Support using open-sourced DirectX headers.
diff --git a/include/D3D12MemAlloc.h b/include/D3D12MemAlloc.h
index 7ebcf98..6b11a99 100644
--- a/include/D3D12MemAlloc.h
+++ b/include/D3D12MemAlloc.h
@@ -61,7 +61,13 @@
 // If using this library on a platform different than Windows PC or want to use different version of DXGI,

 // you should include D3D12-compatible headers before this library on your own and define this macro.

 #ifndef D3D12MA_D3D12_HEADERS_ALREADY_INCLUDED

-    #include <d3d12.h>

+    #if defined(USING_DIRECTX_HEADERS)

+        #include <directx/d3d12.h>

+        #include <dxguids/dxguids.h>

+    #else

+        #include <d3d12.h>

+    #endif

+    

     #include <dxgi1_4.h>

 #endif