With regards to the scenery system, the idea of orthogonality is this: each part of the scenery system should be unaffected by other parts, such that they can be used together in any combination. This allows you the most options in creating scenery for a given set of features.
One way we try to achieve this is by only having one way to implement any particular feature. For example, because it is possible to place custom objects in overlay DSFs, we are unlikely to allow custom objects to be placed via the apt.dat file. Having two ways to place custom objects would invariably lead to subtle differences in how the two worked; not all features would be usable everywhere. It would also mean more code (read: longer time before you get to use the feature) and more subtle bugs.
Once we have a feature only available in one form, we can try to use that mechanism everywhere. For example, objects can be animated. Because any object can be animated and objects are used both for cockpits and scenery, the work we did to provide animation allows for animation in both scenery and the cockpit. When we get cars back on the road, they’ll probably be objects; navaids are also objects now, and someday hopefully ships and oil platforms will be too. Each time we recycle OBJ8 for a part of the system, animation becomes possible in a new domain.
So usually the ‘orthogonality’ strategy, code something once and use it everywhere with no duplication, means more flexibility and features being usable over a wider area. Every now and then though it bites us in the ass. Flexibility is a strength and weakness; the more we allow any part of the scenery system to work with any other part, the more likely two parts will be used together in a way that we never expected, potentially revealing bugs.
Here’s an example that I only realized existed today, after talking to Peter about animation: it turns out that if you use a textured light inside an animated object, the light (which is secretly a flat square that always points at the camera) will actually turn with the object, revealing that it is flat, and being invisible most of the time (either because it’s facing sideways and is very thin, or because it’s facing in the other direction entirely).
The problem is: when working on animation, I forgot about the textured light system and forgot to cope with the case where they interact. When the code is truly separate, an orthoganal design works well; where the code has internal interactions, it does not.
Do you care? Well, we are looking at some new features for the textured lighting system in 850; there is probably going to be some fine print about how you can use the new textured lights with animation. Even though the features are orthogonal, the code that runs it is interdependent, so some cases may not work right without extra work. How many strange cases we fix, and how many we say “just don’t do that” for will depend on how useful they really are. For example, not being able to have lights on animated objects at all would be a real limit, but perhaps not every kind of light needs to be usable within an animation. For example, VASI lights are usually just mounted on the ground.
I’m back, but things will probably be quiet a bit. A lot of new scenery features will be going into 850, but it may be a while before 850 is ready for test due to how much is going in. I’ll post more as I know it – my work for 850 will be mostly focused around improving the look of airport areas.
I’ll be out of the office for the next eight days; please be patient with bug reports and scenery questions. An X-Plane RC should come out soon and we’ll let it sit a bit to see how it does. I think we got the fog bug fixed!
In version 840 I tried to fix a persistent bug in X-Plane where objects sometimes randomly disappear…turns out I got the math wrong.
The next 840 beta (which I think will be called “RC1”, but I am a poor predictor of these things) has a bug fix to the bug fix. I don’t know how many of these bugs this will fix (some appear to be due to driver issues) but I think we’ll be closer.
I try to avoid politics in this blog, but this article that Jonathan Harris posted to the scenery list is pretty topical to X-Plane.
http://education.guardian.co.uk/universityguide2006/story/0,,1726985,00.html
Of course I am biased – low-cost high quality data (SRTM, Tiger, etc.) make it possible for a small company like X-Plane to create high quality scenery. But I would also add two more thoughts:
1. Knowledge is crucial to the healthy functioning of a democracy. Without good digital maps, you can’t apply modern tools to understanding regional trends, environmental problems, electoral districts, etc. Knowledge shouldn’t just be for the rich (or big companies).
2. Geospatial data is infrastructure – free or cheap GIS data make a country a better place to do business. I think in this global economy every national government needs to be asking “what are we doing to make sure our citizens will be competitive on a global level.” There’s no question that having good roads and transportation infrastructure are important for a national economy, but I would submit that having good digital infrastructure will become important too; in that context it’s appropriate for a government to make the data free (and take the local loss in the providing agency) to foster growth, employment, and the well-being of its citizens.
Just my 0.02…
Long time no post – it’s been a busy few weeks, helping friends with projects and traveling. There have been some lively discussions on the scenery list though!
I’ve been tossing around the idea for a fundamental change in the way the apt.dat format handles metadata. It’s subtle but I think it has some far-reaching implications.
Right now the apt.dat format is pretty high level. Let’s use taxiways as an example: a taxiway has a light code that indicates whether the taxiway has blue edge lights. This has two effects:
1. The information about whether the taxiway has lights is preserved.
2. You can’t put blue edge lights down without a taxiway.
I am exploring the idea of entirely separating edge-lights/lines* from taxiways. This would mean that:
1. We’d have no idea about whether the taxiway has lights. There may happen to be lights nearby, but we can’t be sure of where they come from and
2. We can put lights anywhere.
The shift is fundamental because it is reducing the amount of high level data and increasing file size in return for gaining flexibility with a simple system.
Anyway, email me if you have thoughts on this…food for thought.
* The exception will be runways. We will be supporting all existing data in the apt.dat format – nothing’s geting dropped, and there isn’t a real replacement for runways. Generally runways will still be built by saying “this is a runway and these are it’s many properties” and letting the sim do the rest.
X-Plane 8.40b2 introduces the ability to attach multiple objects to the aircraft. This is a very powerful new feature.
Currently these objects are not part of th physics model. This may change during the beta, or not. Please do not attempt to do real work based on the beta – an X-Plane beta is a test version of the sim and may change radically due to bugs we discover. Until X-Plane is final please try features and report bugs, but do not assume the features will continue to work the same way.
A few authors have asked me why the lighting looks different for the parts of a 3-d cockpit that use the panel. Here’s what’s going on:
The 2-d panel has 3-part lighting: the base background is lit by the ambient light levels with no regard to lighting angles. (Since the panel is 2-d we’re not really in a position to light different parts of the panel differentially.) The panel is then additionally lit by the cockpit flood lighting and any instrument gauges are further lit by the instrument brightness, for example an EFIS.
The 3-d panel is then built by taking an image of the entire 2-d panel. Here’s where things get tricky. The image of the 2-d panel has already been darkened by the ambient lighting levels and brightened by the flood lights.
If we were then to apply directional 3-d lighting (the way we do for normal lighting) we would further dim the panel (which would make it too dark) and we would dim the EFIS and other instruments.
But since we don’t apply directional lighting, the panel texture does not match teh surrounding non-panel geometry in a 3-d cockpit.
There are a few possible things we can do about this:
1. We can leave things the way they are and require 3-d panels to carefully use the clickable parts only for small areas to minimize the visual impact of the lighting effects.
2. We can build the 3-d panel separately out of multiple textures. This would allow us to do truly correct 3-d lighting, but would have some pretty big performance implications. The 2-d panel would have to be rendered multiple times, and the total VRAM requirements would increase by several megabytes. Since the panel is never compressed or resolution-reduced, VRAM is a serious consideration.
3. We could disable all 3-d lighting for the 3-d cockpit. This would cause all geometry to match, but give the 3-d cockpit a flat look. Authors would have to build their 3-d lighting into their texture.
None of these options is ideal.
There have been a few cases where we’ve dismissed a feature request as “impossible” – only to then implement it later. There are a few reasons why this happens:
- Sometimes we’re just wrong…we didn’t understand an algorithm or know of a technology. Later research gives us a clue.
- Sometimes the underlying technology we use changes, either OpenGL and the operating system. (The joystick bundle was totally necessary for X-Plane through 832 since it was a CFM application – 840 is Mach-O, allowing us to run bundleless for the first time.)
- Sometimes we have to make changes in our own code. A feature that is near impossible in one version could be one line of code in the next. This is because so much of our features depend on underlying systems. We spend a lot of our time working on the underlying systems to make multiple features possible at once.
So please do not be surprised when the impossible becomes the possible; one of the things that makes flight simulation and enjoyable problem to work on is that new technology constantly unlocks new possibilities and lets us make each version of the sim better than the last in ways that would have been impossible.
It’s winter and I seem to have caught another case of Emailus Overloadus, also known as a clogged in-box. If you emailed me in 2005 and haven’t heard back, please ping me again. If you’ve emailed me in the last six weeks, I apologize for the extended delays; I am trying to get to everyone in the next week or so. Sadly email seems to come in faster than I can answer it.
