Saying "P3D V4 SDK" can be a vague concept. There are many parts of it, and they affect the end result in very different ways.
There's an SDK for executable files, and there's a big difference between DLL/GAU files, which are running in the same process of the sim itself, and .EXE files, which run in another process, even when started by the sim.
- GAU/DLL files MUST be recompiled with the V4 SDK, which is 64 bit only. There are no shortcuts here, but there's also no risk the sim would have problems, because it will simply not load a 32 bit GAU/DLL in V4. In this case, our only .DLL module, the Addon Manager, it's obviously compiled with the V4 SDK, since it wouldn't even start otherwise.
- EXE files do not need to be recompiled, because they can still connect using Simconnect, which is a client-server system, not related to 32/64 bit issues. In our case, this is Couatl.exe, which is still a 32 bit application, but it also has a support .DLL which is compiled with the P3D SDK, in order to make some P3D-specific calls.
There's an SDK for scenery and models in general, which CAN be used, but the sim still supports models compiled using the FSX and even the FS9 SDK just fine. But using the native P3D SDK, allows scenery developers to simplify some things when layering ground polygons, and allows to compile objects with more polygons (there was a limit of 64K triangles per material in the FSX SDK). This is generally the same starting from P3D2, with some additions in V3 and even more in V4, with the most prominent being the dynamic lighting, which we use in KCLT. In KMEM we started using the native P3D SDK for the ground polygons. But, again, a scenery made for FSX will work just fine, except it won't use the new features.
Finally, there are SDK *guidelines* to INSTALL an add-on, which suggests that no add-on should install anything in the root of the sim, shouldn't modify the centralized scenery.cfg, prepar3d.cfg or DLL/EXE.XML files and should use Prepar3d.exe to add/remove such addon, at install time, since the sim itself has the ability to reconfigure its files, without 3rd party installers having to modify them directly, which is safer.
By following the P3D SDK installation guidelines, it's less likely add-ons will conflict with each other, or a faulty installer would screw up the sim main configuration files and, in case a reinstall of the sim would be required, add-ons following such guide lines can be re-enabled without having to reinstall them.
ALL our installers are following the Installation guidelines from the SDK.
