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VC++ MFC Sample: CreateDIBSection, BITMAPINFOHEADER, CreateCompatibleDC, BITMAPINFO

 
 By Arun krishnan. 

Download demo project - 147 Kb


Introduction

This article describes a simple calendar that sits on your desktop. I have created this application to just study about alpha blending, desktop wallpapers, and how a device context can be saved as a bitmap. I am planning to make a more refined version including a time scheduler and reminder also.

Using the code

Alpha Blending

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HBITMAP Create24BPPDIBSection(HDC hDC, int iWidth, int iHeight)
{
    BITMAPINFO bmi;
    HBITMAP hbm;
    LPBYTE pBits;

    // Initialize header to 0s.
    ZeroMemory(&bmi, sizeof(bmi));

    // Fill out the fields you care about.
    bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    bmi.bmiHeader.biWidth = iWidth;
    bmi.bmiHeader.biHeight = iHeight;
    bmi.bmiHeader.biPlanes = 1;
    bmi.bmiHeader.biBitCount = 24;
    bmi.bmiHeader.biCompression = BI_RGB;

    // Create the surface.
    hbm = CreateDIBSection(hDC, &bmi, DIB_RGB_COLORS,(void **)&pBits, NULL, 0);
      
    return(hbm);
}

BOOL BitmapsCompatible(LPBITMAP lpbm1, LPBITMAP lpbm2)
{
    if (lpbm1->bmBitsPixel != lpbm2->bmBitsPixel) 
        return FALSE;
    if (lpbm1->bmPlanes    != lpbm2->bmPlanes)    
        return FALSE;
    if (lpbm1->bmWidth     != lpbm2->bmWidth)     
        return FALSE;
    if (lpbm1->bmHeight    != lpbm2->bmHeight)    
        return FALSE;
    return TRUE;
}

BOOL BlendImages(HBITMAP hbmSrc1, HBITMAP hbmSrc2, HBITMAP hbmDst, DWORD dwWeight1)
{
    BITMAP bmSrc1, bmSrc2, bmDst;
    RGBTRIPLE *lprgbSrc1, *lprgbSrc2, *lprgbDst;
    DWORD dwWidthBytes, dwWeight2;
    int x, y;
    
    // Only values between 0 and 255 are valid.
    if (dwWeight1 > 255) return FALSE;
    
    // Get weighting value for second source image.
    dwWeight2 = 255-dwWeight1;
    
    // Get information about the surfaces you were passed.
    if (!GetObject(hbmSrc1, sizeof(BITMAP), &bmSrc1)) return FALSE;
    if (!GetObject(hbmSrc2, sizeof(BITMAP), &bmSrc2)) return FALSE;
    if (!GetObject(hbmDst,  sizeof(BITMAP), &bmDst))  return FALSE;

    // Make sure you have data that meets your requirements.
    if (!BitmapsCompatible(&bmSrc1, &bmSrc2))
        return FALSE;
    if (!BitmapsCompatible(&bmSrc1, &bmDst))
        return FALSE;
    if (bmSrc1.bmBitsPixel != 24)
        return FALSE;
    if (bmSrc1.bmPlanes != 1)
        return FALSE;
    if (!bmSrc1.bmBits || !bmSrc2.bmBits || !bmDst.bmBits)
        return FALSE;

    dwWidthBytes = bmDst.bmWidthBytes;
    
    // Initialize the surface pointers.
    lprgbSrc1 = (RGBTRIPLE *)bmSrc1.bmBits; 
    lprgbSrc2 = (RGBTRIPLE *)bmSrc2.bmBits;  
    lprgbDst  = (RGBTRIPLE *)bmDst.bmBits;

    for (y=0; y<bmDst.bmHeight; y++) {
        for (x=0; x<bmDst.bmWidth; x++) {
            lprgbDst[x].rgbtRed   = 
              (BYTE)((((DWORD)lprgbSrc1[x].rgbtRed * dwWeight1) + 
              ((DWORD)lprgbSrc2[x].rgbtRed * dwWeight2)) >> 8);
            lprgbDst[x].rgbtGreen = 
              (BYTE)((((DWORD)lprgbSrc1[x].rgbtGreen * dwWeight1) + 
              ((DWORD)lprgbSrc2[x].rgbtGreen * dwWeight2)) >> 8);
            lprgbDst[x].rgbtBlue  = 
              (BYTE)((((DWORD)lprgbSrc1[x].rgbtBlue * dwWeight1) + 
              ((DWORD)lprgbSrc2[x].rgbtBlue * dwWeight2)) >> 8);
        }

        // Move to next scan line.
        lprgbSrc1 = (RGBTRIPLE *)((LPBYTE)lprgbSrc1 + dwWidthBytes);
        lprgbSrc2 = (RGBTRIPLE *)((LPBYTE)lprgbSrc2 + dwWidthBytes);
        lprgbDst  = (RGBTRIPLE *)((LPBYTE)lprgbDst  + dwWidthBytes);
    }

    return TRUE;
}

BOOL DoAlphaBlend(
  HDC hdcDest,                 // Handle to destination DC.
  int nXOriginDest,            // X-coord of upper-left corner.
  int nYOriginDest,            // Y-coord of upper-left corner.
  int nWidthDest,              // Destination width.
  int nHeightDest,             // Destination height.
  HDC hdcSrc,                  // Handle to source DC.
  int nXOriginSrc,             // X-coord of upper-left corner.
  int nYOriginSrc,             // Y-coord of upper-left corner.
  int nWidthSrc,               // Source width.
  int nHeightSrc,              // Source height.
  DWORD dwSourceWeight)        // Source weighting (between 0 and 255).
{
    HDC      hdcSrc1 = NULL;
    HDC      hdcSrc2 = NULL;
    HDC      hdcDst  = NULL;
    HBITMAP  hbmSrc1 = NULL;
    HBITMAP  hbmSrc2 = NULL;
    HBITMAP  hbmDst  = NULL;
    BOOL     bReturn;

    // Create surfaces for sources and destination images.
    hbmSrc1 = Create24BPPDIBSection(hdcDest, nWidthDest,nHeightDest);
    if (!hbmSrc1) goto HANDLEERROR;

    hbmSrc2 = Create24BPPDIBSection(hdcDest, nWidthDest,nHeightDest);
    if (!hbmSrc2) goto HANDLEERROR;

    hbmDst  = Create24BPPDIBSection(hdcDest, nWidthDest,nHeightDest);
    if (!hbmDst) goto HANDLEERROR;

    
    // Create HDCs to hold our surfaces.
    hdcSrc1 = CreateCompatibleDC(hdcDest);
    if (!hdcSrc1) goto HANDLEERROR;
    
    hdcSrc2 = CreateCompatibleDC(hdcDest);
    if (!hdcSrc2) goto HANDLEERROR;
    
    hdcDst  = CreateCompatibleDC(hdcDest);
    if (!hdcDst) goto HANDLEERROR;

    
    // Prepare the surfaces for drawing.
    SelectObject(hdcSrc1, hbmSrc1);
    SelectObject(hdcSrc2, hbmSrc2);
    SelectObject(hdcDst,  hbmDst);
    SetStretchBltMode(hdcSrc1, COLORONCOLOR);
    SetStretchBltMode(hdcSrc2, COLORONCOLOR);

    
    // Capture a copy of the source area.
    if (!StretchBlt(hdcSrc1, 0,0,nWidthDest,nHeightDest,
                    hdcSrc,  nXOriginSrc, nYOriginSrc, nWidthSrc, nHeightSrc, 
                    SRCCOPY))
         goto HANDLEERROR;
    
    // Capture a copy of the destination area.
    if (!StretchBlt(hdcSrc2, 0,0,nWidthDest,nHeightDest,
                    hdcDest, nXOriginDest, nYOriginDest, nWidthDest, nHeightDest, 
                    SRCCOPY))
         goto HANDLEERROR;

                  
    // Blend the two source areas to create the destination image.
    bReturn = BlendImages(hbmSrc1, hbmSrc2, hbmDst, dwSourceWeight);

    
    // Clean up objects you do not need any longer.
    // You cannot delete an object that's selected into an
    // HDC so delete the HDC first. 
    DeleteDC(hdcSrc1);
    DeleteDC(hdcSrc2);
    DeleteObject(hbmSrc1);
    DeleteObject(hbmSrc2);

    
    // Display the blended (destination) image to the target HDC.
    if (bReturn) {
        BitBlt(hdcDest, nXOriginDest, nYOriginDest, nWidthDest, nHeightDest, 
               hdcDst, 0,0, SRCCOPY);
    }

    
    // Clean up the rest of the objects you created.
    DeleteDC(hdcDst);
    DeleteObject(hbmDst);

    return bReturn;

HANDLEERROR:

    if (hdcSrc1) DeleteDC(hdcSrc1);
    if (hdcSrc2) DeleteDC(hdcSrc2);
    if (hdcDst)  DeleteDC(hdcDst);
    if (hbmSrc1) DeleteObject(hbmSrc1);
    if (hbmSrc2) DeleteObject(hbmSrc2);
    if (hbmDst)  DeleteObject(hbmDst);

    return FALSE;
}

Save Device Context into an uncompressed bitmap

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// Function to save bitmap
BOOL SaveBitmap(HDC hDC,HBITMAP hBitmap,CString szPath)
{
    FILE * fp= NULL;
    fp = fopen(szPath.GetBuffer(1),"wb");
    if(fp == NULL)
        return false;
    
    BITMAP Bm;
    BITMAPINFO BitInfo;
    ZeroMemory(&BitInfo, sizeof(BITMAPINFO));
    BitInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    BitInfo.bmiHeader.biBitCount = 0;

    if(!::GetDIBits(hDC, hBitmap, 0, 0, NULL, &BitInfo, DIB_RGB_COLORS))
        return (false);

    Bm.bmHeight = BitInfo.bmiHeader.biHeight;
    Bm.bmWidth  = BitInfo.bmiHeader.biWidth;

    BITMAPFILEHEADER    BmHdr;
    
    BmHdr.bfType        = 0x4d42;   // 'BM' WINDOWS_BITMAP_SIGNATURE
    BmHdr.bfSize        = (((3 * Bm.bmWidth + 3) & ~3) * Bm.bmHeight) 
                          + sizeof(BITMAPFILEHEADER) 
                          + sizeof(BITMAPINFOHEADER);
    BmHdr.bfReserved1    = BmHdr.bfReserved2 = 0;
    BmHdr.bfOffBits      = (DWORD) sizeof(BITMAPFILEHEADER) 
                          + sizeof(BITMAPINFOHEADER);
    
    BitInfo.bmiHeader.biCompression = 0;
    // Writing Bitmap File Header ////
    fwrite(&BmHdr,sizeof(BITMAPFILEHEADER),1,fp);

    fwrite(&BitInfo.bmiHeader,sizeof(BITMAPINFOHEADER),1,fp);

    BYTE *pData = new BYTE[BitInfo.bmiHeader.biSizeImage + 5];
    if(!::GetDIBits(hDC, hBitmap, 0, Bm.bmHeight, 
                 pData, &BitInfo, DIB_RGB_COLORS))
        return (false);
    if(pData != NULL)
        fwrite(pData,1,BitInfo.bmiHeader.biSizeImage,fp);

    fclose(fp);
    delete (pData);

    return (true);
}

// here is how to use the above function

//Get the device context
HDC hDC = ::GetDC(hWnd);
// Create a memory device context
HDC hMemDC = ::CreateCompatibleDC(hDC);
// Create a compatible bitmap 
HBITMAP hBitmap = CreateCompatibleBitmap(hDC, 
                 nScreenWidth,nScreenHeight);
// Select the bitmap into the memory context
::SelectObject(hMemDC,hBitmap);    
// Do what ever drawing you want into the Device Context
...
...
SaveBitmap(hMemDC, hBitmap,"Sample.bmp");

Points of Interest

SetStretchBltMode(hDC,HALFTONE)

Try out this function, this improves the quality of StretchBlt(). I think with our using this mode, SretchBlt() function cannot give you the required quality if you are dealing with big bitmaps.

 

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