
if(!(hDIB = GlobalAlloc(GMEM_FIXED,dwLen))) { 
SelectPalette(hDC,hPal,FALSE); 
::ReleaseDC(NULL,hDC); 
return NULL; 
} 
lpbi = (LPBITMAPINFOHEADER)hDIB; 
*lpbi = bi; 

// Call GetDIBits with a NULL lpBits param, so the device driver 
// will calculate the biSizeImage field 
GetDIBits(hDC, (HBITMAP)bitmap.GetSafeHandle(), 0L, (DWORD)bi.biHeight, 
(LPBYTE)NULL, (LPBITMAPINFO)lpbi, (DWORD)DIB_RGB_COLORS); 
bi = *lpbi; 

// If the driver did not fill in the biSizeImage field, then compute it 
// Each scan line of the image is aligned on a DWORD (32bit) boundary 
if(bi.biSizeImage == 0) { 
bi.biSizeImage = ((((bi.biWidth * bi.biBitCount) + 31) & ~31) / 8) * 
bi.biHeight; 
// If a compression scheme is used the result may infact be larger 
// Increase the size to account for this. 
if(dwCompression != BI_RGB) 
bi.biSizeImage = (bi.biSizeImage * 3) / 2; 
} 
// Realloc the buffer so that it can hold all the bits 
dwLen += bi.biSizeImage; 
if(handle = GlobalReAlloc(hDIB, dwLen, GMEM_MOVEABLE)) 
hDIB = handle; 
else { 
GlobalFree(hDIB); 
// Reselect the original palette 
SelectPalette(hDC,hPal,FALSE); 
::ReleaseDC(NULL,hDC); 
return NULL; 
} 
// Get the bitmap bits 
lpbi = (LPBITMAPINFOHEADER)hDIB; 

// FINALLY get the DIB 
BOOL bGotBits = GetDIBits(hDC, (HBITMAP)bitmap.GetSafeHandle(), 0L, 
(DWORD)bi.biHeight, (LPBYTE)lpbi + (bi.biSize + nColors * sizeof(RGBQUAD)), 
(LPBITMAPINFO)lpbi, (DWORD)DIB_RGB_COLORS); // Use RGB for color table 
if(!bGotBits) { 
GlobalFree(hDIB); 
SelectPalette(hDC,hPal,FALSE); 
::ReleaseDC(NULL,hDC); 
return NULL; 
} 
SelectPalette(hDC,hPal,FALSE); 
::ReleaseDC(NULL,hDC); 
return hDIB; 
} 

// WriteDIB - Writes a DIB to file 
// Returns - TRUE on success 
// szFile - Name of file to write to 
// hDIB - Handle of the DIB 
BOOL CBitMapTestDlg::WriteDIB(LPTSTR szFile, HANDLE hDIB) { 
BITMAPFILEHEADER hdr; 
LPBITMAPINFOHEADER lpbi; 
if(!hDIB) 
return FALSE; 
CFile file; 
if(!file.Open( szFile, CFile::modeWrite|CFile::modeCreate) ) 
return FALSE; 
lpbi = (LPBITMAPINFOHEADER)hDIB; 
int nColors = 1 << lpbi->biBitCount; 
// Fill in the fields of the file header 
hdr.bfType = ((WORD) ('M' << 8) | 'B'); // is always "BM" 
hdr.bfSize = DWORD(GlobalSize(hDIB) + sizeof(hdr)); 
hdr.bfReserved1 = 0; 
hdr.bfReserved2 = 0; 
hdr.bfOffBits = (DWORD) (sizeof( hdr ) + lpbi->biSize + nColors * 
sizeof(RGBQUAD)); 
// Write the file header 
file.Write(&hdr, sizeof(hdr)); 
// Write the DIB header and the bits 
file.Write(lpbi, (UINT)GlobalSize(hDIB)); 
return TRUE; 
} 



void CBitMapTestDlg::DC2BMP(HDC hdc, char* filename) { 
CDC srcDC, memDC; 
CBitmap bitmap, *pbitmap=NULL; 
srcDC.Attach(hdc); 
memDC.CreateCompatibleDC(&srcDC); 
bitmap.CreateCompatibleBitmap(&srcDC, srcDC.GetDeviceCaps(HORZRES), 
srcDC.GetDeviceCaps(VERTRES)); 
pbitmap = memDC.SelectObject(&bitmap); 
memDC.BitBlt(0, 0, srcDC.GetDeviceCaps(HORZRES), 
srcDC.GetDeviceCaps(VERTRES), &srcDC, 0, 0, SRCCOPY); 
HANDLE hDIB = DDBToDIB(bitmap, BI_RGB, NULL); 
WriteDIB(filename, hDIB); 
srcDC.Detach(); 
} 

[xhjbeidoulong]

应该得不到吧?
对GDI的调用,都传给了打印驱动,在内存并没有相应内存数据.
你只有也虚拟打印机,才能获得对应的图片.

[fangxing0]

[Quote=引用 1 楼 xhjbeidoulong 的回复:]
应该得不到吧?
对GDI的调用,都传给了打印驱动,在内存并没有相应内存数据.
你只有也虚拟打印机,才能获得对应的图片.
[/Quote]
能在详细点不？谢谢

[fangxing0]

[Quote=引用 3 楼 xhjbeidoulong 的回复:]
在往屏幕DC作图时, 所有图像数据是存在内存的, 所以你能得到图像.
往打印DC作图时, 对GDI的调用会全部转换成打印驱动API的调用, 你能否得到图像依赖于驱动的实现.

通常我们的做法时, 写个虚拟打印机(实现打印驱动), 输出的图像数据转存在文件.
至于实现虚拟打印机, 不是一两句话就说得清楚, 请在网上查找相关资料.
[/Quote]
清楚些了，谢谢。

[xhjbeidoulong]

在往屏幕DC作图时, 所有图像数据是存在内存的, 所以你能得到图像.
往打印DC作图时, 对GDI的调用会全部转换成打印驱动API的调用, 你能否得到图像依赖于驱动的实现.

通常我们的做法时, 写个虚拟打印机(实现打印驱动), 输出的图像数据转存在文件.
至于实现虚拟打印机, 不是一两句话就说得清楚, 请在网上查找相关资料.