Category: Scenery

2 Blog or Not 2 Blog

I figure there are three things that making blogging suited for software:

  1. A small interested group of users can subscribe to a blog without giving out an email address.
  2. The information in the blog can be found using a general search tool like Google.
  3. It’s easy for a busy programmer to post.

I think this last point is not to be ignored – I post a lot here because it’s easy enough to whip up a blog post that I can write one while the sim is booting.

The down-side of this is that blogs are not self-organizing. The blog is chronological, and somewhere within a heap of 200+ posts are detailed information on scenery topics not documented on

That’s not good. So I’ll be trying to make a concerted effort to write real permanent documentation for some of the new scenery system topics that I cover. Documentation on DDS is in the works.

Part of the problem is that my interface for updating the X-Plane scenery website isn’t that robust. One of the nice things about the plugin system being a Wiki is that it’s easy to organize and easy to edit. (And one of my frustrations with “support forums” is that they don’t self-organize…they mix questions and answers based on history and not a search key that a user might use, like “what’s wrong with my card.” We’ll be supplementing the Linux forum with a Wiki soon.)

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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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Reflections in the Wrong Place

We get a lot of bug reports showing strange reflections in the water. Some of these we can fix easily, and some will be more difficult, if not impossible. There are two fundamental constraints on the water-reflection code:

  • A reflective surface (read: water) must be approximately flat to be correct. This is just how the algorithm works. (If you want to see why a non-flat surface fails, try to draw a camera position opposite the reflection plane and trace rays through this “reflection camera”. Draw reflected objects that are close and far from the water and then observe the parallax error you get if the reflection plane curves.)
  • We need one “water camera” for each flat reflection plane. You can’t just statically offset when we have multiple elevations. (When drawing your diagrams, note how an elevation change causes a change in reflected angle, not just an offset.)

So the water will always have two problems: the earth is round (so nothing is really flat), and we can have lakes of multiple elevations (and we can’t afford to render a water reflection per lake).

X-Plane tries to get around the non-flat water problem by picking little bits of the water that are flat (and seem useful) and using them to define reflections. This algorithm will always have problems, but at least it can be tuned.

Now there are also some things that we can fix with the water:

  1. The math in beta 18 is simply wrong, something that will be fixed in beta 19.
  2. The ocean is built from polygons that are too large; this introduces approximation errors when we try to pick “a little bit” of water to use to figure out our reflection plane.

There is one more problem that I see, especially in airports like PAKT: if there are two water surfaces of different heights that are nearby, X-Plane uses a slanted water plane that tries to include both. This works very badly – the resulting slanted plane doesn’t look even remotely plausible. I’m not sure how soon we can tune this problem.

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Why You Can’t Have a Setting

I get a lot of requests for settings…the email is typically something like:

  • Some feature in X-Plane is defaulted to X.
  • I like it better when it’s like Y.
  • Can I have a setting to change the feature between X and Y.

Raymond Chen has a great posting that I think is very topical: “In order to demonstrate our superior intellect, we will now ask you a question you cannot answer.

This brings up one of the main reasons why we shy away from more settings: the more complex we make X-Plane’s configuration, the less likely it is that the average user will be able to set the sim up correctly. Settings requests usually come from our most advanced users, but we also have users who have never used a computer before. Really! I’ve been on the tech support calls – they are very nice, but way overextended on the computer side of things. Should we allow them to pick whether scenery geometry is store in AGP memory vs. VRAM?

From our perspective, having a setting that a user doesn’t understand is worse than neutral, it’s actually harmful. Every one of those settings is something that can go wrong with the sim. I removed the ability to set the level of detail bias to positive (in other words, extend the visibility distance of scenery beyond its original design) after about 500 complaints of “low framerate” from users who had maxed this setting out (causing a 4x increase in 3-d processing load) without knowing (1) what the setting was, (2) what it was good for or (3) what the down-side was.

Could we present all the info to make intelligent decisions on the rendering pages? Honestly, probably not beyond a certain point…we would devolve our sim into a lecture on working sets, bottlenecks, and the OpenGL pipeline long before the user got flying. (Wait, that’s my blog! Doh!!!) At some point the sim just has to do its best to do the right thing, or something similar to it. Just as Raymond points out that the default answer to any dialog box is “cancel”, the default answer to any rendering setting is “all the way up.”

When I tell a user who wants a setting that he or she can’t have a setting because some other user will abuse it, the answer is almost always: well why don’t you have two settings screens, a simple and advanced mode?

Besides the irony (of trying to solve the problem of too many settings with another settings), Raymond also points out that no location to hide an advanced setting is ever quite good enough. This is something we have struggled with, choosing command-line options more for to pragmatic reasons than because it’s a great solution.

This doesn’t mean you can’t ask for command-line options…I am just trying to point out some of the thinking on the other side of the coin.

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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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Water: What’s Coming Now

Beta 16 should be out relatively soon and includes what are probably the last of the water improvements for X-Plane 9.0. (All future water improvements will be in free patches or future releases.) Here’s what made it into this particular version:

  • Water wave patterns now follow the wave settings in the weather-water screen.
  • “Fetch” data from the DSFs (information about whether water is subject to ocean waves or not) is used to modulate wave patterns – go to KSAN and set the wave height fairly high. Notice how the waves die out to ripples in some of the bays.

When I last blogged about water, I hadn’t realized that we already have “fetch” data in the DSFs (and have since 820). Bear in mind that the fetch data in the current DSFs is not very good – I am sure you’ll find plenty of strange cases where there are ocean waves inland, or calm areas in the ocean. The algorithm just isn’t that good. New fetch data only comes with new global scenery.

The physics engine is not synchronized with the visual waves, although they both use the same wave height from the weather screen. The physics engine isn’t using fetch yet. I may be ale to address this in a future beta, but I’m not sure.

What I have had to punt on (for now – remember, a ton of new features come to X-Plane in the form of free patches!) is the issue of reflectivity, sparkle, and water color from various view angles. As I explained in my previous post, the way the wave pattern is filtered with view-distance causes the water to look unrealistically calm from far away. Now that we can haev taller waves this is less of an issue (set very high waves to avoid the reflective look as much as possible) but it’s still there.

I have some possible technology ideas on how to address this problem, but we don’t have enough time left in this build to go all the way with them.

One final note on water: Windows users witih Radeon HD hardware can work around the corrupt reflective water issue by running the sim with –no_fbos.

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X-Plane Water – Now and the Future

Randy forwarded me a very detailed email message from the features list about water. First a few notes:

  1. I don’t read the features list – I’m only blogging this because Randy forwarded it my way.
  2. Procedural water (that is, procedural waves with the sky as a reflection) is a default shader option because when we first looked at it, it seemed to be “low cost”. Some hardware really chokes on this option. But one trend that’s clear: I have not seen any hardware that can do volumetric fog but has trouble with water. When it comes to expensive computations, vol-fog is the the heavy effect. If your card can run with vol-fog even remotely well, you’re not going to get any kind of fps boost by turning off water. So the question of whether procedural water can be optional is one of whether the water looks good (which I will discuss below), not one of performance.
  3. I’ve received plenty of emails about how we can “cheat” on the reflections to make them faster. To be honest, these ideas aren’t very useful…you really need to know how the rendering engine works on a low level to find good ways to cheat on reflection quality.

(It’s not enough to make the reflection texture less good looking, you have to do so in a way that makes it take less time to render! We’ve basically already taken all the optimizations we can – that’s what that water reflection detail popup does. Keep it on a lower setting.)

So with that in mind I’d like to bring up three issues with the reflective water and give you some idea of the roadmap. I should say that when I list features as coming in the 9.xx or 10.xx time frame what I really mean is: some depend on new global scenery and some do not. It’s possible that we may do a ton of water work in 9.1 or we may not do any more for five years. I can’t really make a good prediction on future features after 9.0, except that they’ll be, um, really cool. 🙂

Water Weather Settings (9.00)

X-Plane currently provides a global wave height setting. X-Plane 9 beta 15 ignores this setting and simply creates calm water. This is simply a link-up between the physics and the shader that I had not gotten to until now. I believe that beta 16 will address this; the water wave height will match what you dial in. This still is only a baby step, but there will at least be a workaround for the mos common complaint (the ocean looks like glass) in that you can set the wave height to 10 meters.

Water Properties (9.xx, 10.xx)

Now Peter brings up an important point: the properties of how the water look vary with their location. First I must point out an architectural issue: you can’t do a great job of computing “fetch” (open runs where wind builds up waves) in the sim because the area adjacent to the current water may not be loaded. That is, if X-plane doesn’t have the pacific ocean loaded, how can it know that the waves hammering San Francisco can be pretty big? So I have always viewed fetch as something to pre-compute into a DSF mesh.

(This does bring up an architectural issue…how can we have properties on open ocean with no DSF mesh? The answer might end up being that we do have to provide water-only DSFs for bays and inlets that are large enough to cover a whole tile.)

Now it turns out that (secretly) the DSFs have contained a very crude version of fetch since 8.20. In version 8 we didn’t really have the shading power to visualize it (I did have some experimental code once) and in version 9 it is not yet hooked up. The fetch calculation isn’t very good, but it does exist. In the long term, we’ve talked within the company about including bathymetric data (water depth) and even water properties like clarity and the color of the goo in the water. Improving the water metadata would be a next-global-scenery feature, and we don’t recut global scenery very often.

(The DSF format is flexible…you can encode just about as much extra data into the mesh for water as you want – it’s not a format change.)

So I think you may see some improvement in the water as we utilize existing fetch data in the mesh, and some improvement as we encode more meta-data into the mesh. Note that to do any of this we need to change the sim a bit…right now it assumes a constant wave height – this would no longer be true. I think these kinds of improvements will start during the 9.x run but not be in 9.0.

Filtering Errors (9.xx)

This is the most technical issue with the water, relating to how the graphics hardware works. The problem is that the way the far-view of the water is computed is too reflective due to down-sampling.

In real life, if I am in front of a body of water with 6 inch waves, I will see two things:

  1. Near me, I will see the waves themselves. Part of the waves will be dark, because their surface normal faces me, so the Fresnel equation says I see down into the water, where I see the bottom (or if it’s deep enough, darkness). Part of the waves will be at an angle to me and act reflective, picking up colors from the sky and maybe surrounding terrrain. So my waves are going to be a mix of the sky color and some kind of dark color, with the color contrast allowing me to see the shape of the wave.
  2. Farther out, the waves will be smaller than my eyes can distinguish and I’ll start to see a more consistent water color, which is a mix of all of the various sky color inputs and darkness. The particular mix might depend on the chop and shape of the waves and angle to the sky. The important thing is: there is scattering of the reflection at a level smaller than my visual acuity, so I see sky color, but I don’t see a sky reflection, and that color is darkened by the Fresnel equation.

Now in X-Plane the problem is this: the water waves are built up procedurally from a noise texture. As we get farther away, that wave texture is reduced in quality. Unfortunately, the graphics hardware averages together the wave shape, not the resulting color from the wave shape.

So instead of getting sky + deep = darker blue for the water, I get peek + trough = flat water! In other words, at a far distance the waves are canceling each other out before color lookup, giving us a perfect mirror in the far-ground.

This is fundamentally an implementation problem – I bring it up only because it’s a counter-intuitive one. In the immediate future, the “glass lake” problem will become less because filtering only kicks in like this when the waves become less than one pixel – with the option for taller waves coming, the waves should be visible farther out. In the longer term we’ll probably put in new shading code to address filtering problems.

Reflection Positioning Bugs (9.0, 9.xx)

As of beta 15 I thought I had fixed most of the reflection positioning bugs (that’s what happens when something reflects in the wrong place in the water) – the geometry for this is made complicated by the Earth being round. I don’t expect to nip all of these bugs in 9.0 but I do hope to get most of them, and I will keep working on this as bug reports come in.

Wave Shape (9.xx)

Finally, our wave shapes are quite primitive – it’s just shaped procedural noise designed to look tolerably like water. We have a framework into which we can insert more complex wave equations (at the cost of some framerate). I don’t know what the future will bring in this area. The v9 water sets out a new foundation onto which we can do more complex water. But we have to crawl before we can walk.

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A New Broken Record

For years now I’ve been harping about ways to keep the number of batches down in your scenery. A batch is a single submission of triangles to the graphics card for drawing. Batches get rendered fast even if they contain a ton of triangles, but changing modes between batches is not very fast, so a few large batches is hugely better for performance than a large number of tiny batches.

To play that broken record one more time, there are two ways that you (a scenery designer) can cut down the number of batches):

  • Use a small number of larger textures instead of a large number of small textures, preferably sharing textures between similar scenery elements that are placed nearby. X-Plane will do its best to merge the content that uses those textures into single batches. We call this the “crayon rule.”
  • Use less attributes in your objects. Attributes usually require a new batch (after the graphics card mode has been changed due to the attribute). So if you’ve got 1000 attributes in your object, you’ve got a problem.

Well, with X-Plane 9 I have a new broken record: avoid overdraw!

Overdraw is the process of drawing pixels on top of other pixels on screen. It happens any time we use blending to do translucency, and any time we use polygon offset to build the image in layers.

Overdraw is bad because with X-Plane 9’s pixel shaders, most users are slowed down by the graphics card’s ability to fill in pixels (pixel fill rate), with those complex shaders being run for every pixel. If you are at a screen-res of 1200×1024 looking at the ground with no objects, that might be 1.2 million pixels to fill. But if there is an overlay polygon covering the ground, we have 2.4 million pixels to fill! That’s a huge framerate hit.

Right now there’s not much you can do about overdraw. Once MeshTool comes out I will post some guidelines on how you can limit overdraw.

We took a step in the v9 global scenery to limit overdraw: in X-Plane 8 the global scenery tried to hide repetition of flat textures by drawing them over each other with offsets. In X-Plane 9 this is done in a pixel shader (e.g. the texture is analyzed and swizzled in the shader and then drann once), cutting down the number of times we must draw.

If you turn pixel shaders on and off in a flat area like Kansas you might see this if you compare the screenshots – the farm textures are more repetitive without shaders. This gives faster fps to everyone (with or without shaders) by eliminating overdraw.

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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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