<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<!-- saved from url=(0103)http://www.codeproject.com/script/Submit/ViewHTML.asp?guid=cgdiplusbitmap%2Fvcpp%2Fgdiplus1%2F21%2F2003 -->
<!-- HTML for article "Loading JPG & PNG resources using GDI+" by Joe Woodbury,Joe Woodbury
URL: http://www.codeproject.com/vcpp/gdiplus/cgdiplusbitmap.asp
Article content copyright Joe Woodbury,Joe Woodbury
All formatting, additions and alterations Copyright � CodeProject, 1999-2004
--> <!----------------------------- Ignore -----------------------------><HTML><HEAD>
<META http-equiv="Content-Type" content="text/html; charset=windows-1252">
<LINK href="CGdiPlusBitmapTest_files/global.css" type="text/css" rel="stylesheet">
<META content="MSHTML 6.00.2800.1400" name="GENERATOR"></HEAD>
<BODY>
<P><B>Please choose 'View Source' in your browser to view the HTML, or File | Save to
save this file to your hard drive for editing.</B></P>
<HR noShade SIZE="1">
<!----------------------------- Ignore -----------------------------> <!----------------------------- Article Starts ----------------------------->
<UL class="download">
<LI>
<A href="http://www.codeproject.com/vcpp/gdiplus/cgdiplusbitmap/cgdiplusbitmap_demo.zip">
Download demo project - 122 Kb</A>
<LI>
<A href="http://www.codeproject.com/vcpp/gdiplus/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 GDI+ to be 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 images 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. With JPG, some TIFF and other formats, the original image
information must be available at all times. 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 <CODE>CGdiPlusBitmapResource</CODE>.
(My testing found that PNG and BMP files don't seem to follow this
generalization, though I don't know if this is standard behavior or just a
fluke with my file set.)</P>
<H2>GDI+ Initialization</H2>
<P>GDI+ needs to be initialized before any GDI+ calls are made. I suggest adding
the following data member to the class derived from <CODE>CWinApp</CODE>:</P>
<PRE>ULONG_PTR m_gdiplusToken;</PRE>
<P>In <CODE>InitInstance()</CODE>, add the following calls:</P>
<PRE>Gdiplus::GdiplusStartupInput gdiplusStartupInput;
Gdiplus::GdiplusStartup(&m_gdiplusToken, &gdiplusStartupInput, NULL);</PRE>
<P>In <CODE>ExitInstance()</CODE>, add the following:</P>
<PRE>Gdiplus::GdiplusShutdown(m_gdiplusToken);</PRE>
<H2>The Class</H2>
<P>I created two classes, with the base class being a very simple encapsulation of
<CODE>Bitmap</CODE> and the derived class encapsulating the global memory. I
suppose that if I ever had the patience and desire, I could extend that class,
but I have no need to do so. (If you're curious why I didn't simply derive from
the ATL class <CODE>CImage</CODE>, it's because the code was used in a
program that didn'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 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)
{
void* pBuffer = ::GlobalLock(m_hBuffer);
if (pBuffer)
{
CopyMemory(pBuffer, pResourceData, imageSize);
IStream* pStream = NULL;
if (::CreateStreamOnHGlobal(m_hBuffer, FALSE, &pStream) == S_OK)
{
m_pBitmap = Gdiplus::Bitmap::FromStream(pStream);
pStream->Release();
if (m_pBitmap)
{
if (m_pBitmap->GetLastStatus() == Gdiplus::Ok)
return true;
delete m_pBitmap;
m_pBitmap = NULL;
}
}
m_pBitmap = NULL;
::GlobalUnlock(m_hBuffer);
}
::GlobalFree(m_hBuffer);
m_hBuffer = NULL;
}
return false;
}</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 is a Visual Studio .NET 2003 project with ANSI and UNICODE builds. It
allows you to load resampled JPG or PNG resources (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>GDI+ Disclaimer</H2>
<P>I am not a GDI+ expert, nor am I a big fan, even if I do find GDI+ occasionally
very useful. Please don't ask me questions about it.</P>
<H2>Why not IPicture?</H2>
<P>I've been asked why I didn't use <CODE>IPicture</CODE>. The answer is threefold;
first, <CODE>IPicture</CODE> does not support PNG images. Second, <CODE>IPicture</CODE>
is pretty much only an image loader, with little more capability than the
standard GDI bitmap calls. Third, <CODE>IPicture</CODE> decodes the image data
immediately. JPG and GIF images will use more memory than this class. </P>
<H2>Updates</H2>
<P>22 April 2004 <BLOCKQUOTE>
<P><CODE>CreateStreamOnHGlobal</CODE> now uses <CODE>FALSE</CODE> for the second
argument since <CODE>Bitmap</CODE> requires that the memory be retained for at least JPG
images and I decided to err on the side of caution. Interestingly, my testing
showed this flag is often ignored, but I received reports that this wasn't
always the case and <i>was</i> technically incorrect.</P>
<P>In addition, while fixing this bug I realized I wasn't clearing up the global
memory on failure. That resulted in the code being rearranged as it is now.</P>
</BLOCKQUOTE>
<P>15 June 2004 <BLOCKQUOTE>
<P>If <CODE>Gdiplus::Bitmap::FromStream</CODE> fails, I added what I believe is
redundant, but more correct code in handling <CODE>m_pBitmap</CODE>.
(Unfortunately, the documentation is silent on the subject as to whether NULL
will always be returned on failure.)</P>
</BLOCKQUOTE>
<P>3 September 2004 <BLOCKQUOTE>
<P>Added a section on GDI+ initialization.</P>
<P>Fixed a potential memory leak on image load failure in the sample application.</P>
</BLOCKQUOTE>
<!----------------------------- Article Ends -----------------------------></BODY></HTML>
Submit an article or tip