From f151a5d11db0330cbbc7fbde3b4b76c328357b25 Mon Sep 17 00:00:00 2001
From: bzt <bztemail@gmail.com>
Date: Fri, 13 Dec 2019 09:04:40 +0100
Subject: [PATCH] MSVC2013 alternative to thread_local

---
 code/M3D/M3DWrapper.cpp | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/code/M3D/M3DWrapper.cpp b/code/M3D/M3DWrapper.cpp
index 46f3278cb..c0de1cf31 100644
--- a/code/M3D/M3DWrapper.cpp
+++ b/code/M3D/M3DWrapper.cpp
@@ -48,10 +48,20 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <assimp/IOStreamBuffer.h>
 #include <assimp/ai_assert.h>
 
-// workaround: the M3D SDK expects a C callback, but we want to use Assimp::IOSystem to implement that
+#if (__cplusplus >= 201103L) || !defined(_MSC_VER) || (_MSC_VER >= 1900) // C++11 and MSVC 2015 onwards
+# define threadlocal thread_local
+#else
+# if defined(_MSC_VER) && (_MSC_VER >= 1800) // there's an alternative for MSVC 2013
+#  define threadlocal __declspec(thread)
+# else
+#  define threadlocal
+# endif
+#endif
 
 extern "C" {
-thread_local void *m3dimporter_pIOHandler;
+
+// workaround: the M3D SDK expects a C callback, but we want to use Assimp::IOSystem to implement that
+threadlocal void *m3dimporter_pIOHandler;
 
 unsigned char *m3dimporter_readfile(char *fn, unsigned int *size) {
 	ai_assert(nullptr != fn);