fun rotation math that i just cant get right

It's a 2D rotation, but working the similar way I think.
Hope this helps.

Type face
	Global faces:TList = New TList
	
	Field x:Float
	Field y:Float
	Field rot:Float = 0
	Field radius:Float = 50
	Field anglimit:Float = 45
	
	Method render()
		SetColor(80, 80, 80)
		DrawOval(x - radius / 2, y - radius / 2, radius, radius)
		
		SetColor(255, 0, 0)
		DrawLine(x, y, Cos(rot) * radius * 1.5 + x, Sin(rot) * radius * 1.5 + y)
		
		SetColor(0, 0, 255)
		DrawLine(x, y, Cos(rot + anglimit) * radius * 1.2 + x, Sin(rot + anglimit) * radius * 1.2 + y)
		DrawLine(x, y, Cos(rot - anglimit) * radius * 1.2 + x, Sin(rot - anglimit) * radius * 1.2 + y)
	End Method
	
	Method New()
		faces.AddFirst(Self)
	End Method
	
	
End Type

Function faceeach(f1:face, f2:face)
	Local ca:Float = f1.rot
	Local ta:Float = ATan2(f2.y - f1.y, f2.x - f1.x)
	
	Local la:Float = f1.anglimit
	Local da:Float = ta - ca
	Local dif:Float = Abs(da) - la
	
	If dif > 0 Then
		Local da1:Float = Cos(da + la)
		Local da2:Float = Cos(da - la)
		If da1 >= da2 Then
			f1.rot = ta + la
		Else
			f1.rot = ta - la
		End If
	EndIf
End Function

Graphics(640, 480)

Local f1:face = New face
Local f2:face = New face

While Not KeyHit(KEY_ESCAPE)
	
	If MouseDown(1)
		f1.x = MouseX()
		f1.y = MouseY()
	End If
	
	If MouseDown(2)
		f2.x = MouseX()
		f2.y = MouseY()
	End If
	
	faceeach(f1, f2)
	faceeach(f2, f1)
	Flip
	Cls

	For Local f:face = EachIn face.faces
		f.render()
	Next
	
Wend

*EDIT* Sorry, this code is not correct...
I'll modify it.
But at least you can use it for testing.. lol


*EDIT2* It's working properly now I think.
The COS(da+la) is used instead of angle comparison.
It choose the smaller angle when diff > limit, in order to avoid the jumpping.