Key Frames in Version 9 (and datarefs)

X-Plane 9 will feature key-framed animation for the rotation and translation animations (but not the show-hide animations). Basically:

• You can have more than two key frames.
• Interpolation between them is linear.
• Extrapolation off the ends is linear (use two equal-value key frames to clamp).

Key frames will be available for all OBJs: scenery, cockpit and aircraft parts. I will try to post a spec soon - the implementation is very similar to the RFC I posted a while ago.

(If you read the .tcl code in the AC3D plugin, you may have guessed that this was coming.)

Trigger

Now I know somebody is going to ask me: "will this allow me to make an animation X start when event Y happens in the sim?" The answer is: no! Key frames allow you to map the relationship between an input dataref and your geometry in any way you want. But if the input dataref is not changing, the output position cannot change either.

Example: you can use key frames to make complex things happen as the gear deploys. Gear deployment is a ratio that starts at 0 and slowly changes to 1 as the gear deploys (over the cycle time as set in PlaneMaker). So you can use this to make the wheels move forward first, then down.

But you cannot use key frames in the cockpit to make the gear handle move slowly. The gear handle dataref is really a switch - it instantly changes from 0 to 1. If you set up a nice key framed animation, we will instantly jump from the animation position at 0 to the animation position at 1.

In other words, whether or not you have key frames, the timing of an animation comes from datarefs, and datarefs alone. I am not planning any extensions to the OBJ system any time soon that will let you trigger animations from events. In other words, you can't synthesize timed sequences from an OBJ. (The purpose of OBJs is to visualize things, not model things.)

If you want to create timing data, write a plugin. If you don't know how to code, I have seen at least one plugin that lets authors "invent" simple datarefs using a text file.

No Spare Datarefs

And while I'm going off on a tangent about authoring and datarefs, we will not be adding any "spare" datarefs. Again, datarefs should be made with plugins, and non-programmers should use a plugin that creates datarefs from text files. We will not be creating any "unused" datarefs in the sim.

Why not? Think of the integration problems. Even if we make 100, what happens if Joe uses "spare dataref 93" in the cockpit of his great 747 and Fred uses "spare dataref 93" for the windmills turning in his scenery pack? Splat.

The naming convention of datarefs start with the company or author who created it - or "sim" for X-Plane itself. This is intentional - it assures that two independent authors won't use the same dataref name and create conflicts between add-ons!