Re: [Flightgear-devel] SimGear/FlightGear Portability Patches

[Alessandro M. <ale...@ho...>]

Il 21/03/2015 23:13, Scott ha scritto:
> Hi Core Developers,
> 
> I’ve built SimGear/FlightGear from source and encountered a few portability issues with MSVC.  Attached are some patches for your consideration.
> 
> [...]
> [SimGear] Portability: Implemented Known Folders for Windows

Hi Scott,
a forum member testing a nightly build has encountered a problem while
running FG under Windows XP [1] - I think it might be related to your
"Known Folders" patch.

Specifically, it seems you're using WINVER to check if FG is run under
Windows XP or under a later version. However, the WINVER preprocessor
definition can be used only to check the minimum Windows SDK target
version on the system FG is compiled on - not the Windows version
available at runtime. As the build server has a fairly recent version
of the SDK, SHGetKnownFolderPath gets linked to the executable every
time; Windows XP correctly detects that the function is not available
on that OS and refuses to launch fgfs.exe.

You should detect the Windows version using the Version Helper API [2]
API and call SHGetKnownFolderPath dynamically (so that it is not
present in the linker table) [3].

Here's a sketch of the proposed solution (apologies for not sending
a fully working patch, I'm still trying to compile FG on my system):
-----
// Note: I assume the FG builders have the latest (8.1) Windows SDK
// installed. I use versionhelpers.h because GetVersion has been marked
// deprecated in Windows 8.1 and later, see [2].
#include <versionhelpers.h>
typedef void (STDAPI *PSHGKFP)(REFKNOWNFOLDERID, DWORD, HANDLE, PWSTR*);

static SGPath pathForKnownFolder(REFKNOWNFOLDERID folderId, const SGPath& def)
{
    PSHGKFP pSHGetKnownFolderPath;
    // system call will allocate dynamic memory... which we must release when done
    wchar_t* localFolder = 0;

    // Note: I suppose FG is already linked to shell32.dll. If it is not, a call to
    // LoadLibrary() should be made before this one.
    pSHGetKnownFolderPath = (PSHGKFP) GetProcAddress(GetModuleHandle(TEXT("shell32.dll")), "SHGetKnownFolderPath");
    if (NULL != pSHGetKnownFolderPath) {
        if (pSHGetKnownFolderPath(folderId, KF_FLAG_DEFAULT_PATH, NULL, &localFolder) == S_OK) {
            // copy into local memory
            char path[MAX_PATH];
            size_t len;
            if (wcstombs_s(&len, path, localFolder, MAX_PATH) != S_OK) {
                path[0] = '\0';
                SG_LOG(SG_GENERAL, SG_WARN, "WCS to MBS failed");
            }

            SGPath folder_path = SGPath(path, def.getPermissionChecker());

            // release dynamic memory
            CoTaskMemFree(static_cast<void*>(localFolder));

            return folder_path;
        }
    }
    // If the call to SHGetKnownFolderPath was unsuccesful or the function
    // was not found (even though we were on Windows Vista or later), return
    // the default path.
    return def;
}

// Then replace the WINVER detection with:
#ifdef _WIN32
    if (IsWindowsVistaOrGreater()) {
        case DESKTOP:
            return pathForKnownFolder(FOLDERID_Desktop, def);
        [...]
    } else {
        case DESKTOP:
            return pathForCSIDL(CSIDL_DESKTOPDIRECTORY, def);
        [...]
    }
#endif
-----

An alternative might be unifying the pathForKnownFolder and pathForCSIDL
functions and performing the Windows version check in there
(SHGetKnownFolderPath should still be called dynamically, though).

Cheers,
Alessandro Menti

[1] http://forum.flightgear.org/viewtopic.php?f=11&t=25831
[2] https://msdn.microsoft.com/en-us/library/windows/desktop/dn424972%28v=vs.85%29.aspx
[3] https://msdn.microsoft.com/en-us/library/windows/desktop/ms686944%28v=vs.85%29.aspx