P3D v4 /xanim for LODs

[tsgucci]

Hi Arno!

I was converting some gltf objects with LOD into P3D objects (I merged the separate gltf LODs with the merge tool in MCX into a single a object). In MCX everything looked fine but in P3D the LOD never switched to the smaller LOD.
I did some experiment created a model with LODs without MCX (standard .x to mdl then to BGL) and still P3D did not switched the LODs. I thought the LOD system is somehow broken in P3D so I contacted them on their official forum. It turned out LOD switch only happens if the model has animation hence exported with .xanim and compiled with /xanim tag.

LOD switch is disabled? - Prepar3D Forums

www.prepar3d.com

I could not find any option in MCX to force xanim export and compilation. Could you please have a look in the logic?
Thanks a lot!

 

[arno]

Hi,

Yes, that has been the case since FSX already. MCX uses the /xanim flag when you export a MDL file. Only when you have drawcall batching enabled and the DrawcallBatchingWorkingLOD setting set to false it will not use that flag (to get drawcall batching on the cost of no LODs).

 

[tsgucci]

Hi,

Yes, that has been the case since FSX already. MCX uses the /xanim flag when you export a MDL file. Only when you have drawcall batching enabled and the DrawcallBatchingWorkingLOD setting set to false it will not use that flag (to get drawcall batching on the cost of no LODs).

THanks Arno!
Drawcallbatching is still a thing in P3D?

 

[arno]

Yes, that still works in P3D as well.

 

[tsgucci]

Hi Arno!

Maybe I am overcomplicating a littlebit.
So if I understand well a functional drawcall batching will only work if LODs are not and vica-versa.

If I understand well the settings if batching and batching LOD is both set to true then LOD will work if the object has LOD, if the object has no LOD then drawcall batching will work.
Interestingly I had True-True setting and LOD did not work anyway.

 

[arno]

Hi,

Correct, drawcall batching and levels of details don't work together, so you have to choose one of the two.

With the default true true setting you will get levels of detail when they are present and drawcall batching otherwise.

 

[tsgucci]

Hi Arno!

Of course it turned out that I was wrong again and MCX were working properly. The LOD switch happened just it happened from much farer distance. And this is due to the LOD calculation difference between P3D and MSFS.
In P3D the LOD number represents pixels, in case of MSFS it represents percentage of pixels on display. In MCX manual the MSFS method is not discussed.
It means if we convert MSFS models to P3D (or vica-versa) we need to recalculate the LOD values to have similar behaviour of the objects.

e.g.
If the P3D LOD is 400, it means for MSFS we need to give 400 / 1920 = 20 (%).
Other way round. If MSFS LOD is 80 then P3D LOD should be 1920 * (80/100) = 1536 (pixel)
If we consider screen size 1920 pixels.

I hope my logic is right.

 

[arno]

Hi,

MCX does attempt to convert between the values already. But it uses the screen resolution from the settings for that.

In the MSFS model xml there is a mimumum size specified, I'm not sure it's a percentage though.

 

[tsgucci]

Hi Arno

SDK says:

The new LOD rules will be as follows, based in part on the minSize parameter of the <LOD /> element in the Model Definitions file (the "minSize" is minimum size on screen - as a percentage - before a LOD model is considered for display):

SDK Documentation

docs.flightsimulator.com

 

[arno]

Let me double check my conversion then. It was implemented based on information from a asobo developer when the SDK was still almost empty

 

[tsgucci]

Let me double check my conversion then. It was implemented based on information from a asobo developer when the SDK was still almost empty

I know... The LOD documentation part and behaviour they changed already 2 times since the release.

 

[arno]

I have checked the implementation, but it is OK already. It converts indeed from a number of pixels on screen (FSX/P3D) to a size as a percentage between 0 and 100.

In MCX itself you will always see the FSX/P3D value. When exporting to glTF MCX will convert the LOD values when it writes the model XML file. On importing from glTF the inverse conversion is done.