title: Gdiplus Bitmap has no Alpha Channel
body: <p>I am trying to create a Gdiplus::Bitmap by a BITMAPINFO (shortened code example):</p>
  
  <pre><code>    BITMAPINFO bmi;
      HDC hdc;
      void* pvBits;
  
      ZeroMemory(&amp;bmi, sizeof(BITMAPINFO));
      bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
      bmi.bmiHeader.biWidth = some_width;
      bmi.bmiHeader.biHeight = some_height;
      bmi.bmiHeader.biPlanes = 1;
      bmi.bmiHeader.biBitCount = 24;
      bmi.bmiHeader.biCompression = BI_RGB;
      bmi.bmiHeader.biSizeImage = ((((bmi.bmiHeader.biWidth * bmi.bmiHeader.biBitCount) + 31) &amp; ~31) &gt;&gt; 3) * bmi.bmiHeader.biHeight;
  
      HBITMAP hBM = CreateDIBSection(hDC, &amp;bmi, DIB_RGB_COLORS, &amp;pvBits, NULL, 0x0);
      FillMemory(pvBits, bmi.bmiHeader.biSizeImage, 255);
  
      HGDIOBJ oldObj = SelectObject(hDC, hBM);
      ReleaseDC(NULL, hDC);
  
      GdiFlush();
  
      GdiPlusBitmap* bitmap = new Gdiplus::Bitmap(&amp;bmi, pvBits);
  </code></pre>
  
  <p>My Problem is that the created Bitmap has no alpha channel (PixelFormat24bppRGB). What am I missing?</p>