Function ExtractIconFromExecutable

source/util.cpp:2560–2658

L17: Extract icon of the appropriate size from an executable (or compatible) file.

// L17: Extract icon of the appropriate size from an executable (or compatible) file.
HICON ExtractIconFromExecutable(LPTSTR aFilespec, int aIconNumber, int aWidth, int aHeight, HMODULE *apModule)
{
	HICON hicon = NULL;

	// If the module is already loaded as an executable, LoadLibraryEx returns its handle.
	// Otherwise each call will receive its own handle to a data file mapping.
	HMODULE hdatafile = aFilespec ? LoadLibraryEx(aFilespec, NULL, LOAD_LIBRARY_AS_DATAFILE) : g_hInstance;
	if (hdatafile)
	{
		LPTSTR group_icon_id = (aIconNumber < 0)
			? MAKEINTRESOURCE(-aIconNumber)
			: ResourceIndexToId(hdatafile, (LPCTSTR)RT_GROUP_ICON, aIconNumber ? aIconNumber : 1);

		HRSRC hres;
		HGLOBAL hresdata;
		LPVOID presdata;

		// MSDN indicates resources are unloaded when the *process* exits, but also states
		// that the pointer returned by LockResource is valid until the *module* containing
		// the resource is unloaded. Testing seems to indicate that unloading a module indeed
		// unloads or invalidates any resources it contains.
		if (group_icon_id != RESOURCE_ID_NOT_FOUND
			&& (hres = FindResource(hdatafile, group_icon_id, RT_GROUP_ICON))
			&& (hresdata = LoadResource(hdatafile, hres))
			&& (presdata = LockResource(hresdata)))
		{
#pragma pack(push, 1) // For RESDIR, mainly.
			struct NEWHEADER {
				WORD Reserved;
				WORD ResType;
				WORD ResCount;
			};
			struct ICONRESDIR {
				BYTE Width;
				BYTE Height;
				BYTE ColorCount;
				BYTE reserved;
			};
			// Note that the definition of RESDIR at http://msdn.microsoft.com/en-us/library/ms648026 is
			// completely wrong as at 2015-01-10, but the correct definition is posted in the comments.
			struct RESDIR {
				ICONRESDIR Icon;
				WORD Planes;
				WORD BitCount;
				DWORD BytesInRes;
				WORD IconCursorId;
			};
#pragma pack(pop)

			if (aWidth == -1)
				aWidth = aHeight;
			if (aWidth == 0)
				aWidth = GetSystemMetrics(SM_CXICON);

			NEWHEADER *resHead = (NEWHEADER *)presdata;
			WORD resCount = resHead->ResCount;
			RESDIR *resDir = (RESDIR *)(resHead + 1), *chosen = NULL;
			int chosen_width = 0;