Category: File Formats

The Global Scenery Folder

Let me answer two questions right now:

  1. If you bought version 9 beta DVDs, you will not have to buy new ones when version 9 goes final.
  2. If you bought version 9 beta DVDs, you do not need to manually move around any of the global scenery files that our installers put on your hard drive.

Now about this global scenery folder…

X-Plane stores its scenery in packages – a scenery package is a folder that contains all of the files needed for a given scenery element, whether custom or default. In X-Plane 7, scenery packages were only used for custom scenery, and always lived in the Custom Scenery folder directly next to the X-Plane application. This provided an easy way for users to drag third party packages into a single location to install them. (Before the custom scenery folder, installing scenery could involve a lot of “put this file here, and that file there”.)

X-Plane 8 added a second location, the Default Scenery folder, which is hidden away inside the resources folder; it acts as a repository for scenery packs we ship with the sim, such as the one that contains various airport elements, and the default road packs.

In X-Plane 7 the global scenery lived directly in the resources folder in its own home; in X-Plane 8 the global scenery lives in packages inside the default scenery folder…this allows us to use one piece of code (the package loader) to load all scenery, custom and global.

The only real differences between the default scenery and custom scenery folders was priority and intended use; custom scenery is loaded with higher priority than default scenery (so you see your custom add-ons replace our default work), and the intention is that the default scenery is for Laminar to update via the web-updater and custom scenery is for you to put things into that you download off the web, etc.

With X-Plane 9 we are introducing a third location for scenery packages: the “Global Scenery” folder. It will live next to the Custom Scenery folder and X-plane application and be the location for global scenery. Its priority is intermediate – higher than default but lower than custom.

Now here’s the funky thing: the X-Plane 9 beta DVDs place the global scenery into the custom scenery folder. If you’ve ever looked at the ranking of scenery packages, you’ll see that they come out lower priority than all custom scenery, regardless of the alphabetical sorting that is usually used. The sim recognizes the peculiar placement of the global scenery and effectively labels it “global”.

Future DVD pressings will simply place the global scenery in the new global scenery folder. Thus we get to the original two answers:

  1. You won’t have to buy new DVDs if you have the betas; the sim will continue to work with either the beta or the newer layout for global scenery for the entire v9 run.
  2. Because both layouts work you don’t need to move anything around. I suggest you not move any files to lower the risk of breaking things.
Posted in File Formats, Scenery by | 3 Comments

X-Plane 9: What Comes Next

X-Plane 9.00 is going to be going final pretty soon – we’re on RCs right now. But this is hardly the end of the road; rather it’s the first step for a number of new development areas. What comes next?

Tools: I am working on tools releases now; a few users already have alpha copies of MeshTool. My hope is to have some new tools posted tomorrow, with more by the end of the week

More rendering engine/shader work: X-Plane 9 only begins some of the shader work we want to do; more engine enhancements will be coming in 910. Like 9.00, more advanced rendering will consume more hardware, and will be scalable via rendering settings.

Systems and Airplane SDK: X-Plane 9 introduced a lot of new features for airplane modeling, but there’s still more to do. I hope to have the panel region system and advanced lighting options all fleshed out for 9.10. Austin is doing a lot of work on systems modeling. We’ll be making more new airplane-related datarefs to tie it all together.

Orthophoto Scenery: I don’t know if this is going to happen or not, but we get more and more requests for large-orthophoto-scenery support in X-Plane; MeshTool is only going to increase that desire by making it possible to cover large areas with orthophotos without sacrificing framerate. So I would like to do some work on the texture pager, but I do not know if I’ll be able to do that in time for 9.1.

My hope is to get 9.1 into beta early so that we can start getting third party aircraft authors involved with trying new features. If you are working on an advanced airplane, keep in touch!

Posted in Aircraft, File Formats, Scenery by | 6 Comments

Don’t use ATTR_cockpit outside the cockpit objects

I’ve blogged about this before, but…let me be totally clear:

Don’t use ATTR_cockpit in objects that are not one of the two cockpit objects for your airplane.
Don’t use ATTR_cockpit in the attached misc. objects for your plane – move the parts of the mesh that require ATTR_cockpit into the cockpit object.
Don’t use ATTR_cockpit in scenery objects.
The OBJ spec basically says as much when it says “don’t use cockpit features” outside of cockpits.
Now what goes wrong if you violate this varies with the betas vs. X-Plane 8, but I can tell you this: no version of X-Plane has ever shipped that will correctly handle ATTR_cockpit in attached objects for all cases.  There’s always been bugs in this not-such-a-good-idea code path; it’s just the severity has varied over time.
Posted in Cockpits, File Formats, Modeling by | Comments Off on Don’t use ATTR_cockpit outside the cockpit objects

The Limits of Orthophotos and Meshes in X-Plane

I get asked a lot about the limits of meshes and orthophotos in X-Plane. I’ll try to answer this, but the answer isn’t as simple as most people expect.

Texture Limits and Orthophotos

The maximum single texture size in X-Plane 8 is 1024×1024, and in X-Plane 9 it is 2048×2048.

I believe the maximum number of unique custom orthophotos that can be attached to a single DSF is at least 32768.

In practice, that number is pretty useless because X-Plane loads all textures for a DSF at the highest user-allowed res when the DSF is loaded. That means you tend to load a lot of textures. Every system is different and drivers have a lot to do with RAM efficiency, but generally you’ll run out of virtual address space and crash the sim before you can attach 32768x2048x2048 of pixels.

X-Plane has no limits on how the texturing is applied – that is, you can use your 2028×2048 texture to cover an entire tile or a single meter. So again, the limiting factor on the resolution of your orthophotos is how much total area you want to cover and how much RAM you can spend (remember RAM is also used for mesh complexity, 3-d models, etc.).

You do not need to have enough VRAM to hold all loaded orthophotos; the video driver will paeg the textures into VRAM. Virtual address space is the limiting factor. How far you push it depends on a lot of subjective things:

  • If you expect your users to also run with a lot of trees, 3-d objects, cars on roads, and some plugins, you can’t use a lot of RAM.
  • If you expect your users to have /3GB in their boot.ini and use nothing but your add-on, you can use a lot more RAM.

Generally the size of the DDS texture on disk is a good proxy for the virtual memory that is required to hold your textures.

It should be noted that these limits on texturing (due to X-Plane blindly loading a lot of stuff at once) affect all scenery types: objects, draped polygons, very complex airplanes, plugins, and not just terrain mesh orthophotos.

Getting Past the Texture Limit

It will take a future extension to the rendering engine to get past the current limits. Basically X-Plane will have to load textures at lower resolutions when they’re farther away. I don’t know when that is coming, but when it happens, it will increase the total amount of image data a DSF mesh can contain, because the limiting factor will be how much data is in the small area the user is looking at (since the rest can be stored at much lower res for far-away views). At that point the limiting bottleneck will be resolution (smaller means more data at once), not total image data.

Mesh Limits

Unfortunately, limits to the mesh are even more vague than limits to texture usage. X-Plane uses an adaptive mesh – basically you can put your vertices wherever you want. So the highest resolution you can achieve might be much smaller than 1 meter resolution, but you can only do this for a small area before the total mesh size gets too big. But this is okay – the intention of DSF is to let you put a lot of detail where you need it.

I believe that once again memory provides the first limitation to the mesh. That is – you’ll run out of memory loading your insanely huge mesh long before you hit a limit to the DSF container structure. And once again, even the RAM limit isn’t a hard limit because that virtual address space is shared with texures. Your mesh density limits actually go down when your textures go up because it’s a zero-sum game.

Estimating Memory

Here are some ideas on how to estimate your memory footprint:

  • Run X-Plane over ocean to get an idea of the baseline memory use that the sim needs without extra scenery.
  • Load your mesh without textures (move the textures away) to find the cost of the mesh itself. (I am going on the assumption here that you can rescale your mesh using whatever mesh generation tool you’re using).
  • The size of DDS textures is a good proxy for the memory used.
Posted in File Formats, Scenery by | 2 Comments


I may be fighting a pointless and unwinnable linguistic battle, but I have to try. People very often refer to the default city buildings in X-Plane as “auto-gen” but by any reasonable definition of “auto-gen” they are not really auto-gen at all.

Now these are all made up computer terms, so we can’t really check the dictionary. But “autogen” scenery (short for automatically generated) usually refers to scenery that is created by a flight simulator itself, usually while you fly, and usually by placing 3-d detail in places that match the base terrain. This exists in FSX, and existed in X-Plane up to version 7.63.

X-Plane 8 doesn’t have autogen!!!!!!! X-Plane 8 has scenery that is generated by computer programs, but X-Plane is not the computer program that is doing it. When you see a ton of buildings piled up in New York City, that is not becaues X-Plane looked at the New York city base terrain and said “hrm – some buildings would be nice.”

What actually happens is we analyze New York City when we create the global scenery (before we ever burn the DVD masters) and the DSF generator places all of those buildings in New York City. X-Plane simply gets a huge list of buildings from the DSF and draws them.

I am going to try to coin the term “algogen” (algorithmically generated) to describe these buildings that (like autogen) come from a computer generating semi-random buildings from input data, but unlike autogen, algogen is a process that runs once before the scenery is made.

So how is algogen and autogen different?

  • You can’t change the pattern of algogen building placement by editing files in the sim. The algorithm has already been run! You can replace the buildings using an overlay (that excludes the base) or by using a library of models to substitute models.
  • We are trading data size for computation. The DSF is bigger because it lists the location of every building in New York, even if they were just algogen buildings, but the job of placing those buildings is less difficult because X-Plane does not have to check each building against each road. That has been done in advance.
  • Changing the scenery via an overlay doesn’t change the algogen! Add an airport via an add-on and you have to exclude the buildings. (But if you send that airport to Robin, the next global render will include it and the algogen will skip the airport automatically.)

Note one of the interesting results of algo-gen: X-Plane can’t tell the difference between an alg-gen building and a hand-placed one! They’re all just objects in a DSF. The fact that algo-gen buildings disappear with lower settings is because the sim/require_object property in the DSF header tells the sim which objects are important, and our generator always signals the buildings based on obstacle data as important. But algogen as a process is not visible to X-Plane!

And that’s why I’m spending so many words on trying to distinguish between “algogen” and “autogen” – because the processes are fundamentally different, they’re very different for scenery authors to work with. As a result, authors coming from X-Plane 7 or FSX will be very surprised if they try to understand X-Plane in terms of autogen….they won’t be able to find the autogen config files, and the autogen buildings won’t react to other scenery changes, because they’re not actually autogen at all!

Algogen is a classic pattern of “precompute” vs. “compute-while-fly”. Generally precomputing gives authors more flexibility (in our case, we have an obj engine that can handle a lot of objects, so authors can make their own objects of the same density as algo-gen with the objects placed anywhere) at the expense of making it more complex to edit the existing scenery (edit the mesh and the algogen doesn’t change).

When we started the v8 scenery, two things pushed me toward precomputation:

  • In the past, changes in X-Plane’s rendering engine had broken third party add-ons. So a precomputation strategy (by getting the scenery code out of the sim) means that the sim is doing less “interpretation” and thus the interpretation of scenery is less likely to change.
  • We wanted to focus on performance, which means getting computation out of the sim whenever we could.

Now that last point isn’t quite as important as it used to be…when we were doing the design (during mid X-Plane 7), dual core for everyone wasn’t on the radar, so the penalty for complex computation while flying is lower (and thus we have more expensive in-flight computation, like forests and completely draped bezier curve-based polygonal pavement).

But I think precomputation is still useful. Even with dual core, the algorithm that places X-Plane’s algo-gen bulidings can take one to two minutes for a 1×1 DSF tile on a very fast computer. That’s still a load time that’s out of the question for us; even on the second core, the DSF wouldn’t be “ready” in time for you to fly it. So one use of precomputation is to run algorithms that are more expensive than you can have in real-time. (That algorithm to pack objects inside an irregularly shaped polygon made by roads and land features is not fast.)

More importantly, precomputing does give us a nice advantage in the use of storage data. We ship about 50-60 GB of final scenery, but the source data is well over 100 GB. When we run the algogen algorithm, we have access to the full set of source data: coastlines, elevation, and land use before any simplification is done and any data is thrown out. So we have the potential not only to do a more complex analysis, but to do the analysis on a larger data set.

The down-side of precomputing is that if integration of all data is saved until sim time, there is the potential for third parties to contribute separate data to the sim via add-ons and still have the integration of those data sets work well. This doesn’t always work out – see complaints in online magazine reviews about combining orthophotos and new road grids in FS2K4…they don’t integrate because neither of those types of resources can be integrated to match the other in real time. But autogen still does a much better job than algogen at this; algogen basically has to be recut when other data changes. (And that is our intention – if you change the road grid, exclude and replace the objects too!)

Posted in Development, File Formats, Scenery by | 4 Comments

Airplanes – How it Fits Together

Here’s a summary of the new airplane features in 9.0 (and some coming). Hopefully this will give you an idea of what new capabilities are available for modeling planes in X-Plane 9. This list will sound like a broken record – virtually all of these features are optional; you don’t have to recut your finished airplanes to use them in version 9.

2-d vs. 3-d Panel

You may have noticed the new “3-d panel” option in PlaneMaker 9. This allows you to build a separate panel for the purpose of providing the texture to ATTR_cockpit (or ATTR_cockpit_region). You can then:

  • Provide alternate instrument artwork in a cockpit_3d folder. (This lets you have perspective artwork for the 2-d cockpit and orthogonal artwork for the 3-d cockpit.)
  • Pack your instruments together tightly to save space. (There is a real cost to large panels, so using a 1024×1024 panel for the cockpit object is a lot better.)

The 3-d panel is strictly optional, fully replaces the 2-d panel only for cockpit objects, and is activated by providing a custom panel background in a cockpit_3d folder. (See the “Example Plane-Widescreen+objects” plane in beta 19.)


Cockpit regions are an alternative to using the entire 2-d panel to texture your objects. They provide a few advantages:

  • Performance. By requiring a power of 2 and allowing you to use a sub-area of the panel, cockpit regions avoid a lot of wasted computing that ATTR_cockpit can cause.
  • Next-gen lighting. Unlike ATTR_cockpit, real 3-d lighting is applied to the panel when you use this attribute. This means that you will get a gradual decrease in light on your geometry (correct based on the angle of the sun) that matches the rest of the object.

Please note that you can mix and match which way you get your cockpit texture and whether you use the 2-d or 3-d panel feature (above) independently. However, you can only use ATTR_cockit or ATTR_cockpit_region in your airplane, not boht. ATTR_cockpit is still supported.

Generic Instruments

Generic instruments let you build instruments that follow some basic shapes (needles, tapes, etc.) that can be tied to any dataref. This both lets you customize particular instruments very precisely or create an instrument driven by a plugin dataref. These instruments are optional in version 9 – the old “premade” instruments are still supported.

New Datarefs

X-Plane 9 provides new datarefs targeted at airplane authors. The datarefs are better organized and have clearer names. But the old datarefs still exist, so legacy planes do not have to be updated.

Generally the entire cockpit should use only sim/cockpit2/ datarefs, and the plane exterior should use only sim/flightmodel2/ datarefs.

One special feature of these two sections: if your plane is used as an AI plane, these datarefs will animate the plane with the AI plane’s control deflections, not the user’s control deflections. So using these datarefs fixes the “AI animation” problem.

Plugins in Aircraft Folder

Version 9 airplanes may have a plugins folder (inside the ACF package) with fat plugins inside them. If you develop a plugin for your airplane, consider packaging it this way — this will allow your users to install the airplane with a single unzip for all platforms and no extra “drag-this-file-here”.

Plugins in the airplane folder is optional – you don’t have to provide a plugin, and plugins that are installed in the main Resources/plugins folder will still work. Still, I encourage you to use this feature because it makes the install process a lot simpler. The X-Plane SDK website will have documentation on fat plugins.

Liveries Folder

X-Plane 9 features a new “liveries” folder. Liveries (replacement exterior paint for airplanes and their attached objects) can be placed in packages in the liveries folder to greatly simplify the process of repainting an aircraft. See the “Example Plane-Widescreen+Objects” for an example.

While the liveries feature is optional, I strongly encourage anyone doing repaints to adopt it. Liveries can be switched by the user in the sim without any file manipulation; there is thus no risk of accidentally deleting or breaking an aircraft.

Large 2-d Panels

In X-Plane 9, a panel can be up to 2048×2048 in size. You pick the dimensions. The panel will scroll horizontally if necessary.

Note that if you use the new 3-d panel feature, the 2-d and 3-d panel do not have to be the same size. I would recommend a large 2-d panel (to fill large monitors) and a smaller 1024×1024 3-d panel (for performance).

Hiding Parts

X-Plane 9 will allow you to hide aircraft parts. Many v8 planes use OBJs to model the plane geometry, and use a transparent ACF texture to hide the ACF. Setting the parts to “not drawn” saves the CPU time that X-Plane would spend drawing the airplane, and is thus more efficient.


X-Plane 9 supports key-framed animation; this is useful for the scenery system, but for airplanes it allows for much more complex and realistic animation. OBJs that don’t have key frames still work.


This is a feature coming in the future: the ability to control how the user clicks and interacts with the cockpit object in detail. In X-Plane 9.0 we only support clicking on cockpit-textured geometry; manipulators will make features like draggable handles a lot more workable.

Global Illumination

X-Plane 9 does not yet offer a lot of control of the in-cockpit lighting environment; we’ll be working on this in future versions. These features will be opt-in…that is, you’ll have to change your model to get the new features, and old planes will work the way they always used to. It is likely that you’ll have to use “modern” airplane-building techniques to use these new features (meaning OBJs, named or custom lights, lego brick instruments ,etc.).

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When Can You Not Use DDS?

There are a few cases where you cannot use DDS files in X-Plane:

  1. Airplane 2-d panels (any layer – base, lit, -1 shadow layer, 2-d or 3-d).
  2. Airplane instrument images.
  3. Bitmap-based region specification referenced in a library.txt file.
  4. Any gray-scale/alpha-only texture (e.g. mask files in the scenery system).

Beta 17 is treating cases 1 & 2 as an error; beta 18 will simply stop looking for DDS files in those cases.

Please note that airplane panels and instruments are not compressed right now, so there would be no performance benefit to using DDS in these cases. (If anything, PNG has smaller file size when compression is not used.) If we ever allow compressed panel textures, we’ll probably allow DDS panels at the same time.

Case 3 is just a particular version of case 4 – that is, the region bitmap is black and white (1 channel) so DDS provides no benefit. Use a gray-scale no-alpha PNG!

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Panels Will Be Opt-In

First, the most salient point: in X-Plane 9.00 beta 16, 2-d panels and 3-d cockpits should both look the way they did in version 8. That is, your v8 plane should look good in v9 without modification. This is due to both:

  • A bunch of bug fixes regarding burn-in and night lit layers.
  • “3-d” lighting is not applied to the cockpit texture.

On this last point, my hope had originally been that I could apply 3-d lighting to the cockpit and simply make existing content look better. It has become painfully clear to me that this is not possible — existing planes are very carefully tuned to look good despite what I can only describe as “inconsistent” lighting rules in v8. Applying more consistent general 3-d lighting wrecks this tuning.

So new features regarding 3-d cockpits will be opt-in – that is, you will have to change your model to start using them. Existing content will work the way it used to.

I will explain what new features are available in 9.0 and what will come in 9.1 in a separate post real soon.

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Scenery and the New Plugin SDK

Sandy and I are working on a major revision to the plugin SDK (all the old stuff will work, we’re just adding new things) that should be available in X-Plane 9 soon. The new “2.0” SDK APIs include some new functionality for working on scenery.

  • Plugins can find the height of the ground at a given location, which is necessary to draw in the 3-d world in a realistic way (e.g. vehicles that drive on the ground in a sloped airport environment).
  • Plugins can load and draw OBJ files using X-Plane’s built-in facilities. I’ve posted OBJ drawing code in the past, but this makes things even easier.
  • Plugins can lookup virtual paths in the library to find artwork from scenery packages.

This makes a number of scenery-system concepts available to plugins.

I’ve been resisting OBJ-drawing support in the SDK for a while, but a few things changed my mind:

  • We’ve moved as much drawing in X-Plane to OBJs as possible and it’s been a big win. A lot of the dynamic elements are OBJs, they’re used in scenery and cockpits and airplanes. Using OBJ files means our artists (who are not programmers) can customize just about every aspect of the sim. So by providing a file format with a rich tool chain to plugins, hopefully we are helping third parties streamline content development.
  • With pixel shaders, X-Plane’s 3-d drawing environment has become complex and hard for third parties to safely augment. By encoding drawing at a higher level via pre-built OBJs (which can be animated via plugin-driven datarefs) we can insulate plugins from drawing-environment changes.
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Formats that are not changing

If you have content that worked in 864 but does not work in 9, please file a bug! Please do not assume we intentionally changed the file formats to break compatibility…I would rather get the bug report so we can fix X-Plane than have you change your work.

For every author who changes his or her work in response to a bug (an accidental breaking of compatibility), we’ll have dozens of users who find their add-ons not working but not knowing how to fix it themselves.

With that in mind, beta 16 will have two fixes:

  • Some panels were showing the default instrument backgrounds over custom panels. This will also be fixed in the next beta.
  • Lit customized overlay parts were not showing. This will be fixed in the next beta.

So if you see those bugs, please check your plane against the next beta when it comes out. If you find other problems, please file a bug!

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