Can MotionPath be made circular, or elliptical?

Troubleshooting General Help
1

The topic is in the title. It’d be very useful for such things as making planets travel on an orbit without the fuss of physics. Setting CurveTension to 1 makes an almost-circular path, but it’s not what I’m after.



Any tips before I go code an orbital PathInterpolation?

2

Hang on, maybe I should just approximate what I’m after with more waypoints. Sorry, guys.

3

in TestCameraMotionPath i achieved a circular path with 4 waypoints and a tension of about 0.8.

You should check the testcase

4

Thanks for that! Some easy math and using 20 waypoints per orbit I’m getting near perfect ellipses :smiley:

5

cool!

May I ask you if you could post the code? it could be a useful snippet.



thanks

6

Not sure how snippets work, but here goes:



pre type="java"[java]// This snippet of code takes an x value (X) and an eccentricity value (E), and produces an elliptical path around the origin. It should be straight-forward to adapt to other uses.



float x = (float) X;

// Do calculation from http://www.1728.com/ellipse.htm

float y = (float) (X * Math.sqrt(1 - Math.pow(E, 2)));

// Find one of the ellipses foci, to orbit around.

float foci = (float) Math.sqrt(Math.pow((x/2), 2) - Math.pow((y/2), 2));



final float numberOfWaypoints = 20;



MotionPath path = new MotionPath();

for (int i = 0; i < numberOfWaypoints; i++) {

path.addWayPoint(new Vector3f((float) (Math.cos((i * 2 * Math.PI)/numberOfWaypoints) * x) + foci, 0, (float) Math.sin(i * (2 * Math.PI)/numberOfWaypoints) * y));

}

path.enableDebugShape(assetManager, rootNode);

// Tension might need a little adjusting depending on how many waypoints you want. I think

// 0.5 is acceptable for 20 waypoints.

path.setCurveTension(0.5f);

path.setCycle(true);[/java]/pre