FSXA LOD problems

[Heretic]

Hey everyone,

I've recently tried to add some custom *Max created objects to a scenery. This worked quite well in the end, but since I'm a poly waster, having a few high-poly hangars around was kind of a huge performance killer.

So I tried to add LODs to the models. What showed up fine before now looks like this in FSX:


The hangar in question in FSX with its LODs as shown in the LOD tool:


I've used the naming convention for LODs from the FSX SDK.

Any ideas what could be causing this problem?

 

[arno]

Hi,

Since SP2 (and with Acceleration Pack as well), MS has added a feature that batches all polygons with the same material (even if within different objects). This increases the performance, but unfortunately during this change the LODs seem to have been broken. So I think it might be that you are hitting that problem.

 

[sruddy]

This advice from Farfy helped me with my LOD issues:

You don’t actually need to move the polygon, just give it the Part Name “Ambient” (for FSX) and set one key frame with out moving it, you get a warning that you have an empty animation, but it dosent seem to matter.
H_Farfy

http://www.fsdeveloper.com/forum/showthread.php?t=15010

 

[Heretic]

Thanks for the replies, guys. So it's all working via "empty animations", eh?

I don't quite understand that "ambient" thing though...do I have to rename every LOD model into e.g. "ambient_400", "ambient_150"?

I'm working with *real* LODs not "empty" ones.

 

[sruddy]

U just need a poly that is fake animated.
I had originally given up on lods as they just did not work.
Then Farfy mentioned the animation trick.
So I made a triangle that spun underground.
Farfy instructed me that it does not need to actually spin... the spinning try worked but is not necessary.

So no you do not need to make a bunch of lod ambient things. Just make your lods as you probably have but ad the one animated poly to your object.

 

[hcornea]

I have never had problems using LODs with FSX SP2 and Gmax - and I'm not sure why you would need to resort to a dummy animation (and the performance hit that might induce)

The problem in SP2 that LODding produces is that you are unable to LOD to a dummy - and must LOD to an actual renderable object (usually a 3 vertex single polygon)

Other than that LODs work fine.

All parts at a specific LOD level will be displayed and no others (so it works differently to FS9).

I was of the belief that the ambient tags were applied by the animation manager and that (unlike FS9) partname tags did not have an effect - but I must confess I haven't experimented in this area.

Looking at the pictures, the texture mapping seems scrambled on the canopy - is that what we are referring to here?

@Arno - you may have answered my question in the other thread about the effect of batching of Drawcalls.

 

[Heretic]

U just need a poly that is fake animated.
I had originally given up on lods as they just did not work.
Then Farfy mentioned the animation trick.
So I made a triangle that spun underground.
Farfy instructed me that it does not need to actually spin... the spinning try worked but is not necessary.

So no you do not need to make a bunch of lod ambient things. Just make your lods as you probably have but ad the one animated poly to your object.

Okay, so an extra, "emptily" animated triangle. Thanks.

Looking at the pictures, the texture mapping seems scrambled on the canopy - is that what we are referring to here?

As I said: The model looked fine in-sim before having added the LODs.

 

[decapod]

Another thread on a similar subject from last October you may like to read through...

http://www.fsdeveloper.com/forum/showthread.php?t=11751

 

[hcornea]

perhaps just to reiterate.

LODs DO work in FSX SP2 - that is the only platform we develop for, and some of the specific techniques require LODding to work properly.

You cannot LOD to a dummy object as you used to be able in FS9. You must lod to renderable object (single polygon - which can be below ground if desired)

Each LOD must be a complete representation of the object you want at that LOD level -- cumulative LODs as previously implemented in some FS versions do not work.

I have never seen texture scrambling with LODs -but I have not (to memory) made a hanger with quite as many vertices as that ..

@Bjorn - how did you make the LODs? (the screengrab shows only the LOD_400 version

What texture format are you using dds, any alpha?
Are you running FSX in DX10 preview mode?

Perhaps experiment with a slightly less complex object to get LODs working

(may I suggest 3 primitive shapes of different colours so you can see the switch points)

Alternatively - perhaps post your file? Maybe a 3ds guru might be able to help.

 

[Heretic]

Another thread on a similar subject from last October you may like to read through...

http://www.fsdeveloper.com/forum/showthread.php?t=11751

I've already read it; wasn't much help though. :/

@Bjorn - how did you make the LODs? (the screengrab shows only the LOD_400 version

Vertex weld with incrementally bigger thresholds (depending on LOD model).

I know, not the most elegant way. I've only wanted to reduce polygons.

What texture format are you using dds, any alpha?

Yes, .dds, with Alpha.

Are you running FSX in DX10 preview mode?

I'm on XP, so that's a clear "no".

Perhaps experiment with a slightly less complex object to get LODs working

(may I suggest 3 primitive shapes of different colours so you can see the switch points)

Good idea, might just try that.

Alternatively - perhaps post your file? Maybe a 3ds guru might be able to help.

Well, why not. Need to be back home first though since my laptop doesn't have my FSX development files on it.


Oh, and the reason I've used tons of polys is that I wanted things smooooooth.

 

[Heretic]

Okay, I'm back home and tried that "empty animation" thing. Worked in terms of getting FSX to switch LOD models and displaying the model correctly at highest LOD. See:



However, I've run into two problems:

- "Flashing" models (say appearing and disappearing). Happens during flight.
- Suboptimal looking LODs.



I have no idea what's causing problem #1, problem #2 could be caused by the way I've created the LODs (vertex weld).

Is there any efficient way to create LOD models, apart from welding vertices?


I've uploaded the .max file of the closed hangar here:
http://www.mediafire.com/download.php?htgfyz0iytf
(Texture included in .dds format, might need to be flipped.)

 

[arno]

Hi,

However, I've run into two problems:

- "Flashing" models (say appearing and disappearing). Happens during flight.
- Suboptimal looking LODs.

I have no idea what's causing problem #1, problem #2 could be caused by the way I've created the LODs (vertex weld).

Is there any efficient way to create LOD models, apart from welding vertices?

Problem one I have no clear idea. Is the whole object dissapearing or only part?

For the second problem. There are many ways to make LODs. Sometimes it might be even easier to start from scratch for the lower detail version and just make a simple shape. Sometimes combining vertices might work. The number of the LOD determines when it becomes visible, so by changing that you can also affect how the end result looks.

 

[Heretic]

Problem one I have no clear idea. Is the whole object dissapearing or only part?

The whole object.

For the second problem. There are many ways to make LODs. Sometimes it might be even easier to start from scratch for the lower detail version and just make a simple shape.

Starting over might be necessary. *Sigh*

The number of the LOD determines when it becomes visible, so by changing that you can also affect how the end result looks.

So I can put almost any number in there? How cool!

 

[sruddy]

Has anybody figured out what the LOD numbers correlate too? Something tangible like meters or is it just an index scale to itself?

 

[Heretic]

Has anybody figured out what the LOD numbers correlate too? Something tangible like meters or is it just an index scale to itself?

According to the SDK, the number indicates the threshold (in pixels) at which the object will switch to the next/previous LOD model.

Say a value of 400 would make an object switch LODs as soon as it's larger/smaller than 400 pixels on the screen.

 

[sruddy]

Thanks Heretic,
I missed that in my reading.

 

[hcornea]

The LOD switch will depend on a number of factors when the scenery is used ... the endpoint being the size in pixels, for the given aspect that would be rendered (or at least a box that represents that shape)

The problem with vertex weldig for textured objects is that it is likely to scramble your UVW mapping, and require re-mapping.

Depending on the shape ... you may plan to:

Start with your complex shape and simplify it (sy by removing higher poly parts and the like,or replacing curved objects with lowepoly equivalents.

Alternatively, you may start with a low-detail object, and add vertices/polygons as you go.

In the case of a curved canopy (example above) you might map it, then use a tesselate modifier, with a wave or other modifier - with different settings to make two or more versions of the shape.

If the object is disappearing, it is likely that there is a separate part that has its own LOD level.

At any LOD level, all and only the parts with that LOD suffix will be displayed. So if a small part has been cloned and has an errant LOD number - this will cause the object to disappear, when the sim decides to render that LOD. This is different to previous (FS9) LODs which added cumulative parts. In FSX you need complete alternative representations at each LOD level.

Check the parts listing to make sure that each LOD level includes the bits you want to render, and tha there are no extra LOD numbers with small parts in there.

 

[Heretic]

Alright. Back with new, simpler models (the hangars for example have just about one tenth of their original number of polygons), but with somehow related problems.



As you can see, the grass texture is still not displayed properly. How come? Wrong UVW mapping method?
I've used "face mapping"...


- Edit: Never mind, a "ZTest Alpha" with "0" and "Greater" fixed the drawing order issue on the light poles and the grass walls look better after I've set "plane" as the UVW mapping method.

 

[Heretic]

The hangar grass *still* looks wrong. But why?

 

[arno]

Hi,

It's hard to see on the screenshot, but two things come to my mind.

• Do you have volume shading enabled for the materials? If so check if you part is manifold (means closed, no gaps and holes).
• It could also be that you have duplicate polygons blending through each other