Screen capture code produces black bitmap
- by wadetandy
I need to add the ability to take a screenshot of the entire screen, not just the current window. The following code produces a bmp file with the correct dimensions, but the image is completely black. What am I doing wrong?
void CaptureScreen(LPCTSTR lpszFilePathName)
{
BITMAPFILEHEADER bmfHeader;
BITMAPINFO *pbminfo;
HBITMAP hBmp;
FILE *oFile;
HDC screen;
HDC memDC;
int sHeight;
int sWidth;
LPBYTE pBuff;
BITMAP bmp;
WORD cClrBits;
RECT rcClient;
screen = GetDC(0);
memDC = CreateCompatibleDC(screen);
sHeight = GetDeviceCaps(screen, VERTRES);
sWidth = GetDeviceCaps(screen, HORZRES);
//GetObject(screen, sizeof(BITMAP), &bmp);
hBmp = CreateCompatibleBitmap ( screen, sWidth, sHeight );
// Retrieve the bitmap color format, width, and height.
GetObject(hBmp, sizeof(BITMAP), (LPSTR)&bmp) ;
// Convert the color format to a count of bits.
cClrBits = (WORD)(bmp.bmPlanes * bmp.bmBitsPixel);
if (cClrBits == 1)
cClrBits = 1;
else if (cClrBits bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
pbminfo-bmiHeader.biWidth = bmp.bmWidth;
pbminfo-bmiHeader.biHeight = bmp.bmHeight;
pbminfo-bmiHeader.biPlanes = bmp.bmPlanes;
pbminfo-bmiHeader.biBitCount = bmp.bmBitsPixel;
if (cClrBits bmiHeader.biClrUsed = (1bmiHeader.biCompression = BI_RGB;
// Compute the number of bytes in the array of color
// indices and store the result in biSizeImage.
// The width must be DWORD aligned unless the bitmap is RLE
// compressed.
pbminfo-bmiHeader.biSizeImage = ((pbminfo-bmiHeader.biWidth * cClrBits +31) & ~31) /8
* pbminfo-bmiHeader.biHeight;
// Set biClrImportant to 0, indicating that all of the
// device colors are important.
pbminfo-bmiHeader.biClrImportant = 0;
CreateBMPFile(lpszFilePathName, pbminfo, hBmp, memDC);
}
void CreateBMPFile(LPTSTR pszFile, PBITMAPINFO pbi,
HBITMAP hBMP, HDC hDC)
{
HANDLE hf; // file handle
BITMAPFILEHEADER hdr; // bitmap file-header
PBITMAPINFOHEADER pbih; // bitmap info-header
LPBYTE lpBits; // memory pointer
DWORD dwTotal; // total count of bytes
DWORD cb; // incremental count of bytes
BYTE *hp; // byte pointer
DWORD dwTmp;
int lines;
pbih = (PBITMAPINFOHEADER) pbi;
lpBits = (LPBYTE) GlobalAlloc(GMEM_FIXED, pbih-biSizeImage);
// Retrieve the color table (RGBQUAD array) and the bits
// (array of palette indices) from the DIB.
lines = GetDIBits(hDC, hBMP, 0, (WORD) pbih-biHeight, lpBits, pbi,
DIB_RGB_COLORS);
// Create the .BMP file.
hf = CreateFile(pszFile,
GENERIC_READ | GENERIC_WRITE,
(DWORD) 0,
NULL,
CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL,
(HANDLE) NULL);
hdr.bfType = 0x4d42; // 0x42 = "B" 0x4d = "M"
// Compute the size of the entire file.
hdr.bfSize = (DWORD) (sizeof(BITMAPFILEHEADER) +
pbih-biSize + pbih-biClrUsed
* sizeof(RGBQUAD) + pbih-biSizeImage);
hdr.bfReserved1 = 0;
hdr.bfReserved2 = 0;
// Compute the offset to the array of color indices.
hdr.bfOffBits = (DWORD) sizeof(BITMAPFILEHEADER) +
pbih-biSize + pbih-biClrUsed
* sizeof (RGBQUAD);
// Copy the BITMAPFILEHEADER into the .BMP file.
WriteFile(hf, (LPVOID) &hdr, sizeof(BITMAPFILEHEADER),
(LPDWORD) &dwTmp, NULL);
// Copy the BITMAPINFOHEADER and RGBQUAD array into the file.
WriteFile(hf, (LPVOID) pbih, sizeof(BITMAPINFOHEADER)
+ pbih-biClrUsed * sizeof (RGBQUAD),
(LPDWORD) &dwTmp, ( NULL));
// Copy the array of color indices into the .BMP file.
dwTotal = cb = pbih-biSizeImage;
hp = lpBits;
WriteFile(hf, (LPSTR) hp, (int) cb, (LPDWORD) &dwTmp,NULL);
// Close the .BMP file.
CloseHandle(hf);
// Free memory.
GlobalFree((HGLOBAL)lpBits);
}
