This is a fairly good article on how manipulators work. I've been doing some manipulators recently and it took a while to understand it.
https://around-the-corner.typepad.com/adn/2012/10/maya-custom-manipulators-.html
One of the key points is that when you connect the plug to the manipulator, it is a 1:1 relationship that exactly keeps the units the same.
e.g.
fnCurvePoint.connectToCurvePlug(curvePlug); //This sets up a 1:1 relationship
If you want to do something different than a 1:1 relationship, you have to not use the connectToPlug method, but actually use callbacks instead. Even if you want to do a conversion (radians to degrees) you have to use the callback method (which is super frustrating).
To do that you need to get the index of the specific manipulator pieces (e.g disc has 3 elements - its position, axis orientation and the angle itself). You need this index later to use in the callback.
unsigned discAngleIndex = fnDisc.angleIndex();
unsigned discCenterIndex = fnDisc.centerIndex();
unsigned discAxisIndex = fnDisc.axisIndex();
To add the callback, its like this...
addPlugToManipConversionCallback(discCenterIndex, (plugToManipConversionCallback)&MyNodeManip::discCenterCallback);
For the callback code you need to check that the index matches up with the proper element, and then
MManipData MyNodeManip::discCenterCallback(unsigned manipIndex) {
if (manipIndex == discCenterIndex ) {
MManipData manipData;
MFnNumericData numData;
MObject numDataObj = numData.create(MFnNumericData::k3Double);
numData.setData(center.x, center.y, center.z);
manipData = numDataObj;
return manipData;
}
}
I hope it helps and wish I would have known the above info before writing manipulators.
