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[BrazilianBoy]

How can I discover the Y rotation of a vector lying on the Y plane, having another vector lying on the Y plane as an origin?

Lucas.

[Marvin Fröhlich]

If you simply want the angle between these two vectors, you can simply use the vec1.angle( vec2 ) method. But you have to handle the fact, that this angle is constrained to [0, PI]. So you have to use some other information to convert this angle from [0, PI] to [0, 2PI]. this could work like this:

Let's say the original vector is always Vector3f.POSITIVE_X_AXIS. Then you can do it like this:

Code:

Vector3f v = [your vector with y = 0];
float angle = v.angle( Vector3f.POSITIVE_X_AXIS );
if ( v.z > 0f )
    angle = FastMath.TWO_PI - angle;

Marvin