拷贝打印机dc不行，拷贝屏幕dc则可以

2010-10-25 02:11:04 187 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

win抓取屏幕弄成流数据&流数据展示一. 概念1.设备dcDC实际上是GDI内部保存的数据结构。DC与特定的显示设备（如显示器或打印机）相关。对于显示器，DC总是与显示器上的特定视窗相关。DC中的有些值是图形「属性」，这些属性定义了GDI绘图函数工作的细节。例如，对於TextOut，DC的属性确定了文字的颜色、文字的背景色、x座标和y座标映射到视窗的显示区域的方式，以及显示文字时Windows使用的字体。 MSDN的解释:一个DC... 阅读详情

......
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(); 

}