Category: Aircraft

Aircraft shadows and icons in 11.10

With 11.10 there is a new way aircraft only shadows are done, as well as how aircraft icons are generated. The big change is how we calculate the volume of the aircraft which up until now was based on all OBJ files that the aircraft ships with, including things like ground- and fuel trucks, stairs etc. The reason this is undesirable is because the greater the volume of the aircraft, the worse its realtime shadow quality will be because we use the volume of the aircraft to calculate our shadow map area. The bigger that area, the worse the shadow quality and the more pixelated it will look like. In an ideal world, the aircraft volume tightly hugs around the actual aircraft and we get the best shadow quality possible. With 11.10, hopefully this ideal world is finally here!

Why and how we failed before

Before 11.10 the aircraft volume was based on the volume of, well, the aircraft. However, this includes things such as the aforementioned ground trucks, fuel trucks and what have you, that artificially blow up the volume calculation. The problem is, all these objects are technically part of the aircraft (eg. we move them around with the aircraft), but they are for the most part invisible and most people wouldn’t actually consider them to be part of the aircraft proper.

In 11.05 we added a change to also consider the physical volume which kind of has the right size for the plane but doesn’t include OBJs. It is based on the physical size of the plane only, which sounds like it’s the right thing. However, as it turns out, this volume breaks badly for things such as helicopters because the rotor of some third party helicopters are attached OBJs and won’t be considered part of the physical volume of the helicopter.

At this point I should probably also quickly note what happens if the shadow volume is too small: Everything that gets clipped by the shadow volume will cast a shadow into infinity and beyond due to the way the shadow mapping works. This is especially bad for the helicopters that now have very quickly rotating bits that are constantly clipped by the shadow volume resulting in shadows flickering all over the place.

In short: What we want is a shadow volume that is as tight as possible around the aircraft for shadow quality, but not too tight because that also leads to problems.

What’s new in 11.10

In 11.10 the algorithm to compute the shadow volume has been completely changed. Instead of trying to jiggle around with the physical volume and the volume of all OBJs together and then coming up with a sane value, X-Plane now looks at what is actually being rendered. We start out with the physical bounding volume as before, but then we look at what is actually rendered! For that, we go through every OBJ that is marked as casting shadows and run the OBJ engine as if we were to render the whole thing. So OBJ animations as well as kill datarefs etc are considered. This happens during the first frame, so everything is set up the way it would be during normal rendering. Everything that is visible will be marked as such and the shadow volume will be expanded to include this OBJ.

The result is a volume with a tight fit around what is actually visible and therefore considered “aircraft”. Everything else is not included in the shadow volume and therefore stops casting shadows altogether. Of course, this is only in aircraft only shadow mode and is not used when scenery shadows are on. In that case, everything is handled like it was before and everything that is supposed to cast shadows does cast shadows. So, if you see missing shadows in aircraft only shadow mode, this is probably due to this change.

To visualize the differences, here are 4 screenshots showing the quality difference as well as the new shadow volume:

One thing that should be noted though is that going forwards these kinds of extra OBJs should really be done via the new drawing API in the 3.0 SDK! This allows us to very accurately determine the size of the aircraft but it also means that culling will become more accurate. The old method will of course continue to work, but it’s not the best or most efficient way to approach ground vehicles and other ground clutter.

Aircraft icons

The calculated volume for the whole aircraft with attached OBJs was also used for the aircraft icon generation. This led to some weird cases where the camera was positioned in such way that the aircraft was incredibly tiny due to the fact that we tried to get “everything” in at once. So far the recommendation was for authors to create a version of their aircraft without all the extra OBJs attached, but now that we have an adequate measure of the aircraft volume this is fixed as well! Aircraft icons should be correctly generated now with the camera positioned to capture the plane at the right distance.

There is one more fix for aircraft icons: Some authors created aircraft that did some clever culling based on where the pilots head is and then using the kill dataref to prevent parts of the aircraft from being rendered. Reading the view dataref now correctly reports the camera as being an external camera so that those custom culling solutions work with the aircraft icon generator. If your aircraft still doesn’t generate proper icons after 11.10, please file a bug report and let us know!

Improving AI Aircraft

AI planes face two major issues in X-Plane 11:

1. AI aircraft are often way more resource-intensive than they need to be. Users are fine paying a performance penalty to load, say, a super detailed 3-D cockpit model for their own aircraft, but for AI planes, where you’re never going to be in the cockpit, there’s no reason for that sort of thing. A significantly “dumbed down” version of the same aircraft would allow users to load more AI planes at once, with no visible downsides during normal use.
2. Many aircraft, for one reason or another, simply won’t function at all when used as AI planes. This is most commonly due to one of two issues:
   • reliance on third-party plugins (which only work for the user’s plane)
   • lack of support from X-Plane for flying aircraft like this (for instance, the X-Plane AI doesn’t know how to fly gliders, seaplanes, or rockets)

As a user, this is really frustrating, because it’s difficult or impossible to know in advance which aircraft will work as AI planes and which will either a) just sit on the runway, never able to take off, and/or b) tank your frame rate.

Coming in X-Plane 11.10: AI-Only and User-Only Aircraft

In the upcoming X-Plane 11.10 beta, we’ve added two new options to Plane Maker’s Author window: “supports user flight” and “supports AI flight.” By default, all aircraft support user flight, and do not support use as AI aircraft.

If a plane is configured for AI flight only, it will never be shown in the normal aircraft grid—only in the AI aircraft window.

If a plane is configured for user-flight only (or if it’s a pre–11.10 aircraft with no “supported flight type” info), it will be hidden in the AI aircraft window by default, but for the sake of backward compatibility with old planes, users will still be able to reveal them by checking a box labeled “Show aircraft without AI support.”

The upshot for aircraft authors

In the Glorious Future, we envision third parties shipping two versions of their aircraft:

• one marked user only, which include all the bells and whistles, plugin-enhancements, and as much detail as possible
• one marked AI only, which is stripped down for performance, only using plugin enhancements that have been tested in AI configurations.

The result will be a faster, more consistent, less error prone experience for users.