An author asked me some questions that I think are so important that I’ll blog the answers:
- The new texture paging system (LOAD_CENTER) works for both terrain textures (.ter files) and draped polygons (.pol files). You do not have to use draped polygons to get texture paging – you can use paging in a base mesh!
- Orthophoto terrain via a (.ter) file is by far the preferred method for orthophoto sceneries – it is a vastly better option than draped polygons. Draped polygons are horribly wasteful of hardware resources, and should really only be used for tiny areas, e.g. airport surface areas. If you are using even a moderate amount of orthophotos, make a base mesh!
- MeshTool is the future of photo scenery, and will continue to be the way to make high performance orthophoto meshes for X-Plane.
The future of MeshTool is bug fixes, a richer syntax, and some day maybe a UI front-end.
I just received a series of reports today that certain converted scenery will cause X-Plane to crash with a “bad alloc” error. Basically, this couldn’t have hit us at a worse time. The final 920 was cut a week ago. We physically can’t recut; Austin is on the road, and I am knee deep in it. But there is a possible work-around, and there will be a patch. Here’s the whole situation.
What is a Bad Alloc?
A bad alloc error is an error that comes up when X-Plane runs out of memory. This can happen for two reasons:
- We have run out of address space – that is, there is no more virtual memory left, or
- We have run out of page file/physical memory – that is, we can’t back that virtual memory.
The first case is by far the most common – you’d only hit the second if you are on Windows with a fixed-size (but small) page file. (Hint: if you have a fixed size page file, make it big!)
X-Plane can run out of memory for many reasons – everything that runs in the sim uses memory, and the amount used depends on what area you are in, what rendering settings you pick, and what third party add-ons you use. While I’d like to someday reach a point when the sim tells you gracefully that it’s out of memory, it will always be a fact of life that at some point (hopefully an absurdly high one) the amount of stuff you’ve asked X-Plane to do will exceed how much memory you have.
(If you are thinking 64 bits, well, that will just change the problem from a crash to a grinding halt when we run out of physical memory.)
We see bad allocs when there are too many third party add-ons installed (XSquawkBox is a particular pig because it loads every CSL on startup), too complex scenery, and it can also be caused by drivers not efficiently using memory. (This is particularly a problem on Vista RTM.)
The Bug
When X-Plane creates a curved airport taxiway, it allocates a temporary memory buffer to hold the intermediate product of the pavement. The size of that buffer depends on the complexity of the curve it is processing and a constant, based on the maximum curve smoothness.
In 920 I provided an option to crank up the curve smoothness in X-Plane. In the process, I increased that constant factor by 4x, which causes X-Plane to hit its memory ceiling on layouts that used to be acceptable. You’ll see this problem more often on:
- Bigger, more complex layouts.
- Configurations that were already chewing up a lot of memory.
- Machines with less address space (Windows without /3GB, older Mac OS X operating systems.)
What really suckered us about this bug was that it comes in a form that looks almost the same as a driver issue we’ve seen with ATI drivers on Windows — we’ve seen strange forms of memory exhaustion on ATI when shifting scenery with high rendering settings. So we didn’t realize that this was something new until G5 users reported the bug (making us realize it wasn’t a driver thing).
What To Do
The bad news is that we can’t do an RC5 – we’re out of time. But – there will be a patch – relatively soon. This bug is on the short list for a patch to fix 920.
In the meantime, there is actually a work-around. By coincidence, some of the internal rendering engine constants are viewable via the “private dataref” system — basically a series of datarefs in the sim/private/… domain that I use for on-the-fly debugging. The dataref that matters here is:
sim/private/airport/recurse_depth
If you load up DataRef Editor you’ll see it has a value of 12 . That’s too high. Changing it to 10 will allow otherwise problematic airports to load.
I will try to post a plugin in the next 10 days that sets this dataref to 10 on startup, effectively patching the problem. This will also limit the maximum smoothness of curves – but my guess is that if you see the crash (not all users do) then you can’t run on the max airport curve setting anyway.
Of course the next patch will contain a real solution: a more efficient memory allocation scheme!
Some users reported during 920 beta that X-Plane would sometimes not detect its DVD – a condition that would come and go. Tonight I figured out what is happening.
- In order to validate the DVD, X-Plane decompresses part of its contents into the preferences folder. Why preferences? There is no good reason – it’s historic.
- X-Plane will create a preferences folder if there is not one. But it does not do that until you quit.
- The X-Plane installer will not make directories unless they contain files.
So put these three things together: on the first run of a new install, there is no preferences file, so the DVD check fails since the directory that will contain some temporary files is missing. Run a second time, and the directory is there and the DVD check succeeds.
The next patch of the sim will fix this, but in the meantime, if you delete your preferences, leave the empty directory in place!
Two random and unrelated notes:
First, RC4 is going out as is, despite the engine modeling changes being incomplete. Basically we now have a more sane approach to the engines themselves, but no FADEC control. FADECs are on the short list for the next update. Sometimes we just run out of time – not every release can have everything.
Second, a note on autopilot customization – I am party to a fair number of questions about whether the plugin system can be used to make subtle changes to the autopilot logic. The answer is of course: no. If you really want something different for an autopilot, you’d have to replace the entire “top-half” set of logic and drive the flight directors yourself – in this situation you are responsible for:
- All modes and mode changes based on conditions.
- The actual selected flight envelope to achieve the desired AP setting.
But you are not responsible for driving the trim and yoke, which are done by you setting the flight director.
Why can’t you just override one specific behavior? It’s an issue of infrastructure.
Fundamentally, the autopilot only does a few certain tricks. If it were capable of doing customized behaviors, you’d already see it, in the form of a dataref or (more likely) a Plane-Maker setting. Basically there is no generality to the autopilot that we secretly have inside the code but don’t expose.
Will there be a more general autopilot someday? Maybe – I don’t know, I don’t work on that code. But the plugin system has always aimed to make it possible to do anything, but not necessarily easy. In particular, the plugin system doesn’t aim to make your development easier by recycling the simulator itself as a convenient library of lego bricks. In the end of the day, X-Plane is an application, not a library. If it were a library, that would be lots of fun for third parties, but it is not.
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.
I don’t like to delete/reject people’s comments, but I do not want new users to find this blog, see tech support requests, and add their own, only to have them sit unanswered for, well, ever.
If you bought X-Plane from Laminar Research, the tech support contact info can be found here:
http://www.x-plane.com/contact.html
If you bought X-Plane in a store, the distributor will have their own tech support contact info on the box.
From this point on, I am going to reject requests for tech support that come in the comment box. If you need help with X-Plane, use the email or phone number found on the contact page above!
Posted in News
by
Ben Supnik |
I believe I am getting close to a possible solution for the dreaded “Framebuffer Incomplete” errors – these error messages pop up when X-Plane starts, and you end up quitting.
If you meet these criteria, please contact me:
- You have an ATI card that has shown this error in the past.
- You can put on the latest Catalyst drivers. (I know a lot of you have put on older drivers to work around this.)
- You can run X-Plane 920 RC2.
If you’re in this crew, please email me at my XSquawkBox email address!
The rub is: despite having four machines with ATI cards, I never see this error. So I need to send you a build to get close to a fix!!! Let’s swat this bug for real!
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 |
My last post generated number of posts from both sides of the “hardware divide” (that’d be the have’s and have-not’s). I think everyone at least grasps that developer time is finite and features have to get prioritized at the cost of other features, even if not everyone agrees about what we should be coding.
I think the term “hardware divide” is the right one, because the hardware market has changed. Years ago when I bought myself a nice shiny new Dell (back when that wasn’t an idiotic idea) a medium-priced Dell had medium-priced hardware. Not only did I get a decently fast CPU (for the time), but I got a decent AGP bus, decent motherboard, etc. The machine wasn’t top-end, but it scaled.
When you look at any computer market, you need to consider what happens when consumers can no longer accept “more” and instead want “the same for cheaper”. This change in economics turns an industry on its head, and there are always winners and losers. (I have
claimed in the past that operating systems have turned that corner from “we want more” to “we want cheaper”, a shift that is very good for Linux and very bad for Microsoft.)
Desktop computers hit this point a while ago, and the result is that a typical non-gamer computer contains parts picked from the lower end of the current hardware menu. You’re more likely to see:
- Integrated graphics/graphics by the chipset-vendor.
- System memory used for VRAM.
- Slower bus speeds, or no graphics bus.
- GPU picked from the lowest end (with the fewest number of shader units).
- CPUs with less cache (this matters).
Someone commented a few days ago that computers would get more and more cores, and therefore multi-core scalability would be very important to fully utilizing a machine. I agree.
But: how many cores are those low-end PCs, aimed for general use (read: email, the web, text editing) going to have?
My guess is: not that many. Probably 2-4 at most.
These low end PCs are driven by one thing: price – the absence of VRAM or dedicated graphics hardware is all about bringing the hardware costs down – a $25 savings matters! In that situation, box-builders will want the cheapest CPU, and the cheapest CPUs will be the physically smallest ones, allowing for more chips on a wafer. A low-end PC will get no benefit from more than 4 cores – the intended use probably doesn’t even use one.*
Multiple cores are great because they give us a new way to benefit from smaller transistors (that is, by packing more cores on a chip, rather than clocking it faster, which has real limitations). But I think you’ll start to see the same kinds of gaps in CPU count that you see now with GPUs.
(In fact, the mechanics are very similar. The main differences between high-end and low-end GPUs of the same family are the number of parallel pixel pipelines – the low-end chip is often a high-end chip with a few defective pipelines disabled. Thus you can have a 4x or 8x performance difference due to parallel processing between siblings in a GPU family. Perhaps we’ll see the same idea with multi-core chips: build an 8-core chip, and if 4 of the cores fail, cut them out with the laser and sell it as a low-end chip.)
* One advantage of multiple cores is that they can take the place of dedicated hardware. For example, there is no penalty for doing CPU-based audio mixing (rather than having a DSP chip on the sound card) if the mixing happens on a second core. Being able to replace a dedicated component with a percentage of a core is a win in getting total hardware cost down, particularly if you were going to have the second core already.
With X-Plane 920 RC1, the user can now control how smooth taxiway curves look. More smoothing looks better, but can slow frame-rate.
Below are four pictures of KSBD (which has good, sparse vertices) at the four rendering settings.
