X-Plane 9 introduces a new OBJ feature: panel regions. The basic idea is this:
In X-Plane 8 you could use the 2-d panel as a texture in your 3-d cockpit. This allows a plane to have a moving map or glass display in the 3-d cockpit. However, the panel texture is expensive, particularly in v9 for a few reasons:
- You have to take the entire panel, even if you don’t use it all. For example, consider all of the “wasted space” from the windows.
- The real texture is rounded up to a power of 2 (and in x-plane 9 that could mean 2048×2048 for a a 1600×1600 panel.
- The texture has an alpha channel, which probably isn’t usfeul (model your 3-d cockpit windows in 3-d, not using transparency). The alpha channel increases VRAM use by 33% and requires some pixel shader gymnastic in v9 that slow things down.
- In X-Plane 9 this is all twice as painful since we have a panel day and and lit texture.
Panel regions address all of these problems. Here’s how they work:
- A panel region is a rectangle within your 2-d panel. It can be placed in any location as long as it is (1) fully within the 2-d panel and (2) its dimensions are a power of 2.
- The cockpit object declares up to four panel regions it wants to use.
- A new attribute lets you use each of the four panel regions as a texture (alpha is not provided – the regions act opaque).
This does exactly what you might expect: it creates between one and four smaller power of 2 textures rather than one huge one and manages those smaller textures. We do have more textures, which is usually bad but we get some big wins:
- Better VRAM use. The panel texture, being a dynamic texture, puts a lot more pressure on VRAM than regular scenery textures. Without this optimization, we could be paying 25 MB of permanent VRAM use just for the 3-d cockpit. Now we don’t have to pay to round up to a power of 2.
- Faster updates of the 2-d panel into the 3-d texture, since we have to process a lot fewer pixels.
- Efficiency – a clever author can cut down the panel use to only the parts that really matter, which might only be the EFIS at 256×256 pixels.
I will try to provide detailed documentation on this in the near future. There will be a new ac3d plugin coming out (hopefully in the next week) that will provide both editing capabilities for key frames and for panel regions.
We still haven’t fixed the crash bug in X-Plane 9 yet, but we have narrowed it down to:
- Windows only
- nVidia only
- Pixel shaders only
We actually know partly what happens, but we don’t know why, and we don’t know how to fix it yet (short of disabling VBOs or pixel shaders, both of which are unacceptable workarounds). Austin’s shipped b4 with shaders off, just to get people running while we work on this.
So I went to BestBuy last night and bought a 6200 (out of desparation) – I can now see the crash bug for myself. My framerates are also terrible. My guess is I can tweak the drivers, but having experience now with the 5200, 6200 and 7300, I can safely say: avoid the lowest end nVidia cards. In particular:
//en.wikipedia.org/wiki/Comparison_of_NVIDIA_Graphics_Processing_Units
The important thing to look at here is “core config” (although bus width and clock speeds will always be higher in the higher end models). For the last four generations, nvidia has made three levels of cards: a hig end card (with a number like x700, x800 or x900), a mid-range card (usually x600) and a low end card (x200, x300). So for the GeForce 6 series, the 6800 was the flagship card, the 6600 was the mid-range card and the 6200 is the “budget” card.
Each time they go down a level, the number of shaders and other parallel hardware resources gets cut down. This translates directly into lower framerate, particularly in X-Plane 9 where we’re shader-bound when you use the shader features. I often recommend the mid-range cards as a good value, but the low end cards aren’t worth it – they’re too stripped down for not much price savings.
Back in the good old days (that would be X-Plane 6), X-Plane’s framerate would suffer in two ways as you cranked up the rendering options:
- For most features (more visibility, more autogen) as the CPU and GPU became more heavily loaded, the framerate would gradually decrease.
- If you ran out of VRAM (that is, the working set of textures needed per frame was more than your card’s VRAM) framerate would really die fast – think 2 fps.
The reason for this second behavior was that computers couldn’t shuffle textures between main memory and VRAM fast enough to render a frame in a 30th of a second.
As computers have gotten faster, this second behavior has gone away – modern cards, with fast PCIe 16x busses, can transfer textures from system memory to VRAM pretty fast – fast enough to have the working set be (slightly) larger than VRAM and still fly. So as texture memory increases, framerate decreases more gradually.
However, a new behavior has emerged: “glitching”. You may have noticed that when you’ve got your computer set to the ragged edge of the rendering settings, as you turn the camera, the framerate will stutter for a few frames, then return to a relatively high rate (40-50 fps).
What’s happening is: the working set of textures and geometry needed by X-Plane just barely fit in VRAM. But when you turn your head, a different set of textures and geometry are needed. While the card sorts out what is needed and what isn’t, it spends some time needlessly shuffling textures, and eventually reaches stability, with only what’s needed in VRAM, and framerate stays high.
Glitching has emerged as a mode of performance degredation because over time we’ve cut down the amount of “stuff” (textures and geometry) x-plane needs to draw a frame to only what’s really absolutely needed. This means there is less intersection between the working set in one view and another, and it also means you can get closer to the edge of your hardware.
So my view on glitching is basically “too bad”. If the working set weren’t as carefully trimmed, you wouldn’t have glitches, but the framerate would be entirely low, not entirely high. The only solution is to turn down settings that increase the working set (object density, world LOD, tex res, forests…) until the computer can run without glitches.
An even stranger variant of this: users sometimes report framerate getting “stuck” at 19 fps and then coming back when they change apps. The problem is that the driver doesn’t know exactly what the best order of textures to keep in VRAM vs. shuffle is…as the view changes, sometimes the driver ends up with a non-optimal decision about what stays in VRAM and what goes, causing framerate to drop. Changing which app is in the foreground fixes this by temporarily pushing a lot of items out of VRAM, at which point the driver makes a different decision by luck.
Again, the solution is simple: turn down rendering settings to get the working set smaller than VRAM.
Basically, if the working set is smaller than your amount of VRAM, you should have even framerates, proportional to rendering load.
If the working set is greater than VRAM, the driver may find an optimal way to shuffle things and only decrease fps a little, or it may find a non-optimal way to shuffle and you’ll get terrible fps, and that shuffle can change on the fly, causing framerate to fluctuate all over the place.
In X-Plane 9 betas 2, you can use the livery system to provide alternate textures for misc objects attached to your plane, but not the cockpit objects. Beta 3 will address this, allowing cockpit objects to reference the livery system too. We’ll get some examples posted for how this all works soon.
Austin and I were discussing this last night – here’s a few thoughts on the difference between the misc. objects and the cockpit object:
- Because you can have multiple misc. objects, you can effectively use more than one texture for your airplane. These days plane designers want a lot more than one texture.
- We’re working on optimizations for attached objects – basically by breaking your plane carefully into a few objects, you may be able to optimize frame-rate. A lot of this code is not in the sim yet, but will go into a later beta.
- Using multiple objects with different LODs is a much more efficient way to improve fps than simply having multiple LODs of the entire plane.
For example, make an interior object with a low LOD (0-500 meters) and an interior texture. Attach it. Then make an exterior object with an exterior texture and a longer LOD (0-50000 meters). When you back away from the plane, X-Plane can entirely skip the interior object, which means that neither the geometry nor texture have to be moved to VRAM. That’s a big performance win.
The cockpit object is also different:
- The cockpit object induces the sim to make a texture out of the 2-d panel. (And it is the only object where the panel texture is legal.)
- Mouse-click analysis is only done on the cockpit object. If you load up the cockpit object with all of the animation for your landing gear, X-Plane has to wade through all of that animation to update the mouse cursor in the 3-d cockpit.
- The cockpit object can be swapped for an alternate object in the exterior view (we’ll provide more control of this for misc objects soon).
So my general advice is: use the cockpit object only for the real panel itself!
However, we have provided livery support. You can’t livery the 2-d panel, and the livery system is not meant to reskin cockpits, but there are probably some planes out there that used the cockpit objet to model exterior plane features (from before we had misc objects). The livery system in beta 4 will let you reskin these planes without changing how your obects work.
One trend I’m seeing in the forums is a wide range of reports on X-Plane 9 framerate. I see both “X-Plane 9 runs faster than 8” and “it’s so slow I can’t fly at all.”
In my experience this kind of situation is often due to hardware-specific performance issues…that is, X-Plane is doing something that is fast on one kind of GPU but slow on another. Once we figure out what the problematic operation is, we can replace it with something that’s fast for everyone.
If you’ve got all of the eye candy turned off, everything on minimal, and are still getting 20 fps, that’s not X-Plane 9 being a pig, that’s something wrong with X-Plane 9 on your particular system. Please…try beta 3 when it comes out, then if it’s still slow, report a detailed performance bug and we’ll investigate.
X-Plane 9 is currently in beta 2. Long-time X-Plane users know that a lot of bugs get fixed between early and late betas, and they also know that a good number of bugs get added between the early betas.*
If all goes well, X-Plane 9 beta 3 will be out in a few days. My advice is: don’t panic. X-Plane beta 2 crashes for a number of users, so our top priority is to fix the crash and get the fix out ASAP. If your bug doesn’t get fixed in beta 3, it’s probably because we’re still working on it but didn’t want to delay getting the crash fix to users.
Similarly, beta 3 will include some performance improvements, but more are coming. Beta 3 doesn’t represent the end of our performance tuning, it represents the first beta that we can do serious analysis with. We only have a fraction of all of the supported video cards within the company, so if your computer is having performance problems, well, we’ll figure out what’s going on in beta 3 and then fix it.
* Our approach to bug fixing is: if a piece of code is buggy because it’s subsystem has a design problem, we go in and fix the design problem, even if we’re in beta. Other companies might say “no fixing design problems (which changes more code) during beta.” But the way I look at it, badly designed code is just going to cause problems all the time until it’s fixed, and it has to be fixed some day, so why wait.
(Why would there be badly designed code in X-Plane, or any computer program? Computer programs change over time, and the functionality they perform changes and grows. As this happens, the designs of the past no longer make sense for future requirements. In my experience most design problems come from code “outgrowing” its framework.
So our approach is to upgrade the framework as soon as it shows signs of growing pains, rather than jamming as many features into the existing framework as possible until it becomes so overcrowded that we can’t get anything done.)
To answer some speculation and questions I’ve seen on the forums regarding X-Plane and multiple cores:
- X-Plane 8 and 9 will use up to four cores to “shift” the scenery coordinate system when scenery needs loading. This shift causes a pause in both X-Plane 8 and 9, but it is a relatively short pause.
- X-Plane 8 and 9 will use a second core to build 3-d geometry out of road, forest, facade, and airport definition data while you fly, as you move through the loaded scenery area. This is particularly important to smooth flight when there is a lot of 3-d enabled.
- X-Plane 8 and 9 will use a second core to do some of the work of loading textures from disk while you fly. (Right after a scenery shift happens, over time new textures are loaded in.) Some of that texture load is still done on the main thread. Texture compression is done on the main thread, which can cause stuttering. (I expect to address this in the future, but authors can use DDS textures now in v9 to simply not do the compression at all and make everything faster.)
- X-Plane 9 will load new DSFs into memory on a second core. Loading new DSFs takes the vast majority of scenery load time, thus flight with X-Plane 9 and a dual-core machine is a lot smoother than it was in v8. This is a big win for the dual-core machine and is new to v9.
All of our new work on the sim keeps multi-core in mind. We know that more and more users will have multiple cores and that we’re leaving performance on the table if we can’t distribute rendering load across two cores.
So the important points here I think are:
- X-Plane 9 significantly uses a second core.
- Use of the second core has grown significantly over time, and will increase in the future.
- I like to use bullet points way too much in my blogs and emails.
When someone posts bad performance with X-Plane 900b2 vs. 864, the urge for me to respond is overwhelming. I spend a lot of time very carefully comparing old and new versions in controlled situations to make sure we haven’t let any part of the engine get slower.
For now I will try to hold off – there are a few basic things we can do with beta 3 that will change not only the performance of the sim, but also how the rendering settings are organized.
For now a few immediate thoughts:
- If you are looking at a new graphics card, don’t plan your hardware purchases on the beta. Wait for a final build to evaluate.
- There is no free lunch – settings that don’t exist in v9 (volumetric fog, reflective water, forests) are going to cause lower fps than 864. (You could set the forest setting to “insane” in v864 with no penalty, as long as you had no forest add-ons installed.)
And finally, something I find myself saying over and over and over: there is no relationship between the fastest computer on the market today and the highest settings in X-Plane. We do not guarantee that the fastest computers can run x-plane “maxed out”.
The highest rendering settings represent the most detailed output our engine can make, and the most data we have (based on what fits on the DVDs). We provide this very high rendering setting because:
- A user might want a lot of detail in one area and not others. You can run on “insane” roads if you leave the other settings dialed down, or reflective water can be on if you don’t have a lot of objects or world LOD. So even if having ALL settings on maximum kills virtually any computer made today, having some settings on maximum can be useful.
- If you buy X-Plane 9 now you are entitled to every patch (and then you may use it long after the version run is over). So you might be using X-Plane 9 for 2, 3, or 4 years. Settings that are impossible to reach on today’s hardware may be very usable on future computers.
So we do not penalize users who want some settings very high, or future users, by preventing you from setting the settings in any way you wish.
Please understand that the settings are not calibrated the same as X-Plane 8. If you set the rendering screen to look “as close” to x-plane 8 as possible, you are almost definitely not getting the same amount of detail (and the same load on hardware) as you were in 864. They are not comparable. Trust what you see out the window while flying, not what’s on the rendering settings screen.
I’m sure I blogged this before, but the blog’s gotten old enough that I can’t find my old posts. This came up in an internal company discussion, so let me say it again:
ANIM_hide is not a framerate optimization. 99% of the time it doesn’t make your object draw faster.
ANIM_hide is provided to let authors make certain animated effects (like swapping out a prop disc for blades based on prop RPM). These are animated effects and cost fps, because they use the CPU and interrupt the graphics cards from just blasting out triangles at warp speed. An example:
You might have a very complex object attached to a plane that doesn’t need to be drawn at all, like a landing gear assembly. This object could have its own texture, a ton of animations, and high triangle count. Using a giant ANIM_hide around it to prevent drawing when the gear is retracted does you no good. Here’s why it doesn’t help.
- Before an object can be drawn, X-Plane prepares the geometry and texture to be used by the card. These are atomic operations (we have to prepare the whole texture and all of the geometry no matter what we will actually use) and they are expensive.*
- X-Plane then must evaluate the animation command on the CPU to decide if the object must be drawn. If the object drawing is simple and the object is drawn, this CPU work is just wasted, so this technique wouldn’t even make sense unless the object is hidden a lot of the time.
- If the object is hidden, X-Plane will still run through every command in the object, simply skipping drawing. So if the object is heavily animated, we still pay a lot of CPU for the “hidden” object.
You will actually save some performance with ATTR_hide in one situation: if the geometry that is not drawn with ATTR_hide covers a huge amount of the screen (e.g you are really close to the object) then not drawing the pixels saves frame-rate. This would be extremely unlikely – you’d have to hide an entire cockpit from the inside to see any kind of benefit with this.
Why doesn’t ANIM_hide actually skip work? Well, it may someday, but for now it’s a question of how we optimize objects. When we load objects, we evaluate their command sequence and attempt to consolidate and remove unnecessary CPU work. We remove unnecessary state change, combine drawing commands when possible, etc. This works because we know at object-load time exactly how the object will be drawn. But consider this bit of OBJ “code”:
ATTR_flat
ANIM_begin
ANIM_hide
ATTR_smooth
TRIS 0 30
ANIM_end
TRIS 30 60
ATTR_smooth
TRIS 90 120
If ANIM_hide really skipped work, is the ATTR_smooth routine necessary? Can the last two TRIS commands be combined into one big TRIS command? If ANIM_hide removes an attribute, we don’t know until we actually draw the object what attributes will be run. But if we say ANIM_hide doesn’t affect state change (which requires us to actually do the state change) we can then realize that none of the state change in this object are actually necessary, saving 3 attributes, and allowing us to combine a triangle batch.
So for now our policy is one of simplicity:
- ANIM_hide is for artistic purposes, but not optimization purposes. It simply stops drawing, it doesn’t eliminate work.
- The optimizer then goes to work on your object.
- I think we will someday provide a new mechanism for the “landing gear case”, one that’s specifically designed to quickly eliminate parts of a plane that are expensive and don’t need to be drawn.
* X-Plane does try to optimize out this cost in some cases. For the purpose of drawing, an object can get “culled” (not drawn at all) by being too far away for LOD or fully off-screen, or it can get “drawn” (meaning we do look inside the commands). Culling is very very fast, and drawing is usually quite slow. The optimization of avoiding using geometry and textures always work in the culling case, but usually do not work in the drawing case. So having a smart LOD on the landing gear is a huge win.
I don’t actually know all of the best ways to make an apt.dat file. The format is new and we haven’t had a ton of time to performance test it. But here are some thoughts:
- One thing I know is…it is best to describe the shape you are using with the fewest number of nodes possible. In other words, let bezier curves do their thing, don’t add a ton of vertices to them. And please don’t add vertices to try to make the curves smoother. The best thing is to leave the layout simple and let X-Plane render it. In the future we will allow the user to set the level of smoothness based on his or her hardware. Adding more nodes will hurt quality – we will be able to pick better nodes at runtime than you can in the apt.dat file.
- Avoid overlapping large areas of pavement. Overlap is bad – it hurts framerate by requiring the graphics card to draw the same pixels over and over. As X-Plane supports more advanced shaders for nicer lighting, this cost will be a lot heavier on users.
- Ignoring overlap, the question of whether to have several smaller chunks of pavement vs. one large one is a difficult question. I would suggest moderation – try not to make too many individual pavement elements, but don’t make the entire element one giant pavement either. You may have to experiment to find the best framerate.
