Category: Development

Vulkan and Metal: Testing and Bug Fighting

Last week we sent out our first build of the Vulkan/Metal ready X-Plane (which will be version 11.50) to an external sight, and last night we sent out the first private beta.

Our plan is to move to an open public beta soon once we have some feedback on how well the build is working. When that is will depend on the bug reports; I’m crossing my fingers.

How It Works

In X-Plane 11.50, there is a check-box in the rendering settings that enables Vulkan or Metal; you’ll have to restart for the change to take effect. If the sim crashes really early (e.g. before the main menu) it will revert to OpenGL to keep you from getting “locked out” but random crashes while flying won’t do this. There are also command line overrides to control the driver for people running performance testing scenarios.

I should also mention that we’ve changed what the reflections slider does – it’s now like X-Plane 10 and does not attempt to update the environment cubemaps in real-time. (If you really like flying at 5 fps, you can re-enable this in settings.txt – the underlying tech has not been removed.)

What we have found over the last few years is that users will drag every slider all the way to the right, and then be surprised that the sim has poor performance. While I have in the past dismissively claimed that they are doing it wrong (“don’t put every topping on your pizza”) the inevitable truth is that we are violating an industry UI norm by having the highest possible settings run beyond the scope of the fastest possible computers our users can get their hands on.

Now that we have Vulkan and Metal running, we can make some judgments about what will and won’t be real-time. Full scenery shadows are still available and are helped by the Vulkan and Metal driver; a decent machine should be able to run full autogen + scenery shadows at 30 fps.

The Vulkan and Metal back-ends change their approach to running out of VRAM. With the OpenGL driver, when VRAM is exhausted, textures are moved to system memory, and the application stutters while the driver makes this mad last-minute shuffle.

When running with Metal and Vulkan, X-Plane will reduce the resolution of your textures while you fly, in the background, without stutters, preferring to reduce resolution on textures that are not being used right now. The result should be smoother and generally less disruptive. You can still lower the overall texture resolution to better fit your card’s budget.

This new “on the fly paging” is…well, it’s completely new, and I suspect it will need a lot of debugging during beta. It’s an area where we just need to collect use-case data to better tune the algorithm.

X-Plane 11.50 no longer allows for uncompressed textures – if a DDS is present on disk, we will use it. I have to recommend texture compression in the strongest possible terms; while the artifacts are annoying, when we turn it off, everything looks worse due to the VRAM pressure – uncompressed just isn’t a good way to use our VRAM budget. Pre-compress your textures for best results!

A Detailed View

One of the great things about running with the Vulkan/Metal back-end is that there isn’t any dark matter in the rendering path – everything that takes time takes that time when we say so. This means that when we have a stutter we can take the frame apart and figure out exactly why that happens.

One of the last fire-drills before sending out a build happened last week – with the Vulkan back-end and memory paging working correctly, we would still see these violent stutters flying over downtown LA. As it turned out, the code to delete autogen as you flew away from it was too slow and was causing hitching every time a 3 km AG square had to be torn down.

That code is now rewritten and the results are much smoother. Here’s what winning looks like:

This is my old iMac running at 60 fps – it can’t do that with everything maxed out, but when it does hit 60 fps you’ll note the dead even orange bar at the top – that’s consistent framerate. The bottom of the screen shows a block diagram of some of the tasks that went into the current frame render.

With “weird driver behavior” removed, when something stutters, so far we’ve been able to identify it, e.g. the autogen stutters from last week. Here’s what stutters look like:

The orange spikes you see are the stutters – I induced these by command-tabbing to other apps while flying; when the window manager swaps apps it’s pretty disruptive. That big blank space in the middle of the screen is time spent doing something (probably in the window manager) that we do not yet track.

One last show-and-tell pic: for some reason when running at 45 fps, the sim is actually running at a mix of 60 and 30 fps every other frame, which is not good. We can easily see this with our tools:

Here we can see two frames, a long one on the left and a short one on the right. The difference: “acquire surface” is taking a ton of time. The long frame is stuck waiting for the window manager to give us some VRAM to draw into. With this kind of detail, we can at least understand the bug and try to fix it.

Next Steps

At this point the only thing left to do is fix bugs, some of which are still open even as the private beta goes out. We will move to public beta once we have something where we think the initial experience isn’t a blue screen and tears.

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End Caps for Line Files

Here’s a feature that went into X-Plane 11.35 that will be really exciting to a very small number of scenery authors: in X-Plane 11.35, line files (.lin) can have custom painted end-caps on each end, and the texture repeats can be aligned to a grid.

Scenery authors who have gotten deep into X-Plane’s scenery system will already know from that first paragraph why this is useful, but for normal people who have seen the sun in the last 30 days, .lin files are the art files that define the look of thin linear features. X-Plane uses them for the painted yellow and white lines in the airport environment, but a developer can use them for anything linear.

Line files repeat, tile, and can follow the ground in a bezier curved path, which makes them great for curved taxiway lines. Their achilles heal up to now has been that when the line ends, the line just … stops. This makes them inappropriate for really thick uses, where that hard “cut” at the end of the line would be really noticeable and ugly.

In X-Plane 11.35 you can provide a start and end cap for each line definition. Like the line itself, it can be mulit-layered if desired. So, for example, you could use it to make dirt paths between buildings in a rural airport – where the path ends you can have a “soft” ending to the path and not have to worry about tucking the line under another scenery element to hide the cut.

We’re not using these in the default art yet, but the code is done, and I have updated the .lin file format specification with the new syntax.

Posted in Development, Scenery by | 3 Comments

Add-on Developers: Please Try X-Plane 11.35 Beta 4

X-Plane 11.35 beta 4 is now live – run our updater and check “get betas”. Release notes here.

Steam users: we’ll release this tomorrow if there isn’t a sign of a huge fire overnight – it’s already uploaded to the servers.

Add-on Developers: if you haven’t run your add-on in 11.35, please put it through its paces now. Everything that might be risky or weird is already in and we’re just killing off bugs now. If your add-on has a compatibility problem, we need to know now if we’re going to fix the problem during beta. While we’ve tried to make everything “just work” with old add-ons, there’s always the chance that your add-on does something special we didn’t think of. Please test now!

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FlightSimExpo 2019 Talk

Here’s our keynote talk from FlightSimExpo 2019 last week!

FSExpo 2019

Evans video team really did a fantastic job with the feed this year – everything was live-streamed in great quality, and the talk has a direct feed to the slides and good quality audio. Totally what we were hoping for!

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WED 2.1 Beta

You can now grab the WED 2.1 beta here. This is a minor update with bug fixes and enhancements such as extending the facade preview to all types of facades and to the map window. You can also read Michael’s extended release notes here.

New Meta-tag Identifies 2D or 3D Airports

We’d like to point your attention especially to the new “2D” or “3D” meta-tag for export targets of 11.30 or higher. This tag tells the X-Plane GUI to list the airport as “2D” or “3D”.

Before X-Plane 11.35, the information in the “Features” column in the X-Plane airport selection menu came from any scenery in a user’s Custom Scenery directory, rather than being an entry in the system-wide apt.dat in the Resources/default scenery/default apt dat/ directory. The assumption was any addon airport would always be 3D. But starting with X-Plane 11.33, all global airports, even those with 2D-only layouts, were now included
in the Global Airports –which made the X-Plane GUI effectively list every airport as “3D”.

At export, WED 2.1 will analyze the scenery for 3D content and look for the existence of the meta-tag “GUI label”. If the export target is 11.30 or higher it will warn if the tag is missing or improperly set, ultimately leaving it up to the designer how they want the airport to be listed in X-Plane. If the target is “Gateway”, it will forcibly create or update this meta-tag to always be set correctly according to the actual scenery exported.

In order to fix the 2D/3D display in X-Plane 11.35 and later for any scenery not submitted via the Gateway, authors will need to manually add the tag via “Airport->Add Meta Data” and then re-exported to a target of X-Plane 11.30 or higher.

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Vulkan and Metal: It Runs!

Since my last Vulkan update, we now have the full sim running natively with Vulkan and Metal! There is still a pretty big list of random things turned off or bypassed to make this happen, but we can fly in the cockpit and use the sim.

Here’s some stuff that is now working:

  • Using regular and HDR rendering, and SSAO on metal.
  • Flying with Vulkan on AMD, NVidia, and Intel drivers.
  • Hardware stereo rendering on OS X – this never existed before Metal because the Mac GL drivers didn’t support it. Hardware stereo rendering is necessary for VR support.
  • MSAA on Metal – with the restructuring of our code, you’ll be able to change MSAA settings without restarting. I don’t know if this code works on Vulkan right now; it might.

Here’s some stuff that does not work yet:

  • Plugins are bypassed right now. We have not yet written the plugin-OpenGL-interop layer.
  • VR only works when using OpenGL as the driver; we need to write some new VR code to pass Metal and Vulkan frames directly to the OVR and Rift APIs.
  • Screenshots/Movie capture are a work in progress – that’s what I’ve been working on this week.

We still have a number of visual bugs, so screenshots are an important feature so we can run our automated test system. The test system takes hundreds of screenshots of the sim in many configurations and compares them to 11.30 to catch bugs introduced by the new Vulkan and Metal back-ends. Clearly I’ll have to fix my color problems first.

One fun aspect of this port: Metal and Vulkan copy Direct3D’s convention where the viewport Y axis points down and not up. This resulted in a whole series of weird “it’s upside-down again” bugs, most of which have been fixed.

The world is drawn correctly but the atmosphere around it is upside down.

(That airplane might look silly, but at least all of the image is consistently upside down. That’s because the only remaining upside down code is the movie/screenshot capture code itself.)

We should have some performance numbers to post next week; right now our primary focus is fixing bugs, particularly bugs that bring the whole machine down.

Here are a few more pics of things that have gone wrong during development.

Posted in Blooper Reel, Development by | 71 Comments

X-Plane 11.33b1 Out Now

X-Plane 11.33b1 is an incremental update that includes updated Gateway airports and translations, crash fixes and diagnostics, minor UI improvements, and bug fixes such as:

  • XPD-9441 Weight, balance and fuel- Total weight (lbs) does not include weapons.
  • XPD-9683 Fix dupe banks in FMOD crashing the sim.
  • XPD-9882 Fixed KOAK nav data.
  • XPD-9919 Lightning appears in cockpit in VR.
  • XPD-9991 Crashes on older Intel GPUs.
  • XPD-9992 Default FMC, Holding Pattern will only be flown once.
  • XPD-10003 Landing lights has no effect on battery amperage draw.
  • XPD-10007 Fixed slip ball limit.

For a full list of bug fixes, see the release notes here.

Just a reminder that the sim will not prompt you to install this beta–you will need to launch the installer manually and opt into betas to get this version.

We are putting more effort into cleaning up frequent crashes. We recently upgraded our back end crash reporting to a fancy paid service that we hope will allow us to gain a lot more insight into what is going wrong. This beta includes additional crash logging for that purpose.

Keeping in the crash-fixing vein, we believe we also fixed two notable crashes in this beta: issues with Intel GPUs and with duplicate FMOD sound banks. We heard from a lot of Intel users about these crashes, so Sidney took a look and was able to find a fix for it. The FMOD crash has been a round for a while and was caused by duplicating an aircraft folder that included FMOD. When an FMOD bank had the same contents on disk at a different file path, FMOD wouldn’t load it. We now handle this case gracefully.

Update: Steam users can get 11.33b1 by selecting the public beta under application properties.

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Vulkan and Metal – a Quick Status Update

Just a quick update on our progress with Vulkan and Metal. We last spoke about this on the live feed a few weeks ago, but we’re a little further along. Here’s the summary:

  • Plane-Maker and Airfoil Maker run in Vulkan and Metal.
  • X-Plane runs in Vulkan and Metal up to the main menu (e.g. the app starts) but can’t yet fly or show scenery.
  • The Vulkan and Metal code runs on Mac, Windows and Linux.
  • The Vulkan code runs on Nvidia, AMD and Intel drivers.
  • All shaders are ported.
  • All of the zoo animals (abstractions around part of the graphics engine) are now complete. We killed off the last 2 or 3 since the live feed.

For the last two weeks, Sidney and I have been working to port all rendering passes to the new code, so we don’t have to go through OpenGL to fly the aircraft. I lost a few days dealing with this:

That turned out to be a single if statement that got reversed deep in the mesh drawing code during one of the porting steps, resulting in some of the runway lights being replaced with random pieces of … heck, I never figured out what the wrong mesh was, just that it came from some other unrelated part of the sim and changed as the camera moved. To make matters worse, the error only appeared on the Mac, so we couldn’t use Windows OpenGL debugging tools to find the issue.

The silver lining is that once we are all Vulkan/Metal, we’ll have at least four separate debugging tools to go after bugs like this.

We don’t have measurements of performance yet; once we can sit in an aircraft in X-Plane running Metal or Vulkan, we can at least get some initial performance numbers.

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X-Plane 11.32

We’ve posted X-Plane 11.32 release candidate two – it contains very few changes from release candidate one. If you think RC2 changed your framerate from RC1 (for better or worse), it is imaginary.

The big item for RC2 is that X-Plane now uses our own replicating METAR servers. NOAA weather was plagued by 404s when the server posted METARs didn’t meet the date/time scheme X-Plane expected. Our own server should serve the latest weather we have, whatever that is.

Over the last few weeks we have spent a tremendous amount of developer time investigating reports of instability, crashes and performance problems, and the results have been quite unsatisfying. We really haven’t found a series of smoking guns we could fix to improve stability. We have learned some things about X-Plane’s performance and stability though. The rest of this post gets into the weeds; if you tune out (and I won’t fault you if you do) the TL;DR is: please turn on our anonymous analytics, and click “send” if you get the crash report form. The more gathered data we get about crashes, the better shot we have at addressing the issues.

Crash Rates and Plugins

X-Plane’s overall crash rate (all causes is approximately 14% – which is to say, for all of our users using analytics, for every 100 times they launch X-Plane, the sim quits in a way we did not expect or want 14 times. This number has been remarkably stable – it’s not a ton different between 11.26, 11.30, 11.31 or the 11.32 beta.

The sim quitting on purpose because of bad content is not considered a crash. For example, if you load a DSF with a missing .ter file, the sim will refuse to proceed and quit. This failure mode is user hostile in that you can’t fly, but it’s not a crash – the refusal to load is the code working according to design. While I would like to make this code less hostile to users, it’s also worth noting that these cases are ones where the author of the scenery pack would have been able to fix this if they had loaded their own work even just once. That is, they are caused by an add-on that should not have shipped.

(There is an in-between area where an add-on is mis-installed because it has a library dependency that the user hasn’t met. This is a deployment problem that really needs to be solved, but it’s orthogonal to true app crashes.)

We categorize crashes into plugin and non-plugin crashes; starting with 11.32 we actually get a statistical picture of this.  A crash is a plugin crash (and you see the “we crashed because of a plugin: XSquawkBox” or whatever) if the sim crashed while executing code on behalf of a plugin or inside the plugin on the main thread.

There are a bunch of cases where plugins do not get correctly tagged – in particular, we regularly see crashes on random worker threads spawned by plugins; since we don’t know whose thread it is, we can’t blame the plugin. For example, the FF A320 crashing inside CEF on a worker thread is registered as an X-Plane crash (and we see it in our auto-reporting view) but it’s not our code and there’s nothing we can do about it.

One thing I’d like to do in future patches is improve diagnostics. The rate of actual blamed plugin crashes appears so far to be quite low, and given that we do see uncaught plugin crashes in our data on a regular basis, I think this is a case where add-on authors can only fix what they can see. If we can attribute all plugin crashes to plugins, then the plugin authors can catch their own bugs. Better diagnostics also helps a user remove a troublesome add-on in the case where that would help.

“Known” Crashes

We have a few cases where X-Plane hits an error condition and deals with it by crashing. This is pretty bad, drives up our crash rate, and is something we need to fix to be less user hostile. For example, if a PNG file is bad (either corrupt contents or the sector on disk that backs it has gone bad) then X-Plane’s response is usually to mysteriously crash. Besides being rude, the crash gives an end user no idea which file is bad, and thus no way to fix it. X-Plane ships with something like 9000+ PNG files and over 2500 DDS files, not counting add-ons, so if we don’t tell you which file is bad, you’re not going to find it by poking around.

FMOD sound bank incompatibilities is another example – if you have two aircraft sharing a byte-wise copy of the same FMOD data (e.g. command-D duplicate the C172) loaded at once – then our FMOD loading code fails and then registers as a crash. The code is working exactly as we designed it, but the design isn’t robust enough. As we’ve learned, in the real world users duplicate aircraft (and their FMOD packs) on disk all the time.

The crashes in this category are things where we’re being user-unfriendly and better code would make these problems go away or leave users with a way to actually fix them. But they’re not case of “weird stuff inside the sim blew up.”

Persistent Stability Problems

In the crash data we do also see a few persistent stability problems. There’s some kind of crash in the ATC system that we’ve seen for a very long time but we don’t know how to reproduce. It’s a case where if enough users do enough random stuff, we hit an edge case in the ATC system that isn’t handled correctly. The solution here is to embed more diagnostics at the crash site until we can understand it from the reports we get from users. Please hit “send” when you crash – don’t worry about filling in the fields – it’s the report itself that we need.

We also see a lot of crashes inside the OpenGL drivers, from all of NVidia, AMD and Intel. Because the IHVs don’t share symbols and source code with us, we really can’t tell what went wrong in these cases.

My hope is that with Vulkan we’ll have better options for in-driver crashes. With Vulkan, they redesigned the error checking model: error checking is a feature you enable (via a configuration option at app startup) that brings a layer of code in on top of the driver to check what the app is doing. With error checking off we get the fastest framerate, and with error checking on we get slow framerate (more error checking means more slow) but some really great diagnostics.

(To put this in perspective: when Sidney ran the Vulkan version of Airfoil-Maker on Linux with the wrong driver installed and no error checking, it rebooted his entire Window server!  So no error checking really means: no error checking.)

Since error checking is optional and selectable when the app runs, we could put an option into X-Plane to run in “safe mode” – if a user is hitting persistent stability problems in the driver, that user could turn on validation and possibly capture an error in X-Plane itself that would otherwise just be “the driver crashed.”

Running Out of Memory

I’ve worked with a few users to try to track down the out of memory problems we’ve heard about, and there isn’t an obvious pattern here. Some users report running out of memory in 11.30, but when put back on 11.26, find that they still run out of memory. We get more out-of-GPU-memory complaints on 11.30, but that might be because a few cases in 11.26 that were crashes due to running out of memory now report the problem in an orderly way. In 11.26 they were just mysterious crashes with a “send” form.

In the cases we’ve seen, the user running out of memory was often…actually running out of memory – that is, the surprising thing is not the crash but that X-Plane ever worked at all on those settings. The fundamental problem we face is that we have no visibility into what the OpenGL driver is doing with GPU memory. The OpenGL tries to manage memory no matter how much we ask for, and if it fails, we don’t know what went wrong.

The good news is: we have much better options for Vulkan. With Vulkan, we manage memory, which means we know what’s going on, and we can take steps to avoid out of memory crashes. If we do run out of memory, it should be for much more obvious reasons. We’re still analyzing what we can do about memory with Metal, but the choices should still be better than OpenGL.

The only advice I can offer now if you are seeing persistent memory crashes is: turn your settings down or use less add-ons. If you push X-Plane to the limits of your hardware, it may work for a while and then fail.


Sidney has looked at a lot of performance data from users who reported low framerate, and in almost every case, the performance has been as-expected. The most common case we see is users with relatively low single-core CPU performance hitting low framerate at high rendering settings while their GPU is bored. To put some numbers on this, if your CPU’s single-core geekbench score is down around 2000, you are almost certainly CPU bound, way at the bottom of what’s okay for X-Plane, and a new GPU won’t help.

As of now, X-Plane cannot use large numbers of cores (e.g. a 32-core machine is useless) and gets only limited performance boosts for framerate with multiple cores under some circumstances. This is something we are working to change in the future, but it’s not going to change quickly. If you are looking to improve performance with hardware, single core speed is still the most important metric.*

In a few rare cases we saw performance that was disproportionately bad compared to what we’d expect from an old CPU. We’re trying to gather more data from these users but the case is rare enough that we haven’t gotten a useful report yet. If we find a smoking gun, we can act on it.

Like memory, Vulkan will help with diagnosing performance. With Vulkan, more of the code is written by us and the Vulkan code we run has very predictable timing. So when we get complaints about performance, we’ll be in a much better position to understand what is slow and why.

What’s Next

I’m actually not sure what the next patch will be, but we do have a bunch of bug fixes to 11.30 waiting to go out once we have stabilization under control. I also have a pile of bugs that I have not yet fixed that are high on my priority list where something in 11.26 stopped working in 11.30. So if you have filed a bug that’s not fixed, we have not forgotten about it – it’s either next to come out or possibly on the short list.

* Yes, we realize that this dependence on single core speed is bad. It’s just going to take time to move to Vulkan and then offload the single thread.

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Seaplane Testers Needed

We have received reports in the past about X-Plane 11’s seaplane dynamics when the aircraft is in the water.

If you would like to test sea plane water dynamics with an experimental build, please email Austin directly – he has some fixes for seaplane behavior and he is looking for early testing.

Update: fearless leader^H^H^H^H^H^H^H^H^H^HAustin says he is only looking for testers who have experience flying a real world small float plane with pontoons, so that he can get test feedback from someone who can validate the reality of the physics.

(You will need to install a custom build from him on top of X-Plane 11.31 to do this.)

Update 2: fearless leader^H^H^H^H^H^H^H^H^H^HAustin say he has enough testers. If you’re not getting builds now, you’ll have to wait for a public beta.

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