Loading JPG & PNG resources using GDI+

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<ul class=download>
<li><a href="cgdiplusbitmap/cgdiplusbitmap_demo.zip">Download demo project - 122 Kb </a></li>
<li><a href="cgdiplusbitmap/cgdiplusbitmap_src.zip">Download source - 1 Kb</a></li>
</ul>

<h2>Introduction</h2>

<p>Recently, I needed to display some JPG and PNG files. I had an old
copy of LeadTools and the open source libraries for both formats, but wanted my executable
to be as small as possible. So I decided to give GDI+ a try. I quickly found that
I'm not a big fan of GDI+--I find it poorly designed and very quirky--but it worked
well for my purposes until I discovered, to my horror, that GDI+ cannot load JPG or
PNG files stored as resources!</p>

<p>Like, I'm sure, other developers facing this issue, I disbelieved the
documentation and tried <code>Bitmap::FromResource</code> to no avail. While perusing the
Bitmap methods available, I ran across <code>Bitmap::FromStream</code>.</p>

<p>After a bit of testing and several errors, due mostly to the horrible GDI+
documentation, I came up with working code. After a night of rest, I decided
to encapsulate the code in a simple class to ensure memory got freed. The result
were two classes: <code> CGdiPlusBitmap</code> and <code>CGdiPlusBitmapResource</code>.</p>

<h2>The Gotcha</h2>

<p>Before discussing the code itself, there is a caveat with GDI+ that must be addressed.
In GDI+, the original image information must be available at all times--it does not double
buffer the data. In other words, if you open a bitmap using <code>Bitmap::FromFile</code>,
you cannot delete or otherwise change that file while the image is open. This same
restriction applies to the <code>CGdiPlusBitmapResource</code>.</p>

<p>In my second iteration of the code, I was creating the Bitmap using <code>Bitmap::FromStream</code>
and then freeing the global memory. Everything appeared fine until I attempted to draw
the bitmap, whereupon I got an generic error. Remembering the caveat about <code>Bitmap::FromFile</code>
I realized I needed to retain the allocated global memory, thus the desire for a class
that automatically frees that memory.</p>

<h2>The Class</h2>

<p>For kicks, I created two classes, with the base class being a very simple encapsulation
of Bitmap. I suppose that if I ever had the patience and desire, I could extend that class.
(Some may be curious why I didn't simply subclass the ATL class <code>CImage</code>. It's because the
<code>CGdiPlusBitmapResource</code> has to be used in code that doesn't use MFC or ATL. However, the code
is so simple, it could easily be modified to use <code> CImage</code> as the base class.)</p>

<p>I'm not even going to bother going over the <code> CGdiPlusBitmap</code> class except to say that it
has a single, public, data member <code>Bitmap* m_pBitmap</code>. (In the class I prefaced
the GDI+ objects with the <code> Gdiplus</code> namespace in case the developer doesn't want to declare
<code>using namespace Gdiplus;</code>.)</p>

<p>The <code> CGdiPlusBitmapResource</code> class has several constructors and several overloaded
<code>Load</code> functions. The overloaded functions simply allow lazy programmers,
like myself, to not have to type <code>MAKEINTRESOURCE</code>. The main <code>Load</code>
function takes the resource name and type as strings and is the key to the class. This
code follows in its entirety:</p>

<pre>
inline
bool CGdiPlusBitmapResource::Load(LPCTSTR pName, LPCTSTR pType, HMODULE hInst)
{
    Empty();

    HRSRC hResource = ::FindResource(hInst, pName, pType);
    if (!hResource)
        return false;
    
    DWORD imageSize = ::SizeofResource(hInst, hResource);
    if (!imageSize)
        return false;

    const void* pResourceData = ::LockResource(::LoadResource(hInst, hResource));
    if (!pResourceData)
        return false;

    m_hBuffer  = ::GlobalAlloc(GMEM_MOVEABLE, imageSize);
    if (!m_hBuffer)
        return false;

    void* pBuffer = ::GlobalLock(m_hBuffer);
    if (!pBuffer)
    {
        ::GlobalFree(m_hBuffer);
        m_hBuffer = NULL;
        return false;
    }

    CopyMemory(pBuffer, pResourceData, imageSize);

    IStream* pStream = NULL;
    if (::CreateStreamOnHGlobal(m_hBuffer, TRUE, &amp;pStream) == S_OK)
    {
        m_pBitmap = Gdiplus::Bitmap::FromStream(pStream);
	    pStream-&gt;Release();
    }

    return m_pBitmap &amp;&amp; m_pBitmap-&gt;GetLastStatus() == Gdiplus::Ok;
}</pre>

<p>I find the code very self explanatory, though those that know the return
value of <code>::LoadResource</code> is an <code> HGLOBAL</code> may find the apparent
double copy using <code>CopyMemory</code> confusing. In brief
<code>CreateStreamOnHGlobal</code> requires a <code> HGLOBAL</code> handle
allocated by <code> GlobalAlloc</code> using the <code> GMEM_MOVEABLE</code> flag.</p>

<h2>The Demo</h2>

<p>The demo was thrown together with Visual Studio .NET 2002 (VC++ 7.0) and
was tested under Windows XP. If you want to compile it with VC++ 6.0, you
can convert the project using a utility here on CodeProject.</p>

<p>The demo allows you to load resampled JPG or PNG files (For the curious I
took both photographs in Oahu, Hawaii for, and while filming content of, a
multimedia product. One is of Laie Bay, the other is a sunset viewed from Waikiki.)</p>

<h2>Disclaimer</h2>

<p>I am not a GDI+ expert, nor am I a big fan. Please don't ask me questions
about it, though if you have any suggestions or improvements, please let me know.</p>





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