quat.multiply not giving correct values

Hi Pete,

It might be a bit tricky to directly modify the quaternion in order to map rotation (as it doesn't store euler angles directly). Have you considered using slerp in order to do rotation mapping instead?

Something like:

// @input SceneObject source

var sourceT = script.source.getTransform();

function update(){

// a vector facing the right side, so that
// when source object is facing right, dot will be -1
// when source is facing left, dot will be 1
var v1 = new vec3.right();
v1.y = 0; // Zero out the vertical offset to constrain rotation to Y axis

// rotation of source object which will determine how far I should rotate my object
var v2 = sourceT.forward;
v2.y = 0; // Zero out the vertical offset to constrain rotation to Y axis

// figure out how far current rotation is from the reference rotation
var dot = v1.dot( v2 );

// Since dot will go from -1 to 1, we need to map it so that it's from 0 to 1
var percentage = (dot + 1)/2

// Map the Rotation
// in this case when my source object is looking right, I want my object to look straight (beginRot)
// when my source object is looking left, I want my object to look left (finalRot)
var beginRot = quat.angleAxis(0, vec3.up());
var finalRot = quat.angleAxis(Math.PI/2, vec3.up());
var newRot = quat.slerp(beginRot, finalRot, percentage);

script.target.getTransform().setWorldRotation(newRot)
}
script.createEvent("UpdateEvent").bind(update);

The other reason why you want to use quaternion function directly is that we might get gimbal lock issues when trying to convert to euler rotation first. 

Let me know if this makes sense or if I misunderstood your question.

Cheers!

Jonathan