| Introduction |
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The guts of this code is basic Windows programming, the clever part is saving to a BMP on disk then converting the BMP to JPG using custom code taken from www.codeproject.com .
The code uses a few custom classes for saving and converting from BMP to JPG, to do this see http://www.codeproject.com/KB/graphics/cximage.aspx . The code to save a BMP to a file is below. Take it, make it your own.
The main function is ScreenCapture() which I put in CMainFrame.
class CSaveBitmapToFile
{
public:
CSaveBitmapToFile();
virtual ~CSaveBitmapToFile();
PBITMAPINFO CreateBitmapInfoStruct(CWnd*, HBITMAP hBmp);
void CreateBMPFile(CWnd*, LPCTSTR pszFile, PBITMAPINFO pbi, HBITMAP hBMP, HDC hDC);
};
//////////////////////////////////////////////////////////////////////
// Construction/Destruction
//////////////////////////////////////////////////////////////////////
CSaveBitmapToFile::CSaveBitmapToFile()
{
}
CSaveBitmapToFile::~CSaveBitmapToFile()
{
}
//
// Create structures.
//
PBITMAPINFO CSaveBitmapToFile::CreateBitmapInfoStruct(CWnd* pParent, HBITMAP hBmp)
{
BITMAP bmp = {0};
PBITMAPINFO pbmi = NULL;
WORD cClrBits = 0;
//
// Retrieve the bitmap's color format, width, and height.
//
if (!::GetObject(hBmp, sizeof(BITMAP), (LPSTR)&bmp))
{
CErrorText err;
CString strText;
strText.Format(_T("Error getting bitmap colour format, width and height: %s"), err.Text());
pParent->MessageBox(strText, _T("Error"), MB_OK | MB_ICONERROR);
return NULL;
}
//
// Convert the color format to a count of bits.
//
cClrBits = (WORD)(bmp.bmPlanes * bmp.bmBitsPixel);
if (cClrBits == 1)
cClrBits = 1;
else if (cClrBits <= 4)
cClrBits = 4;
else if (cClrBits <= 8)
cClrBits = 8;
else if (cClrBits <= 16)
cClrBits = 16;
else if (cClrBits <= 24)
cClrBits = 24;
else cClrBits = 32;
//
// Allocate memory for the BITMAPINFO structure. (This structure
// contains a BITMAPINFOHEADER structure and an array of RGBQUAD
// data structures.)
//
if (cClrBits != 24)
{
pbmi = (PBITMAPINFO)LocalAlloc(LPTR, sizeof(BITMAPINFOHEADER) + sizeof(RGBQUAD) * (1 << cClrBits));
}
//
// There is no RGBQUAD array for the 24-bit-per-pixel format.
//
else
{
pbmi = (PBITMAPINFO)LocalAlloc(LPTR, sizeof(BITMAPINFOHEADER));
}
//
// Initialize the fields in the BITMAPINFO structure.
///
pbmi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
pbmi->bmiHeader.biWidth = bmp.bmWidth;
pbmi->bmiHeader.biHeight = bmp.bmHeight;
pbmi->bmiHeader.biPlanes = bmp.bmPlanes;
pbmi->bmiHeader.biBitCount = bmp.bmBitsPixel;
if (cClrBits < 24)
pbmi->bmiHeader.biClrUsed = (1 << cClrBits);
//
// If the bitmap is not compressed, set the BI_RGB flag.
//
pbmi->bmiHeader.biCompression = BI_RGB;
//
// Compute the number of bytes in the array of color
// indices and store the result in biSizeImage.
// For Windows NT/2000, the width must be DWORD aligned unless
// the bitmap is RLE compressed. This example shows this.
// For Windows 95/98, the width must be WORD aligned unless the
// bitmap is RLE compressed.
//
pbmi->bmiHeader.biSizeImage = ((pbmi->bmiHeader.biWidth * cClrBits + 31) & ~31) / 8 * pbmi->bmiHeader.biHeight;
//
// Set biClrImportant to 0, indicating that all of the
// device colors are important.
//
pbmi->bmiHeader.biClrImportant = 0;
return pbmi;
}
//
// The following example code defines a function that initializes the remaining structures,
// retrieves the array of palette indices, opens the file, copies the data, and closes the file.
//
void CSaveBitmapToFile::CreateBMPFile(CWnd* pParent,
LPCTSTR pszFile,
PBITMAPINFO pbi,
HBITMAP hBMP,
HDC hDC)
{
HANDLE hf = NULL; // File handle
BITMAPFILEHEADER hdr = {0}; // Bitmap file-header
PBITMAPINFOHEADER pbih = NULL; // Bitmap info-header
LPBYTE lpBits = NULL; // Memory pointer
DWORD dwTotal = 0; // Total count of bytes
DWORD cb = 0; // Incremental count of bytes
BYTE* hp = NULL; // Byte pointer
DWORD dwTmp = 0;
pbih = (PBITMAPINFOHEADER) pbi;
lpBits = (LPBYTE)GlobalAlloc(GMEM_FIXED, pbih->biSizeImage);
if (!lpBits)
{
pParent->MessageBox(_T("Error allocating temporary storage."),
_T("Error"),
MB_OK | MB_ICONERROR);
return;
}
//
// Retrieve the color table (RGBQUAD array) and the bits
// (array of palette indices) from the DIB.
//
if (!GetDIBits(hDC, hBMP, 0, (WORD) pbih->biHeight, lpBits, pbi, DIB_RGB_COLORS))
{
pParent->MessageBox(_T("Error retrieving colour table and bits."),
_T("Error"),
MB_OK | MB_ICONERROR);
GlobalFree((HGLOBAL)lpBits);
return;
}
//
// Create the .BMP file.
//
hf = CreateFile(pszFile,
GENERIC_READ | GENERIC_WRITE,
(DWORD)0,
NULL,
CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL,
(HANDLE) NULL);
if (hf == INVALID_HANDLE_VALUE)
{
CString strText;
CErrorText error;
strText.Format(_T("Error creating output file: %s -\n%s"),
pszFile,
error.Text());
pParent->MessageBox(strText,
_T("Error"),
MB_OK | MB_ICONERROR);
GlobalFree((HGLOBAL)lpBits);
return;
}
//
// BM 0x42 = "B" 0x4d = "M".
//
hdr.bfType = 0x4d42;
//
// 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.
//
if (!WriteFile(hf,
(LPVOID)&hdr,
sizeof(BITMAPFILEHEADER),
(LPDWORD) &dwTmp, NULL))
{
pParent->MessageBox(_T("Error writing to output file."),
_T("Error"),
MB_OK | MB_ICONERROR);
GlobalFree((HGLOBAL)lpBits);
CloseHandle(hf);
return;
}
//
// Copy the BITMAPINFOHEADER and RGBQUAD array into the file.
//
if (!WriteFile(hf,
(LPVOID)pbih,
sizeof(BITMAPINFOHEADER) + pbih->biClrUsed * sizeof (RGBQUAD),
(LPDWORD)&dwTmp,
(NULL)))
{
pParent->MessageBox(_T("Error writing to output file."),
_T("Error"),
MB_OK | MB_ICONERROR);
GlobalFree((HGLOBAL)lpBits);
CloseHandle(hf);
return;
}
//
// Copy the array of color indices into the .BMP file.
//
dwTotal = cb = pbih->biSizeImage;
hp = lpBits;
if (!WriteFile(hf,
(LPSTR)hp,
(int)cb,
(LPDWORD)&dwTmp,
NULL))
{
pParent->MessageBox(_T("Error writing to output file."),
_T("Error"),
MB_OK | MB_ICONERROR);
GlobalFree((HGLOBAL)lpBits);
CloseHandle(hf);
return;
}
//
// Close the .BMP file.
//
CloseHandle(hf);
//
// Free memory.
//
GlobalFree((HGLOBAL)lpBits);
}
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