Category: Aircraft & Modeling

Broken Panels

I have found the cause of a rather serious bug in Plane-Maker: sometimes instruments disappear from the hierarchy (but are still visible in the main window).

The problem is that the cut-paste facility, when used with multiple-instrument selections, was corrupting the hierarchy information.  Because of the way instrument hierarchies are managed, this corruption persists – even if it isn’t visible.  So if you manage to ungroup everything, it looks okay until you work more, then the instruments disappear again!
This is a really bad bug of mine, particularly since a panel is such a time investment.  Here is what we’ll be able to do in 930 to get around this:
  1. A new “flatten panel” command simply ungroups everything and completely cleans the hierarchy.  All corruption of hierarchy is fixed with this command, finally exposing every instrument.  From that point on, you can then re-group and things should be okay.
  2. I am fixing the cut-paste commands to not trash the hierarchy, and I am looking for any more hierarchy-corruption problems.
  3. 930 has export/import of instrument groups to text files.  So another way around instrument corruption problems would be to export the panel to a text file, fix the grouping problems (which is a matter of moving the GROUP/END_GROUP lines) and then re-importing.  If you do not have a selection, the entire panel is exported, including any hidden items in the hierarchy.

I believe that text-based panel import/export will also be useful for sharing individual instruments (or clusters of grouped generic instruments), archiving work, and making large-scale changes using search-and-replace.

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Two Squashed Bugs for 930

These two issues have been discussed a lot in the forums, so I thought I’d mention them:

First, I finally found and nuked that star-burst pattern in the rain.  It turns out that for some textures, compression was destroying the lower res mip-maps, causing the geometry that the rain drops are drawn on to show up as that starburst pattern.  It should be fixed for 930 beta 1.
Second, it turns out that the code that converts the 900-format generic instruments to 920-format generic instruments* was being run on the user’s airplane whenever a multiplayer airplane older than version 920 was being run.  That could cause generic instruments to disappear, appear incorrectly, or just crash the sim, because the aircraft data in the user’s plane (once the user is flying) is already in 920 format…if you interpret it as 900 format again, you get non-sense.  
I am fixing this for 930 beta 1; there may be other bugs relating to multiplayer and generics, so we’ll see if this fixes most of the problems, or others crop up.  The panel system is essentially “global” (that is, there is one panel for the user in all of x-plane) but the instrument data is per-plane…so there is always a risk of code mistakes where the multiplayer planes affect the user’s panel.
When will 930 beta 1 be out?  I don’t know.  Hopefully pretty soon – when bug fixes make it into the blog, we’re usually in the push to get to beta.  But I’m working on features on a few fronts, so it’s hard to say which ones will be done first.
* X-Plane 920 revised the ACF format from version 900.  The file format for generic instruments was pretty much completely changed to accommodate new features like key frames.  920 has code that converts the 900 generic instruments into 920.  For example, simple key frame tables are built out of the older offset-scale parameters per instrument.
Posted in Cockpits, Panels by | 2 Comments

Panel Texture and Panel Clicking

As of X-Plane 9, life was simple: ATTR_cockpit and ATTR_cockpit_region caused your triangles to be textured by the panel, and they could be clicked. ATTR_no_cockpit went back to regular texture and no clicking.

Well, it turns out that secretly ATTR_cockpit was two attributes jammed into one:
  • Panel texture – that is, changing the texture from the object texture to the panel texture.
  • Panel clickability – that is, mouse clicks are sent to the 2-d panel and act on those instruments.

With X-Plane 920 and the manipulator commands, this “clickability” aspect is revealed as a separate attribute, e.g. ATTR_manip_none sets no clickability, and ATTR_manip_command makes a command be run when the triangle is clicked. These attributes can be applied to any kind of texture – panel texture or object texture.

So how does ATTR_cockpit work in this context? Basically you can think of ATTR_cockpit as two “hidden” attributes:


and similarly, ATTR_no_cockpit is likeATTR_texture_object

With this you can actually get any number of combinations of attributes, but the code is sometimes unexpected. In particular: if you want a manipulator other than the panel or none, you have to specify it again. Example:# set command manip
ATTR_manip_command hand sim/operation/pause Pause
TRIS 0 3
# we now have to reset the cmd manipulator!
ATTR_manip_command hand sim/operation/pause Pause
TRIS 3 3
# we have to reset the cmd manipulator again!
ATTR_manip_command hand sim/operation/pause Pause
TRIS 6 3

Similarly, if you want the panel manipulator, you may have to reset the cockpit!ATTR_cockpit
TRIS 0 3
# now make the mesh not clickable
TRIS 3 3
# Mesh clickable again
TRIS 6 3

The good news is: this isn’t nearly as wasteful as it seems. X-Plane’s object attribute optimizer is smart enough that it will remove the unnecessary attributes in both cases. In the first one, what you end up with is one manipulator change (to the command manipulator), and the panel texture change is done without changing manipulator state at all. In the second case, you end up with the manipulator change, but the panel texture is kept loaded the whole time.

In other words, even though the double-attributes or duplicate attrbibutes might seem to be inefficient, the optimizer will fix them for you.

One reason you might care: the cost of panel texture is one-time – that is, you pay for the size of the panel texture once per frame. But the cost of manipulatable triangles is per-triangle! So having more is bad. With ATTR_manip_none, you can use the panel texture but not have it be clickable, which can be a big performance win.

930 will handle manipulatable triangles a lot faster than 920 — but that’s still not a good reason to have all of your triangles be clickable!

This article is still unfinished, but I am trying to put together some info on how to detect performance problems like too many clickable triangles.
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Which is Faster: Panel Texture or 3-d Instruments

There are two ways to make 3-d instruments in your 3-d cockpit:

  • Create 2-d instruments on a panel and use the “panel texture” (ATTR_cockpit or ATTR_cockpit_region in your OBJ) to show those 2-d instruments in the 3-d cockpit.
  • Model the instruments in 3-d using animation.

So…which gives better framerate?  Well, it turns out that they are actually almost the same…a few details:

  • If your card can’t directly render-to-texture, there is an extra step for the panel texture. But that would be a weird case – all modern cards can render directly to textures unless you have hosed drivers.
  • For very small amounts of geometry, there’s pretty much no difference between rotating a needle using the CPU and telling the GPU to do it by changing the coordinate system.
  • The panel texture does put pressure on VRAM – if you’ve had to go to a 2048×2048 panel texture to have enough space, it’s going to hurt you.
Both approaches are actually quite inefficient – you get best vertex throughput on the card when you have at least 100 vertices per batch.  But if a panel has 800 batches, you don’t necessarily want to do this – you’d pick up 80,000 vertices just trying to “utilize” the graphics card.  That’s not a huge number, but it’s big enough to consider.  Panels have enough moving parts that they’re going to push the CPU more than the GPU.

A number of authors like the 3-d approach because they are more comfortable with 3-d tools, and because it can look sharper (since there is no intermediate limiting texture resolution). 

There is only one case where I would advise against the 3-d approach: if it takes a huge number of animation commands to accomplish what can be done in one generic, use the panel texture; the generic instruments are all coded cleanly and none of them take that much CPU power.  But some of them produce effects that would be relatively difficult to reproduce with animation.
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Fixing Panel Editing in AC3D

The X-Plane export plugin for AC3D doesn’t handle panel textures very well.  The current plugin tries to identify cases where you have used your panel background as a texture – this queues it to generate ATTR_cockpit.  This scheme has a number of problems:

  1. The search paths for the panel background are not up-to-date.  The plugin doesn’t know about the new naming conventions or the cockpit_3d folder.
  2. The scheme doesn’t address panel regions at all – there is some support for them but it doesn’t work well.
  3. Most important: panel editing is not WYSIWYG.  Since you are using the panel background as your texture, you can’t actually see where all the moving parts are!  Doh!

That last point is perhaps the most important one, and it is why, for the next version of the plugin, I am introducing panel previews.

Basically a panel preview is a screenshot of your panel with the instruments on it, sitting in your cockpit_3d/-PANELS- folder.  AC3D will recognize and use the panel preview when possible.  This will solve problems (1) and (3) – there will be only one naming convention for previews, and they will be screenshots of the panel in action, so you can texture with a preview of the instruments.
Plane-Maker 930 will contain a facility to generate panel previews; if you are using X-Plane 920, you can generate the preview manually by taking a screenshot in X-Plane.
For panel regions, we will have one preview file for each region (e.g. Panel_preview0.png, panel_preview1.png).  This addresses issue 2 – usage of the region previews will invoke ATTR_cockpit_region.
Finally,  I am moving the panel sub-region information from the preferences to the .ac file (hopefully) so that it will be saved with your plane.
Hopefully this will make a work-flow which is much simpler.  To make a 3-d cockpit you will simply pick “generate previews” in Plane-Maker, and then start using the previews as textures.
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Al Bedo Makes an Omlette

Sometimes you have to break a few eggs to make an omlette.  Or at least, you have to consider whether breaking them is acceptable.  Often I hit cases where the cost of supporting a legacy feature is somewhat painful.

One way to decide what to do is to change the feature early in beta, see who squawks, and then change it back if necessary.  There are two I am looking at for 930.
Glass Instruments
It turns out that glass instruments fade to black, not to transparency.  This is a little bit weird, because that means they will leave black footprints if they are on top of a non-black background.  My guess is that most people use them on black screens and thus did not notice.
If people really need fade-to-black glass instruments, I’ll just create a new lighting type (glass-transparent), but if everyone can live with fading to transparent, it’s certainly the more useful case and probably what most people always wanted.
Separate Specular Hilights
For as long as I’ve been involved, X-Plane’s specular hilights are modulated by the object or airplane texture color.  In other words, if you paint your airplane red, you get red hilights, and if you paint it black, you get no hilights at all.
This is not a very good way to do things for a few reasons:
  • Under this scheme, you can’t make a shiny black object.
  • Someday we will add gloss maps – but the glossy part of the gloss map will be defeated by the black texture.

So for 930, I am looking at not modulating specular hilights by texture.  (This is called “separate specular hilights” in OpenGL lingo.)  My guess is that they will look enough better in almost every case that people would rather have it this way.

Should specular hilights be white for a black object?  Yes!  A specular hilight is a simulated intense reflection from a very far away, very bright object (the sun).  So it should take its color from the sun, not the object itself.  To this end, I have also (finally) set the specular hilights to take on the daylight sun color, so that they get fainter and yellowish at dusk.  This makes dusk and dawn look a little bit less strange.
(Nerd note: Technically, for the day texture to be an albedo texture, it shouldn’t affect specular hilights.)
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Who Is This Al Bedo Guy Anyway?

That’s Mr. Bedo to you!

Sometimes I end up learning the name for a computer graphics idea or technique long after I use it. So I was amused the other day to find out that the fancy computer-graphics name for the “daytime” textures in X-Plane (you know, the normal ones for OBJs and airplanes) are called albedo textures in technical terms – or rather they define the albedo component of the lighting equation.

This is handy because I had a nice big fancy word for _LIT textures: emissive. So now, armed with both technical terms, we can accurately describe the two parts of lighting that X-Plane usually specifies by texture: albedo and emissive.

Basically the albedo texture tells what color you see when light shines on it (or rather, how much of that light is reflected back to the viewer diffusely) – it represents color information that does not generate its own light. The emissive texture describes light created by the object, and thus visible under any circumstances.

X-Plane’s lighting equation is thus typically:

albedo * brightness at that point + emissive

Where “brightness at that point” is the sum of all of the lighting effects from any number of lights, the sun, ambient light, etc.

Now there is something interesting about this lighting equation: the emissive component is added to the “modulated” albedo component. So what happens if:

  • Albedo is 100% (that is, white)
  • The brightness of the sun is 100% bright (really bright day) and
  • Emissive is non-zero?

Answer: the total lighting is more than 100%!

100% of what? These lighting values are described in terms of the range of color your monitor can output, from black (0%) to white (100%). So if we have a lighting value of 120%, basically it shows up as white (100%) and the “extra” white is lost. The result is a loss of color accuracy and detail.

For 930 I have a to-do item to scale down all emissive light by a constant factor when the day time overall brightness is high.

The idea is this: in the real world, your eyes have non-linear, adjustable sensitivity to light (and the sun is really, really bright). So when the sun is out, the amount of light added by a neon sign is trivial compared to the light already on the sign from the sun. At night the sign’s light is much more significant because it is relatively dark (thus the sign is in a more sensitive part of your vision and your eyes are adjusted).

In X-Plane, scaling down the emissive texture during the day will simulate its lesser effect during the day.

One more note on emissive vs. albedo texturing: ATTR_emission_rgb basically sends a certain portion of the day time (albedo) texture to the emissive part of X-Plane’s lighting. But the emissive (LIT) texture is still used. So if you use ATTR_emission_rgb, don’t set the emission level to full (1.0 1.0 1.0) and use a very bright _LIT texture; the result will be more than 100% brightness.

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Contractual Ranting

Microsoft extended Windows XP sales yet again, more or less.  But rather than rant about how the Vista user experience makes me want to tear my fingernails off or how brain-damaged it is to try to put DRM into drivers, let me instead focus on Windows as an example of the cost of contracts.

I have ranted in the past about how the boundary between X-Plane and a third party, or the plugin system and third parties, or even two third parties, is a contract.  Consider:
  • The named light list forms a contract between X-Plane and objects, e.g. X-Plane guarantees that there will be a named light called “airplane_landing” and that it is a good choice for landing lights.  (This implies that X-Plane won’t change what it looks like to be inappropriate for landing lights, and that third parties won’t use it for inappropriate uses, like airport apron lights.)
  • XPLMGetDataf forms a contract between the plugin SDK and plugins, guaranteeing that there will be a function in the XPLM called “XPLMGetDataf” that takes a dataref and returns its value.  (This implies that Sandy and I won’t rename it or change its arguments or remove it all together, and that plugins won’t pass non-datarefs in as arguments.)
  • Even a paint kit forms a contract – the airplane maker is essentially saying “the tail will be mapped to the upper left of the texture, and I won’t remap my UV” and the livery maker is saying “I will put an image in the upper left corner that looks like a tail.”

By comparison, the clouds are not a contract – there is no way third parties can customize the look of the clouds, so we can change the algorithm by which we create them pretty much at will. We could switch to a volumetric approach for all clouds or even go back to 2-d without worrying about third party interaction.

Okay – that’s a lot of words about contracts…what does that have to do with Vista?  Well…
The Cost of Changing the Contract
Two major aspects of why Vista has been a worse experience for users than Windows XP come directly to the need for Microsoft to change contracts.
  • For years, applications have run on Windows with admin rights.  This is not good – it means that any process can do serious damage to the system if hijacked – and on Windows processes get hijacked on a fairly regular basis!
  • For years, audio and video drivers have run pretty much unprotected.  This was good from a performance perspective, but also caused a lot of BSODs.  On Windows, drivers are third party components and are quite possibly not checked by Microsoft (especially video drivers) so letting them run without protections is risky.

In both cases, the problem is that the old contract is both (1) poorly designed* and (2) being used by a lot of third parties.  What choice did Microsoft have?  Continue to let apps run in admin mode and hijack the whole machine any time the user picked up a virus?  Or change apps to run in user mode and hope that the applications didn’t depend on this guarantee?

(At this point, Raymond might go ballistic and point out that the Windows API doesn’t really promise admin rights and apps should not have been doing all of these naughty behaviors in the first place.  I don’t know what the Win32 API declares…the difference between what a platform declares and what it does is important enough to warrant another post.  Certainly with X-Plane we have to worry a lot about third parties depending on behavior that was unintentional but turned out to be useful.)
Vista has been a difficult transition because it changed a bunch of rules (that needed to be changed).  In the long term, I am sure that both of these decisions are for the better — eventually applications won’t be counting on administrator rights, so we won’t have to fume about UAC (or shut it off), and a hijacked web browser won’t be nearly as dangerous.
On the video driver front, the Vista experience is pretty reasonable now – there has been a lot of improvement since Vista first came out.  I expect applications and UAC to take a lot longer – video drivers get revised quite frequently; applications seem to linger around forever.
I’m Not Signing That
If we end up with a situation like this in X-Plane (the contract is used heavily by third parties and not well designed) we only have two options, and they’re both bad:
  1. Break the contract.  Third party content stops working, users are angry, authors are angry.
  2. Stick with the contract and mitigate as best we can.  Usually this means writing more code (slows down new features), using a less optimal implementation (lowers frame rate), etc.

This is why my first reaction to any file format extension is: “is this going to be a PITA in a year”?  The benefit might be visible now, but the cost could plague us indefinitely.

What You Want, Not Where You Want It
If you would like to request a feature, tell me what you want, not where you want it implemented.  I bring this up because many of the feature requests I get are very specific and describe an implementation, not a goal.  (To draw an analogy, it’s as if I call a general contractor and say “dig a big hole right here” without telling him “it is for a swimming pool”.)
The reason “what not how” is so important is because many of the “how” implementations that people send me involve creating new contracts with third parties.  I am going to try to design the feature with the minimum contractual obligations – that is, to do just what is intended and hopefully not much more.  
But if I can’t tell what you are trying to do, I can only say “I won’t code this implementation – the cost of long term support due to contractual obligations outweighs the usefulness.”  It might be that there is another way to implement the feature that would not put a long term burden on the scenery system or airplane SDK and still provide all of the benefits.
* Poorly designed?  Or perhaps well designed for a previous problem – if the problem changes, the design might not be appropriate.  Or perhaps not even designed at all – sometimes contracts evolve without a lot of central planning.  All of these things have happened in X-Plane.  In the case of Windows, I suspect it’s the previous-problem case — that is, what made sense for much smaller computers where the scope of what could be done was quite limited no longer makes sense for big modern computers that are capable of a more expensive and robust solution…just my speculation.
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To Wiki or Not To Wiki

You might not believe this (due to the general lack of scenery system documentation) but I do spend some brain power thinking about X-Plane documentation for third parties!

Consider two approaches to documentation:

My question is: which of these approaches is more “readable” or “clear” to you as a third party? Each one (the formal website vs. the Wiki) has pros and cons, but I can’t judge “usability” of the documentation myself.  Is it easier to find things on the website?  On the Wiki?  Comments welcome!

(I need to decide where to put future documentation, hence the question “which works better for those who read the documentation.)
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More Aircraft RFCs – Landing Lights

It looks to me like we could afford a few landing light halos on most (but not all) hardware.  This gets a bit tricky in terms of how we make this available to authors…

  • We have to allow access without breaking old planes.
  • There will be two distinct cases due to very different hardware.

So…I have posted an RFC on the X-Plane Wiki.  Please post your thoughts on the discussion page!

One option (not really discussed in the RFC) is to do nothing at all.  Basically I hit upon this during some routine refactoring of the shaders.  The whole issue can be deferred indefinitely.
Why wait?  Well, I don’t believe that an incremental increase in the number of landing light halos is the future.  Our end goal must be some kind of truly global illumination, hopefully without a fixed lighting budget.  It may not make sense to add a bunch of complexity to the aircraft SDK only to have all of those limit become unnecessary cruft a short time later.
(I think I can hear the airport designers typing “why do the airplane designers get four lights and we get none?  Give us a light or two!”  My answer is: because of the fixed budget problem. We can allocate a fixed budget of lights to the user’s aircraft because it is first in line – we know we either have the lights or we don’t.  As soon as we start putting global lights in the scenery, we have to deal with the case where we run out of global lights.  For scenery I definitely want to wait on a scheme that isn’t insanely resource limited!)
Programmers: yes – Dx10 hardware can do a hell of a lot more than 4 global lights.  Heck – it can do a hell of a lot period!  For example, it can do deferred rendering, or light pre-rendering. A true global lighting solution might not have anything to do with “let’s add more global lights a few at a time.”
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