I have an object (obj1) that creates a button.
self.createButton({ position={ 15.7, 0.1, -1.8 }, ...})
That position, of course, is relative to obj1.
obj1 is a bag, and the button it creates is on the game board, far away from the bag (as you can tell by the magnitude of the X component). This isn't appropriate, and it means the bag can't be moved. I want to have the game board create the button instead.
How do I determine the coordinates to provide when calling createButton from within the game board (obj2)?
I worked out that one can translate the relative position to an absolute position using the following:
local rel_pos = Vector(15.7, 0.1, -1.8)
local abs_pos = Vector(-v[1], v[2], v[3])
abs_pos:scale( obj1.getScale() )
abs_pos:rotateOver('z', obj1.getRotation()['z'] ) -- The order is important
abs_pos:rotateOver('x', obj1.getRotation()['x'] )
abs_pos:rotateOver('y', obj1.getRotation()['y'] )
abs_pos:add( obj1.getPosition() )
Reversing the process using obj2 will get the vector to use in obj2.
But why is the X component negated? I thought I was missing something until I discovered positionToWorld, a function meant to do exactly what the above attempts. It turns out I still needed to negate the X component.
local rel_pos = Vector(15.7, 0.1, -1.8)
local abs_pos = obj1.positionToWorld(Vector(-v[1], v[2], v[3]))
I can only conclude that that createButton has a bug that requires one to negate the X component of the position it is provided.
The following is the complete solution:
local v = Vector(15.7, 0.1, -1.8)
v:setAt(1, -v[1]) -- Bug-compensated loc rel to obj1 -> Loc rel to obj1
v = obj1.positionToWorld(v) -- Loc rel to obj1 -> Absolute loc
v = obj2.positionToLocal(v) -- Absolute loc -> Loc rel to obj2
v:setAt(1, -v[1]) -- Loc rel to obj2 -> Bug-compensated loc rel to obj2
print(logString(v))
The final result was replacing
-- In obj1 (the bag)
self.createButton({ position={ 15.7, 0.1, -1.8 }, ... })
with
-- In obj2 (the game board)
self.createButton({ position={ -7.745875, 13.7634, -1.006971 }, ... })