Creating a 24-Bit Per Pixel Subregion of a 24-Bit Per Pixel Bitmap

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Subregion of the original bitmap

Environment: VC6

This article shows you how to create a portion of a 24-bit/pixel bitmap at runtime. In order to do this, you must add a 24-bit/pixel bitmap to your resources in VC++, decide what portion of the bitmap you wish (specified by the x-y coordinates of the upper left corner and the horizontal/vertical size of the portion), and what .bmp file you want the new portion of the bitmap to be store. The .bmp file created can be used at a later time, but in addition the bitmap of the subregion can be retrieved and used, for example, in your OnDraw function.

In the following code sample, we create a portion of a huge bitmap. The subregion is 416 by 224 pixels, but the original bitmap is well over 100 times this size.

CBitmapSubRegion bsr;
BOOL bSuccess;
// IDB_BITMAP_SCHUMACHERCAR is a 24-bit/pixel 
// resource ID added to VC++
bSuccess = bsr.SetResourceID(IDB_BITMAP_SCHUMACHERCAR);
if (bSuccess)
{
  bSuccess = bsr.SetFileNameOfResourceBitmap(
                          CString("SchumacherCar.bmp"));
  if (bSuccess)
  {
    // Want to create a subregion which starts at 
    // (x,y) of (259,317) and is 416-pixels wide by 
    // 224-pixels tall
    bSuccess = bsr.SetSubRegionOfBitmap(259,317,416,224);
    if (bSuccess)
    {
      //Set where to store the new bitmap
      bSuccess = bsr.SetFileNameForNewBitmap(
                    CString("SuhumacherCarSubRegion.bmp"));
      if (bSuccess)
      {
        bSuccess = bsr.CreateBitmapOfSubRegion();
        if (bSuccess)
        {
          m_pBitmapSubRegion = 
                           bsr.RetrieveBitmapOfSubRegion();
        }
      }
    }
  }
}

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