I sometimes get questions from authors considering how much to rely on a 2-d panel mapped to 3-d via the panel texture vs. a true 3-d panel. I can’t comment on what will look best, but I can comment on the relative performance characteristics of both techniques, and the answer might surprise you: in some cases you’ll get better performance by modeling directly in 3-d.
The 2-D Way
When you use the panel texture to make an object, X-Plane goes through a lot of steps to create the final result:
- Your panel has to be rendered in 2-d. We atlas your panel textures, but we don’t necessarily order them optimally – we don’t know the optimal order. Each generic instrument is at least one batch, perhaps even two. Those batches have very low vertex count, and the vertices are stored non-optimally on the CPU. There may be a fair number of texture changes between instruments.
- If you use ATTR_cockpit_region, we then go back and do the same thing…again! Why? Well, we need your panel’s raw color (“albedo” to graphics nerds) and the emissive light given off by anything self-lit separately, so that we can do correct 3-d lighting.
- Both of these are rendered to an off-screen texture that the video driver will feeel obligated to preserve at all costs, putting pressure on VRAM.
- Only when all that is done do we begin drawing your object, with the usual batches to change to panel texture and change back, perform animations, etc.
If this seems expensive, that’s because it is. Periodically users send me airplanes to look at their performance, and lately I’ve been seeing a lot more problems with 2-d panels (that fuel 3-d cockpits) being the performance bottleneck, not the 3-d modeling itself.
The 3-d Way
What if we want to go 3-d? Well, we’re going to “eat” a lot more of what your 3-d pit already has:
- You’ll need a lot more animations to move all of those parts.
- You’ll need new batches with ATTR_lit_level to dial up and down various lighting levels.
But you do get some advantages:
- Geometry in objects is processed about as optimally as we possibly can. All of that work we’ve done on the rendering engine to make OBJs fast is available in your cockpit. So you can increase 3-d detail ‘for free’.
- Your lit geometry can be drawn in a single pass (we don’t need to prepare two separate lit textures). So for example a needle would take three batches via the panel-texture route (a batch to rotate the needle for albedo, a second batch to draw the rotated night needle, and a third batch to draw the resulting texture in 3-d) but only one if you use the OBJ directly.
- Since you organize your textures for OBJs, you can guarantee that all of the cockpit stuff is together, saving texture thrash.
- You can use normal maps to add per pixel detail to your cockpit; panel textured geometry cannot be normal mapped.
A Balancing Act
Given the high cost of panel texture relative to native OBJ drawing, you’d think going native OBJ would be a no-brainer, right? Well, not quite.
A needle is an easy case: you can model a needle using a rotation animation, so your implementation in an OBJ and our generic instrument are quite similar. Same with the throttle lever generic instrument.
But what about a “glass pie indicator”? What about a moving map? What about a rotary?
There are some generic instruments that have “movement” for which there is no equivalent OBJ technique. With these generics, the generic instrument/panel code may be able to render the generic quite a bit more directly than your OBJ can simulate the same effect.
This is my suggestion on a cut-off: if you can directly model a generic instrument with an OBJ (needles, throttles, and other “simple moving things”), consider 3-d. If you would have to use a lot of extra texture space, copies of your mesh, or a lot of show-hides, use the panel texture.
Your goal should not be to eliminate the use of panel texture. But if you can cut panel texture down to a single 1024 x 1024 region from a larger area, you’ll probably see a performance win or a reduction in your airplane’s system requirements.
Performance Test First
Final thought: before you invest months in a complex cockpit design, mock up the “work-load” X-Plane must do and performance test it! For an OBJ, simply make one moving instrument and duplicate the mesh to get the number of expected animations. For the panel, drag out a bunch of instruments, make custom textures and just paint junk into them with photoshop. The goal is to make X-Plane do the same amount of work as it will in the final version. Then fly your test panel on target computers and observe performance.
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.
In order to understand the difference between hiding geometry and disabling drawing, you need to understand that an OBJ triangle can serve many purposes. Broadly, those purposes are:
- Drawing (the most basic use).
- Collision detection, of which we have three flavors: collision of the plane with the object (“hard surfaces”, or “physics”), collision of the mouse with the panel (manipulators, or clickable triangles) and collisions of the camera with the airplane (“solid camera”, which constrains the camera).
Any given triangle can be drawn and/or used to check for any of these collisions*; attributes change what the triangle is used for.
By default, all triangles are drawn; ATTR_draw_disable marks future triangles as not being drawn. This allows you to make a triangle that is used only for collisions. Examples might include a “hot spot” in front of a region on the panel (the hot spot might be easier to click than a small switch) and an invisible simple mesh to constrain the camera.
By comparison, ANIM_hide effectively removes some triangles from your model (temporarily) for all uses – drawing and collision detection of any kind. If a door is hidden, it’s not only not drawn, but it’s not going to stop the camera moving through it either.
Some key points to these distinctions:
- Categorizing what a triangle is used for (drawing, various flavors of collisions) is static – that is, it is always the same for the object and never changes with datarefs or animation. This is intentional for performance reasons!
- Animation to hide triangles affects the triangle in every way consistently – drawing and collisions.
Generally, you will get better performance improvements by removing categories from a triangle than by hiding it. (That is, it is better to not have manipulators on your cockpit, so it isn’t mouse-click collision-checked, than to hide it.) But the purpose of ATTR_draw_disable and ANIM_hide are different enough that which you use will be determined by the effect you are trying to create.
Finally, note that hiding an object completely (that is, the object does no drawing) does not provide the maximum performance benefit of not having an object at all. ANIM_hide was created to allow authors to create clever effects, not as a performance enhancer!
* This is not quite accurate: airplane-object collision checks are only available in scenery objects, and camera/airplane or mouse/panel collision checks are only available in the cockpit object.
Tom has a new video on youtube of his just finished Falco. The video shows what screen-shots cannot: that the mouse interactions on the plane are really well crafted.
If you’re just discovering X-Plane (or just discovering that X-Plane’s 3-d cockpits can be very interactive), here’s X-Plane’s “raw” capabilities for manipulation:
- The simplest manipulations are based on mapping the mouse from the 3-d cockpit back to the 2-d panel. This can only be done when the 3-d cockpit is textured using a piece of 2-d panel. This is the oldest way to make a clickable cockpit in X-Plane, dating back to the original X-Plane 3-d cockpits. The advantage of this method is that it’s very easy to set up; the disadvantage is that the mouse click gestures tend to be “flat” in their operation.
- As Tom’s plane demonstrates, you can manipulate just about any dataref or command via a drag along a specific axis. Axes are subject to animation, so there’s a lot of potential for “grabbing” things with this interface.
- X-Plane also supports direct “click” manipulation – this can be handy for buttons where you don’t want to require the user to move the mouse around. There are several types of click manipulation.
Click and drag manipulations can be tied into the plugin system – your plugin sees a manipulation as a change to a plugin-created dataref. This makes it possible to create almost any imaginable mouse effect. If you don’t want to write a plugin, you can still write up the manipulators to any of X-Plane’s datarefs (there are thousands) or commands (we’re getting up toward the 1000 mark on these too).
To create manipulators on your cockpit, you can use the latest plugin for AC3D. A manipulator is a property on a mesh within your object – each mesh can have its own manipulation with its own properties.
X-Plane does not have an IK solver. Rather, movement of “stuff” in your cockpit is indirect.
- Your manipulator changes a dataref as the user drags along an axis.
- The dataref change shows as an animation on your mesh.
Fortunately, ac3d has a “Guess” button for the axis manipulators. If you set a mesh to be manipulated by dragging along an axis, the guess button will examine your animations and suggest an axis that will create the most “natural” looking animation for the manipulation. For example, if you have a throttle handle that rotates, the guess button will provide a drag axis perpendicular to the throttle (to push the levers); if you have a throttle lever that pushes, the guess button will make a drag axis that runs along the lever.
There is no need to use the 3-d panel if you only want 3-d cockpit.
That might be the most counter-intuitive statement in the entire universe. Let’s break it down and see what’s going on. Originally we had the 2-D panel. The 2-D panel was where you put your instruments for interior views. When 3-d cockpit support was added, the 2-D panel was used to create the panel texture – that is, the instruments texture for the 3-D cockpit.
Thiat worked for a while, but as handles became more complex, screens became larger, and as 3-D cockpits became a more complex, authors started to run into the system’s limitations. If the author wanted to create a huge panel, then the panel texture for the 3-D cockpit was huge. Furthermore, texture space for the instruments in the 3-D cockpit was wasted because the 2-D panel had to have windows on it.
With X-Plane and 9 we added the 3-D panel to fix these problems. The 3-D panel is a second panel whose sole purpose is to provide instruments as a texture for the 3-D cockpit. When you have a 2-D panel and a 3-D panel, the 2-D panel is used to draw the panel in 2-D viewing modes and 3-D panel is used only to create the panel texture for the 3-D cockpit. With this setup the 2-D panel can be huge, and the 3-D panel can be small and compact with no windows.
The 3-D panel solves a second problem as well. Often the overhead panel is drawn in perspective on the 2-D panel this perspective view is useless for texturing a true 3-D cockpit. With a 2-D panel and a 3-D panel, the author can draw the overhead in perspective for the 2-D panel, and orthographically for the 3-D panel.
Now here’s where things get complicated: if an airplane has no 3-D panel the 2-D panel is used for both the 2-D view and the 3-D cockpit. But some airplanes have only a 3-D cockpit. In this case, there is no reason to use the 3-D panel at all. You can simply use the 2-D panel for texturing the 3-D cockpit and not worry about the user seeing it; in a 3-D only plane the user will only see the panel as a texture for the 3-D cockpit.
This setup is confusing in name: how can you have a 2-D panel used for a 3-D cockpits? But it is an allowed configuration. In fact, it was the only configuration allowed in X-Plane 8.
In summary: a 3-D cockpit can use the 2-D panel or 3-D panel as its panel texture. If an airplane has no 2-D panel, then the 2-D panel can be used for the 3-D cockpits without problems. In this situation and there is no need for a 3-D panel.
(It might be better to think of the 2-D panel and three panels simply add his two panels so that you can have two different versions of the panel. The names to the panel and 3-D panel are really just labels.)
X-Plane doesn’t natively and directly support popup panels, but that doesn’t mean you can’t pop them up. Generic instruments have a dataref-driven set of show-hide fields. (The “filters”.)
Now what you might not have realized is: groups have filters too! So you can hide an entire group with one filter, and you can put premade instruments in the group.
So…even though the FMS is a premade instrument with no filter fields, by grouping it you can show and hide it.
Important: the backgrounds of instruments are not shown or hidden. So if you want to do this, customize the FMS to have a transparent background, and use a generic rotary to put a real background behind it. The rotary goes in the group, and thus it can show and hide.
One more tip: clicking in 2-d goes through one instrument to another, for historical reasons. So if you pop up an instrument, you might want to hide the instruments it popped up over so clicks don’t affect them.
Javier posted a video of his CRJ on the dev list today. I have not tried the plane, but there is no question from the video that it looks really good. What makes the video look so nice is the careful management of light. Part of this comes from careful modeling in 3-d, and part of it comes from maxing out all of X-Plane’s options for light.
But…what are the options for light on an airplane? I don’t know what Javier has done in this case, but I can give you a laundry list of ways to get lighting effects into X-Plane.
Model In 3-D
To really have convincing light, the first thing you have to do is model in 3-d. There is no substitute – for lighting to look convincing, X-Plane needs to know the true shape of the exterior and interior of the plane, so that all light sources are directionally correct. X-Plane has a very large capacity for OBJ triangles, so when working in a tight space like the cockpit, use them wisely and the cockpit will look good under a range of conditions.
You can augment this with normal maps in 940. Normal maps may or may not be useful for bumpiness, but they also allow you to control the shininess on a per-pixel basis. By carefully controlling the shininess of various surfaces in synchronization with the base texture, you can get specular hilights where they are expected.
The 2-D Panel
First, if you want good lighting, you need to use panel regions. When you use a panel texture in a 3-d cockpit with ATTR_cockpit, X-Plane simply provides a texture that exactly matches the 2-d cockpit. Since the lighting on the 2-d cockpit is not directional, this is going to look wrong.
When you use ATTR_cockpit_region, X-Plane uses new next-gen lighting calculations, and builds a daytime panel texture and a separate emissive panel texture. These are combined taking into account all 3-d lighting (the sun and cockpit interior lights – see below). The result will be correct lighting in all cases.
Even if you don’t need more than one region and havea simple 1024×1024 or 2048×1024 3-d panel, use ATTR_cockpit_region – you’ll need it for high quality lighting.
The 2-d panel provides a shadow map and gray-scale illumination masks. Don’t use them for 3-d work! The 2-d “global lighting” masks are designed for the 2-d case only. They are optimized to run on minimal hardware. They don’t provide the fidelity for high quality 3-d lighting – they can have artifacts with overlays, there is latency in applying them, and they eat VRAM like you wouldn’t believe. I strongly recommend against using them as a source of lighting for a 3-d cockpit.
To put this another way, you really want to have all global illumination effects be applied “in 3-d”, so that the relative position of 3-d surfaces is taken into account. You can’t do this with the 2d masks.
The 2-d panel lets you specify a lighting model for every overlay of every instrument – either:
- “Mechanical” or “Swapped” – this basically means the instrument provides no light of its own – it just reflects light from external sources.
- “Back-Lit” or “Additive” – this means the instrument has two textures. The non-lit texture reflects external light, and the lit texture glows on its own.
- “Glass” – the instrument is strictly emissive.
You can use 2-d overlays not only for instruments but also to create the lighting effect within instruments, e.g. the back-lighting on a steam gauge’s markings, or the back-lighting on traced labels for an overhead panel.
2-d overlays take their lighting levels from one of sixteen “instrument brightness” rheostats. You can carefully allocate these 16 rheostats to provide independent lighting for various parts of the panel.
The 3-d Cockpit
The 3-d cockpit allows you to specify 3 omni or directional lights. These can be placed anywhere in the plane, affect all interior objects, and can be tinted and controlled by any dataref. Use them carefully – what they give you is a real sense of “depth”. In particular, the 3-d lights are applied after animation. If a part of the cockpit moves from outside the light to into the light, the moving mesh will correctly change illumination. This is something you cannot do with pre-baked lighting (e.g. a _LIT texture).
Finally, ATTR_light_level is the secret weapon of lighting. ATTR_light_level lets you manually control the brightness of _LIT texture for a given submesh within an OBJ. There are a lot of tricks you can do with this:
- If you know how to pre-render lighting, you can pre-render the glow from a light onto your object into your _LIT texture, and then tie the brightness of the _LIT texture to a dataref. The result will be the appearance of a glow on your 3-d mesh as the light brightens. Because the lighting effect is pre-calculated, you can render an effect that is very high quality.
- You can create back-lit instruments in 3-d and link the _LIT texture to an instrument brightness knob.
- You can create illumination effects on the aircraft fuselage and tie them to the brightness of a beacon or strobe.
There are two limitations of ATTR_light_level to be aware of:
- Any given triangle in your mesh can only be part of a single ATTR_light_level group. So you can’t have multiple lighting effects on the same part of a mesh. Plan your mesh carefully to avoid conflicts. (Example: you can’t have a glow on the tail that is white for strobes and red for beacons – you can only bake one glow into your _LIT texture.)
- ATTR_light_level is not available on the panel texture. For the panel texture, use instrument brightness to control the brightness of the various instruments.
I have a sample plane that demonstrate a few of these tricks; I will try to post it on the wiki over the next few days.
I’m not sure if these will make it into X-Plane 9.30 (we’re trying to close down features, but it doesn’t do much good to hold off features that help people make airplanes) but…while I was in Italy I created a few more manipulator types.
The set of manipulators let you change the value of a dataref directly with a mouse-click – the various flavors control how the dataref is changed.
These manipulators are the natural corollary to the command manipulator, which runs a command on a click.
Why have both? Commands are good, but they don’t cover 100% of sim functionality (just like datarefs don’t cover 100% of sim functionality). By having both, it will be possible to control switches and buttons that are best accessed by a dataref change.
For the basics on commands vs. datarefs, see here
The generic instruments already write to both commands (via the trigger instrument) and datarefs (via the rotary instrument) – these new manipulators provide the same functionality for 3-d cockpits.
X-Plane’s panel system does not have true “masking” based on a bitmap. You can clip an instrument to its rectangular region, but most masks are made by overlaying another layer or instrument on top of the moving parts. Examples include the circular mask for the moving map and the outside of the artificial horizon dial.
If you are using ATTR_cockpit then what you see in the OBJ is just like what you see in the 2-d panel, and the masking problem is simple: pick a mask that matches your background. In particular, if the back of the panel is black, your mask must be black; if the back of your panel has a gradient, the mask must contain a copy of a slice of the gradient.
But there are two cases where this rule does not work the way you might expect.
Masks for 2-d Spotlights
The 2-d spotlight textures (panel-2, panel-3, etc.) have a strange property: they light the background of the panel (the “burned in layer”) per-pixel but the overlays are lit per vertex. This is a cheat to keep the frame-rate high.
Normally this is not a problem – the moving parts are small and look different enough from the background that the lighting mismatch is not visible. But if you have a mask in the 2-d panel and spot lights, it will not match!
Unfortunately there is not much you can do about this. The only thing you can do is to keep the spotlight color uniform over the entire mask region.
Masks for Cockpit Regions
When you use ATTR_cockpit_region, the lighting model for your 3-d cockpit changes: instead of drawing the panel (as you saw it in 2-d), X-Plane calculates the albedo (day-time) and emissive (“_LIT”) components of the panel separately and then combines them with real 3-d lighting.
The good news is that the spot light problem is no longer a problem. Since the spot lights are 3-d and are applied to these final “panel textures”, a mask that matches the background will blend perfectly.
But in order to mask, you need to know which part of the panel texture you are masking (albedo or emissive!). If you are masking the albedo texture (e.g. a mechanical artificial horizon), create a mask that looks just like the panel background.
But for a glass instrument, the moving parts go into the emissive layer. Your mask must be pure black! Where did I get that from? The emissive layer adds light to the object. Black is an absence of adding light. So pure black ‘erases’ any light-only elements (which include all glass EFIS instruments, etc.).
One nice thing about this strategy: you can build a custom glass instrument (with a black mask) and put it over any background. This means you can reuse your art assets no matter how they are positioned on the panel.
I have said this before, but now it’s finally true: new file specifications are subject to change in the middle of beta!
In particular ATTR_light_level has changed slightly from beta 7 to beta 8. If you are using this feature in your objects, you will need to update your objects.
A new ac3d beta will be posted later today that supports the updated syntax.
You can read about the syntax here.