I have been trying to put documentation on the X-Plane Wiki, and use this blog for announcements and “the inside story”, rather than letting the blog turn into a poor-man’s users manual. An aircraft developer asked me via email whether there was a blog entry on some of the pitfalls of the v9 panel lighting system. There is not, and the lighting system is under-documented. I will be working on improving the documents over the next few weeks, but the point of this blog entry is: “how did we get here?”
I am a huge fan of incremental software improvement. That’s the subject of another blog post (perhaps on another blog), but for now I’ll say this: all changes to the rendering engine since version 8.0 have been incremental ones, and yet if you were to look at the code, you wouldn’t see a series of band-aids taped on top of each other. Each incremental change leaves the rendering code “fully updated”, as if it had been written yesterday. I start each new scenery feature by first reshaping the existing code into the most useful form for what we want to have in the future, and then coding the new feature is relatively simple.
But this strategy has an Achilles heal; if the code being refactored has a public interface (whether it is a file format or programming API), then all of the intermediate steps in the journey become requirements for future products in order to maintain backward compatibility.
This is not a problem as long as the programmer knows where he is going. The danger comes when one of the intermediate steps is actually a step in the wrong direction, and becomes dead weight around a future design.
A Reasonable Progression: OBJ
The OBJ 800 file format has had a reasonable progression* since its birth in version 8. It has gained a number of new features, but each one has generalized and made more powerful previous ideas, such that “legacy behaviors” are not so painful. Some examples:
- Hard surfaces may now be decks (e.g. you can fly under them) or not, and you can specify what kind of hard surface you have. The original hard surface command was simply “it’s hard” or “it’s not”. But viewed under the lense of the new scenery system, that old hard surface command implicitly implied “the surface is smooth” and “the hard surface is not a deck”. So the new hard surface command is a more general version of the old one, which continues to work under the new system.
- Animations in version 9 can be key framed; in version 8 you simply specify start and end values. But start and end values are just like having two key frames. So viewed under the lense of the new scenery system, all animations are key framed; older objects always just have two key frames. The new key framed commands are a more powerful, more general version of the old ones.
I can’t say that the relatively pain-free evolution of OBJ files over the last 4 years comes from good design or genius on my part – in truth it’s probably just good luck. But I think one thing has helped me keep the new OBJ extensions relatively sane: most of them are conceived several months before they make it into X-Plane.
I have a scenery system to-do list that will last me at least another four years; most of it is filled with things that Sergio has asked for. This to-do list acts as sort of a road map for future scenery system extensions; for any possible OBJ change, I can look at it relative to the other todo items and ask: “is this extension going to play nicely with things to come?”
(As a side note, this is one of the reasons why there are not light maps in any of the X-Plane modeling formats. Light maps don’t play well with a number of other scenery system extensions. I want to resolve the conflict between these future additions before they go into the sim.)
Wandering In the Desert
By comparison, the evolution of the panel system in version 9 has been more like wandering in the desert than a straight line toward a goal. Repeatedly, I put features into the panel system without a clear roadmap of where we would end up or how they would work together. The result is what you see now when looking over the panel documents: complexity and chaos.
Basically there are several major changes to the panel system that affect each other in strange ways:
- A more complex lighting model on the 2-d panel in version 920. (That is, the 3 2-d spot lights, and generic instruments with back-lit, mechanical, or glass lighting.)
- A more complex lighting model in the 3-d cockpit in version 930. (That is, 3-d spot lights, ATTR_cocpkit_region and generic instruments with back-lit, mechanical, or glass lighting.)
- A separate panel used only to provide texture to the 3-d cockpit. (That is, the 3-d panel.)
The problem is the order that they were invented: first ATTR_cockpit_region, then the 3-d cockpit, then back-lit generic instruments, then 2-d spot lights, and then 3-d spot lights.
The result is two sources of confusion:
- Some combinations of features simply don’t work together. Since all of the features appear to be independent, I sometimes get bug reports on these. For example, you can’t use the 2-d spot lights on the 3-d panel. This is not a bug, it is by design! I will explain why some of these limits exist in future blog posts.
- Among the remaining combinations that do work together, there are a lot of choices about how to structure a plane – too many choices!
This second point is a tricky one: X-Plane has to continue to support whatever set of features was available for any given release (864, 900, 920, 930) so that older planes continue to work. But some of those combinations (e.g. the ones that exist in version 900) don’t make a lot of sense for new planes made in 930.
I am open to ideas on how to solve this. I intend to document a “correct formula” for a modern plane, perhaps with tutorials, on the Wiki. I am also considering programming Plane-Maker to flag unusual combinations of features as a warning when saving 930 planes.
Either way, I fear I’ve learned my lesson from the panel system: incremental improvement of code is only a good idea if the programmer knows where he is going! Next time I will use Google Maps. 🙂
* I suppose that whether you think the OBJ 800’s evolution has been reasonable depends on your standards for file formats. OBJ 800 absolutely does show growing pains. I would only say: consider the number of revisions and the change in the hardware platform OBJ 800 feeds when you consider its stretch marks.
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:
- 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.
- I am fixing the cut-paste commands to not trash the hierarchy, and I am looking for any more hierarchy-corruption problems.
- 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.
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.
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:
- 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.
- The scheme doesn’t address panel regions at all – there is some support for them but it doesn’t work well.
- 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.
I have blogged about this before, but I will try to create one simple explanation of what’s going on with sim/cockpit2 and sim/flightmodel2 datarefs.
Sandy and I (with the help of others who helped compile the list) created “new” datarefs (first released with X-Plane 9) , aimed at airplane modelers. These new sections are:
- sim/cockpit2/ which provides a new set of datarefs for cockpit modeling via OBJ animation and generic instruments.
- sim/flightmodel2/ which provides a new set of datarefs for airplane exterior modeling via OBJ animation.
These datarefs sometimes include new data that was not available in version 8, and sometimes they simply provide a second dataref with the same information. Why duplicate datarefs? The new datarefs have some special properties, so I wanted to have a complete set of datarefs for modelers with these new properties.
Skip to the end for the rules of thumb on how to use them.
Clean Naming
The new datarefs are designed to have longer, less confusing names; the old datarefs contained a lot of abbreviations – potentially acceptable for programmers (who are used to seeing things like fstat and chgrp on a regular basis) but not good for modelers who do not speek English as a first language. The new datarefs have long names and are more consistent in their conventions. They also contain complete documentation.
Array Sizes
You will see the array dimension of some of the new datarefs as symbolic constants, e.g. [engine] instead of [8]. This is because the dataref generation system we use knows that these new datarefs sometimes track the maximum number of parts in the aircraft structure. This tagging means that it is much simpler for Sandy and I to adjust the datarefs when Austin increases part maximums.
With the old datarefs, if Austin allows for 10 engines, Sandy and I must search for every [8] dataref and decide if it must be [10] – some will be per-engine and need to change, some will be per-battery and will not! With the new system, we simply redefine the “engine” constant to 10 and the datarefs adjust.
(Note that if your plugin really needs to run dynamically with any number of engines, the best thing to do is to read the array size using XPLMGetDatavX.)
Failure Support
There are two ways to view a dataref: before system failures (such that the dataref reflects simulated physical reality) and after system failures (such that the dataref reflects pilot indications). For example, when the pitot tube ices up, the pre-failure airspeed reflects how fast you are flying; the post-failure airspeed reflects how much crud is in your pitot tube.
Pre-failure datarefs are appropriate for animating the exterior of the airplane. For example, if the gear indicator light fails but the gear is working, you want to animate your landing gear based on the real (pre-failure) gear position, so that the gear really does look like it’s down from an outside view.
Post-failure datarefs are appropriate for animating the cockpit. For example, you want to use that post-failure indicated airspeed for your air speed indicator, so that pitot ice will affect your generic instruments and animations, as well as the built-in instruments.
The new datarefs are designed to clearly provide two different views:
- sim/cockpit2/ are all post-failure whenever possible, and are thus appropriate for cockpit modeling.
- sim/flightmodel2/ are all pre-failure, and thus are appropriate for external airplane modeling.
Be careful not to swap them! You should always be using sim/flightmodel2/ for your aircraft and sim/cockpit2/ for your cockpit. If the dataref you need is in one and not the other, email me and I will add it to the right place.
Correct Multiplayer Behavior
The older datarefs all return data about the user’s airplane. However if you build an object, attached to an ACF, and that ACF is loaded for a multiplayer plane, you will get incorrect results — the user will see his own plane’s actions visualized on the multiplayer plane.
The new sim/cockpit2/ and sim/flightmodel2/ datarefs handle this case correctly: they return data about whichever airplane is being drawn. Thus if your object is attached to airplane number 5 in a multiplayer session, that’s the airplane that will animate your control surfaces.
(Plugin developers – outside airplane drawing, these datarefs return information about the user’s flight.)
For this reason, you should always use sim/cockpit2/ and sim/flightmodel2/ – not the older sim/cockpit and sim/flightmodel/ datarefs. If the dataref you want is only in the old sections but not the new ones, email me!
What Dataref Do I Use?
Here’s the rule of thumb:
- If you are targeting X-Plane 6/7/8, you must use sim/cockpit and sim/flightmodel, otherwise
- If you are targeting X-Plane 9, use sim/cockpit2 for your generic instruments and 3-d cockpit. Use sim/flightmodel2 for your attached objects.
That’s all there is to it!
The choice of panels (2-d panel vs. 3-d panel) for your cockpit and the choice of OBJ commands (ATTR_cockpit vs. ATTR_cockpit_region) both affect how your 3-d cockpit looks. Since these two techniques can both be varied, there are a lot of combinations, and 920RC2 does not have the right behavior. (RC3 will fix this I think.)
2-d vs. 3-d Panel
The 3-d panel is a new flat panel whose purpose is to provide the image for ATTR_cockpit or ATTR_cockpit region. Building a new panel for 3-d has a few advantages:
- The instruments can be packed together – no need for windows or other texture-wasting elements. This can help reduce panel size — panel size is expensive when using ATTR_cockpit_texture.
- The 3-d panel can be smaller than the 2-d panel; having a huge panel feed the 3-d object is slow.
- Instruments that are drawn with perspective in the 2-d panel can be redrawn orthographically, which is more useful for texturing real 3-d overhead panels.
Because the 3-d panel is meant only to be used as part of a 3-d cockpit object, spot lights and flood lights are not available, nor is a night-lit alternative. Why not?
- Such customized 2-d lighting would not match the rest of the 3-d cockpit visually.
- We will eventually have a more global lighting solution.
Basically I don’t want to provide features that will clash with the future implementation and eat framerate! The 3-d panel is aimed at next-generation content.
ATTR_cockpit vs. ATTR_cockpit_region
ATTR_cockpit_region provides a new alternate panel texturing path that gets rid of legacy behavior for improved performance and image quality.
- ATTR_cockpit_region requires the region be a power of 2, which saves VRAM. (If your panel is 1280×1024, then ATTR_cockpit rounds it to 2048×1024. Yuck!)
- ATTR_cockpit_region grabs the lit and unlit elements of the panel separately, and can thus provide lighting that is consistent with the rest of OBJ.
- ATTR_cockpit_region does not preserve transparency (which isn’t a good way to model a 3-d cockpit performance wise) – removing the alpha feature improves framerate and saves VRAM.
- ATTR_cockpit_region lets you pick out parts of a panel to texture only what you need.
This last point is less important now that we have 3-d panels (ATTR_cockpit_region came first) – it was meant to let you pick out a small subset of a large size 2-d panel, skipping windows. But if, for example, you need more than 1024×1024 pixels of panel texture, two cockpit regions are better than one 2048×1024 – some graphics cards hit a performance cliff when a cockpit or region exceeds 1024×1024.
Expected Behaviors:
(Under all situations, the instrument brightness rheostats should be preserved correctly.)
ATTR_cockpit + 2-d panel:
- The 3-d cockpit should look exactly like the 2-d cockpit.
- The 2-d panel is used as source.
- Panel transparency is preserved.
- Spot/flood lighting effects are available and work.
- Flood color is the forward flood color.
- The panel texture and object texture may not look the same under some lighting conditions.
ATTR_cockpit + 3-d panel:
- The 3-d panel is used as source.
- Transparency is preserved.
- Spot lights are not available, but flood flights work.
- Flood color is the side flood color.
- The panel texture and object texture may not look the same under some lighting conditions.
ATTR_cockpit_region + 2-d panel:
- The 2-d panel is used as source.
- Transparency is not available.
- Spot and flood lights are not available.
- Panel and object texture colors should match under all lighting conditions.
ATTR_cockpit_region + 3-d panel:
- The 3-d panel is used as source.
- Transparency is not available.
- Spot and flood lights are not available.
- Panel and object texture colors should match under all lighting conditions.
The Future
Basically both the 3-d panel and ATTR_cockpit_region are aimed at next-generation cockpits – they both strip legacy features to provide a clean platform for real 3-d cockpits. The expectation is:
- Global lighting will be applied to all 3-d geometry – panel texture and object texture. Non-emissive lighting (spot lights, flood lights) will apply to everything.
- Windows will be built using geometry, not alpha.
- The panel texture can be minimized by packing a 3-d panel and using regions. Manipulators let you provide interaction to regular object geometry.
With X-Plane 9.20 you can stretch the shape of generic instruments, to create instruments that appear to be in perspective. But why does this effect apply only to the overlays and not the burned-in backgrounds? Two reasons:
- Some planes are made by cutting out photographs of real cockpits. So the source imagery may already be distorted. The current feature distorts only the moving parts that have to be dynamically distorted, but lets you use pre-distorted imagery from a photo.
- Our distortion might not be as nice as what can be done with high-end image editors like PhotoShop. By pre-distorting the image you can get the best image quality.
And of course, the implicit reason 3 is that I’m lazy. 😉
Posted in Panels
by
Ben Supnik |
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.)
ATTR_cockpit_region
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.
Keyframes
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.
Manipulators
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.).
There are a few cases where you cannot use DDS files in X-Plane:
- Airplane 2-d panels (any layer – base, lit, -1 shadow layer, 2-d or 3-d).
- Airplane instrument images.
- Bitmap-based region specification referenced in a library.txt file.
- 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!
If you create plugins, airplanes, or scenery for X-Plane and haven’t tried your add-ons with X-Plane, please do so soon!! It’s much easier for us to fix backward-compatibility problems while we’re still in beta. Beta 14 introduced some bugs (that should be fixed in beta 15 real soon) but I think we’re reaching the point where you can do compatibility testing.
We’re working on a public Linux beta – see here.
