Not sure which forum this belongs in but here goes: Does anyone know a way to make a PD4 airport work in FSX?

Halwatk

PD4?  P3D version 4??  What airport?

If the scenery was really made for P3D4, it would be very difficult to convert it in FSX and, if the scenery is really a "proper" P3D4 scenery, it would be basically impossible, for the following reasons:

- Materials use different properties, especially the PBR one. This means all materials would have to be converted and all textures as well.

- Due to the usage of 16 bit numbers for polygons and vertexes in the FSX .MDL specifications, FSX has an hard limit of maximum 64K triangles per Draw Call, which forced developers to artificially break up objects to be under this limit, losing performances in the process, to create more complex objects. P3D uses 32 bit, so the limit is now way higher so, every object that has more than 64 triangles per draw call would have to be broken apart. It's already quite some work for the original scenery developer that has access to the sources, but it's almost impossible from a binary.

- Ground polygons in FSX had to use FS8 commands to allow multilayering in runways, markings, dirts, aprons. P3D has native commands to achieve the same, which makes the scenery being laid out in a totally different way. Even if you could convert it back to FS8 code, in addition to get MUCH lower performances, you'll still have to deal with the aforementioned 64K triangles per draw call limit, which would be particularly obvious with ground polygons.

- Some "proper" P3D4 sceneries might use advanced properties like the 2nd UV channel to have baked Ambient Occllusion or custom Details at a very low cost in fps. Replicating that in FSX would require creating entirely new polygon meshes to be alpha-blended on top of the base polygons, crippling the performances even more.

- If the scenery used skinned animation ( human characters, for example ), and reached the limit of 22 maximum Bones per Skeleton that exists in FSX ( compared to the 64/128 in P3D4 ), it would be almost impossible to convert that animation, so it would be best to just skip the object.

- If the scenery relied on realtime reflection, it would look very different in FSX that doesn't support them.

- FSX objects doesn't support objects casting shadows over themselves, so FSX sceneries usually try to fake them by baking shadows in their texture, but if the scenery was made for P3D and relied to that feature, its textures would look bland/flat in FSX.

 

There is a reason why scenery developers are moving away from FSX ( now there are even more reasons, since a new MSFS will come...), and it was to get rid of these limitations from 14 years ago, that's why it's so hard to convert a new scenery back to FSX. Provided is made as a proper P3D4 scenery, of course, and it's not just recompiled with the P3D4 SDK.

Thanks for that fascinating reply, it taught me a great many things that I did not know.