Simon and Chip have a whole series of posts reviewing the plane, with lots of nice pictures.
Simon and Chip have a whole series of posts reviewing the plane, with lots of nice pictures.
X-Plane 9 allows you to categorize objects as being on the plane’s outside, inside, or glass. X-Plane depends on these flags being right for a few things:
It is important that you use these flags as intended; X-Plane 10 depends on this information as well, and X-Plane 10’s global spill and global shadowing algorithms are more sensitive to incorrect categorization of objects than X-Plane 9’s forward renderer.
In particular, you should have glass for the airplane windows in an attached object tagged as type ‘glass’; do not attach your glass to the cockpit object, which cannot be categorized as glass. If you have an old plane with glass in the cockpit, consider cutting the object in half in a 3-d editor and attaching the glass separately.
(You should also use our prop disc animation, rather than use an OBJ for prop discs; the OBJ format doesn’t contain the z-buffer tricks necessary to make the prop look right.)
For quite a while now, I have been advocating in favor of DDS compression. I am pretty damned obstinate, but eventually if enough people yell at me, I get a clue. I have come to appreciate that there are some cases where DDS compression is not a net win; this blog post explains when it happens and what we might do in X-Plane 10 to work around this.
DDS – The Good, The Bad, the Ugly
DDS is a file format that contains image data pre-mipmapped (that is, the smaller versions of the image that the video driver needs are included) in a format that may or may not be compressed. DDS is virtually always used with a compressed image format (like DXT1 or DXT5). This has three positive effects for X-Plane:
The bad is that the DDS file does not contain the original uncompressed file. If the user unchecks “compress textures to save VRAM”, DDS files remain compressed. If the image file contains details that don’t compress well, they’re going to get splatted and stay splatted.
What If VRAM Grew On Trees?
My original heavy arguments for DDS were based on the idea that VRAM is a limited commodity; if we don’t compress textures, the user runs out of VRAM faster and has to go down a level of resolution…and once that happens, everything starts to look ugly.
But what if the user has 1 GB of VRAM? At this point, we’ve limited the maximum quality the user can see because we don’t have the original uncompressed image anymore, only the DDS/DXT version. This can be frustrating to authors who spent a lot of time on their textures.
If you ship PNGs with your airplane or scenery, turning off texture compression will reveal this beautiful, uncompressed image, but now when texture compression is on, the compression will be done by the video driver, and that will look extra ugly.
The Best Of Both Worlds
This is my thinking for version 10. (These are just musings, we haven’t coded this yet.) Currently DDS are preferred to PNG files. We could relax the load rules in version 10 to prefer PNG over DDS when texture compression is off and DDS over PNG when it is on. This would allow authors to ship both PNGs and DDS files and have the right one be picked for the scenario: the pre-compressed one when texture compression is on and the uncompressed one when compression is off.
Quick airplane links:
Pictures available in both links.
I realized I have slightly better test shots of global illumination than the ones that got out a week ago. These are from only a day or two after the last shots.
This is the Cirrus again, with landing lights and strobes; you can see that all of the airplane’s lights contribute dynamically to the lighting on the fuselage and doors as they move. (Yes, that is heat blur on the engine; the heat blur still needs a lot of tuning.)
This shows airplane-mounted lights interacting with custom scenery. In this case the standard Cirrus (with global lights attached) casts both strobe and multiple landing light spill on LOWI. One of the powerful results of global illumination is that we get correct lighting interaction between diverse content, including third party content.
Finally, this shows an airport beacon lighting a plane and vice versa. The global lights on the airport beacon are inside an animation group, making them “sweep” the airplane, which can in turn animate the airport beacon. With global illumination, there are no rules about who lights who.
Thanks to my foolish use of unprotected directories, we have basically announced that X-Plane 10 will feature global illumination. Here is some basic information on global illumination.
What Is Global Illumination?
Global illumination is the ability of any part of an airplane or scenery system to cast light on any other part of the scenery system or airplane. In X-Plane 9, the only lights in the sim that ever actually cast cast light anywhere else are:
This list was kept short due to the high cost per pixel of each light on all rendering.
When X-Plane 10’s global illumination is enabled, a “spill” light attached to any OBJ can shine light on anything near it. Since any OBJ can have a spill light, this means we can have light sources on airplanes, scenery, cars, whatever you want. The spill effects any 3-d scenery nearby, even from another scenery pack.
This kind of still effect can be simulated in X-Plane 9 by careful use of LIT textures. However, real global illumination works between art assets created by separate authors. You can drive your custom airplane up to a custom airport and the landing and logo lights on the airplane will cast light on the terminal; the apron lights from the terminal will cast light on the airplane.
Furthermore, global illumination is fully dynamic – as objects animate or move, the lighting effects are correctly applied in 3-d. This makes effects possible that cannot easily be created using LIT textures.
Requirements for Global Illumination
Like most new rendering tricks in version 10, global illumination will be a rendering option that can be optionally enabled by users who have a video card meeting hardware requirements. In the case of global illumination, that requirement is a DirectX-10 generation video card, e.g. any Radeon HD , nVidia GeForce 8000 or 9000 series, and “100” series (100,200,300,400 series).
For authors: global illumination is applied using named and parametrized lights on your OBJ. Anywhere you can attach a light billboard, you can attach a spill effect as well, with some tuning constants for how wide you want the light, etc.
It will be possible to create two versions of your LIT textures, one to be used when global illumination is enabled, and one when it is disabled. Thus if you are baking lighting into your textures with a 3-d modeling program, you can simply re-bake the lit texture with some lights disabled and add 3-d lights to your model. The result is an airplane with real 3-d lighting where possible, and a close approximation via baking otherwise.
Global illumination can be added to a model incrementally; existing art content will work normally with global illumination enabled or disabled, so authors can choose to add a few light spill effects or add a large number, as time permits.
The Cost of Global Illumination
Global illumination isn’t going to be free. The main cost is an increase in VRAM use and fill-rate. The cost of global illumination is mostly a one-time cost to put X-Plane into a new rendering mode. (Graphics nerds: global illumination is implemented via deferred rendering.) The incremental cost of lights isn’t that high, although a scene with a lot of lights will have impact.
My expectation is that users with new, highly capable high-end graphics cards will be able to run global illumination easily, but will lose some of the other benefits of fill rate. (For example, running at 2560 x 1024 + 4x FSAA is a lot more painful with global illumination than without.)
Global illumination also introduces two artifacts, both of which I am trying to minimize as best as I can. These artifacts are a function of deferred rendering – all games that use deferred rendering have to address these problems:
(Hardware-based FSAA can make a number of optimizations like CSAA to optimize throughput; this is how such high multiples as 16x are possible. Since our implementation is similar to “super sampling” and costs a real 4x in performance, 4x will be the highest setting.)
Why Global Illumination
Of the new X-Plane 10 rendering engine features (and there are a fair number of them), global illumination is certainly the one that has the most impact on the structure of the rendering engine. With global illumination, X-Plane effectively has two separate modes (“forward” rendering, which is the only mode X-Plane 9 has, and “deferred” rendering, which produces global illumination).
One of the reasons to get global illumination done earlier than other features was that implementing global illumination required rewriting or modifying nearly every piece of low level rendering code. Now that the work is in place, we can safely add new features and test them in both modes.
Global illumination also meets two requirements:
Sergio has long observed the central importance of lighting and shadows in the look of X-Plane; at some point more polygons and better textures still look synthetic without a realistic illumination model. Global illumination makes a more realistic lighting model possible at night. Airports represent an environment that can hopefully take advantage of such capabilities in a big way.
As hardware becomes more powerful, authors have to do more work to create content that takes full advantage of the rendering engine. We are reaching a point where artist’s time is going to be a limiting factor as well as hardware and engine capabilities. Global illumination thus kills two birds with one stone: it makes the rendering engine’s output look better, but it also makes the whole scene look better with less work by the artist.
(For example, when baking lighting into a model, the author must plan the model’s texture UV map to guarantee unique texture space for all spill effects. When lighting effects are dynamic, the author can simply texture so the model looks good without worrying about baking requirements.)
A month ago the blog was quiet because there was a lot I couldn’t talk about; now it’s quiet because I am up to my eyeballs in X-Plane 10. I’ll try to get out a few posts I’ve been meaning to write, but it’s definitely crunch time.
I have received a number of emails from plugin developers who wanted to know if they could modify some of the sim/aircraft datarefs, or why modifying them had no effect/an unintended effect.
The short answer is this: in some cases X-Plane will pre-process and cache data that comes from the .acf file. In this case, a sim/aircraft dataref (most of these come from the .acf file) can be read, but writing it will have no effect because the sim has already had its one look at the dataref.
This is a design limitation; it was never the intention of the SDK to allow complete Plane-Maker-level editing of the aircraft on the fly in the sim.
There were a few threads regarding lighting rheostats in X-Plane 9. Here’s a short version of the issue and why we’re not changing X-Plane 9’s behavior.
X-Plane 9’s policy toward lighting rheostats is a little bit arbitrary. The sim will pre-position every lighting rheostat in the cockpit to 75% intensity on sim startup, and from that point on, we never touch them. We do not reset them when you load a new plane or reset your flight.
The result of this is that when you load a new airplane, it “inherits” the rheostat positions of the last airplane loaded. This can cause a problem if the newly loaded plane doesn’t have controls to adjust the lights (e.g. it has no instruments on the 2-d panel or manipulators on the 3-d panel, and there is no keyboard shortcut defined). A plane can be “stuck dark”.
It would be nice if X-Plane would pre-initialize the lighting rheostats on startup, but X-Plane deos not have enough information to do this. For example, on plane load, the instrument brightness should be set fairly high (so a glass cockpit can be read during the day) but the flood lights should be fairly low (to prevent loss of night vision). But X-Plane has no idea which rheostats control instruments and which control floods. So if we wanted to correctly initialize the cockpit, we wouldn’t have enough information.
To make it more complicated, some airplane authors have taken it upon themselves to initialize the cockpit via plugin code. If X-Plane were to start changing the rheostats at startup, it might undo some of what these plugins have done.
Given the difficulty of maintaining compatibility and the lack of a “correct” set of values, we decided not to change the behavior in 9.50 or 9.55.
If there’s any take-away point for airplane authors, I think it is this: provide controls for the lighting rheostats that you use in your airplane. Otherwise the user can’t turn the lights on if they are off for any reason. You can control the lighting rheostats with a generic instrument, manipulator, or the built-in instruments.
There is a separate issue that sometimes comes up: X-Plane panels can look bad when the flood lights are turned all the way up during the day. A panel can look very red and washed out, for example.
This problem comes from a mismatch of real-world lighting levels. In the real world, the sun is approximately four gajillion times more powerful than the little dome lights in an airplane. So when the sun is out, the dome light isn’t visible even if it’s turned all the way up. The dome light only looks bright when your eyes have adjusted to a no-sun condition.
What X-Plane should do (and may do in the future) is scale all cockpit lights relative to the overall daytime brightness, which would effectively dim the effect of flood lights during the day. Simply turning down flood lights when a flight is started during the day is not a full solution, as the user can simply turn them right back up again and end up with an unrealistic scene.
Suffice it to say, I think we will address these things in a v10 time frame, not a v9 time frame; in the short term it’s better to have airplanes continue to function as the author intended.
I was discussing plugin-controlled prop discs with a third party developer. The developer wanted to know if custom prop disc control would end up inside Plane-Maker. It may end up doing so, but I don’t think this would be nearly as useful as it would seem. What follows is my explanation to him of why this is.
Let me draw an analogy: when it comes to systems modeling, using a plugin is to Plane-Maker as using Blender is to using Plane-Maker.
Users who cannot use Blender are frustrated because they cannot make something as nice as those who are building planes out of OBJs. Sometimes they ask for more features in Plane-Maker, like: more stations! This new editing mode! Make the UI better!
But…you tell me: will Plane-Maker’s UI ever be as flexible and powerful as Blender? And if it ever did get to be that good, would that have turned out to be a good use of LR’s time, when Blender is already available?
The motivation for OBJ-based airplane geometry via third party tools is that what users want to do cannot be easily generalized into a few simple cases. Every plane is different, so a truly flexible platform is needed.
The prop disc (and other systems modeling problems) are the same way. In developing the prop disc graphics, I spoke with a number of third party developers who had already tried to push prop discs as far as they could go, were using plugins, were drawing themselves, as well as 25 other crazy hacks. I also spoke to our internal art team. And what I found was: no one had any consensus on how the prop disc system should work. Everyone wanted to tune a very specific set of behaviors to their peculiar art assets.
That’s what drove me to put it into a plugin. When we need an equation or a strategy we reach the point where we need more flexibility than Plane-Maker can exhibit. A plugin can encapsulate a strategy or technique in a way that Plane-Maker radio buttons cannot.
Consider what would happen if custom prop disc parameters were built into Plane-Maker. Everyone would have to wait until Austin implemented the prop disc algorithm they wanted. How would this be bad? Let me count the ways?
This problem is already happening across pretty much every aspect of systems modeling: airplane have unique, quirky systems which are usually useful for exactly one plane. It is not even remotely sustainable for X-Plane to code these things one at a time with a set of check-boxes. We might as well have a pop-up menu for every airplane ever invented, and simulate every single airplane inside the sim itself. Imagine the development costs…if a single high quality MSFS add-on sells for $30-$50…
Think of the prop disc via plugins situation (and the strobe lights are the same way) as an experiment in generic instruments for systems. By transitioning to a generic abstaction for instruments we’ve let a lot more users do exactly what they want with a small, high performance piece of code. The original instrument strategy (one of everything) reached a point where we simply couldn’t meet user needs in a cost-effective manner.