From: George Ogata <g_ogata@...>
Date: 2006-03-10T05:03:43+09:00
Subject: Re: Is the key delaying interpretation of a variable?

"anne001" <anne@wjh.harvard.edu> writes:

> To clarify the question
>
> upperarm = Node.new(scale, translation, jointP, rotation,&draw)
>
> is going to initialize
> @rotation= [0,0,0,1]
>
> How can I initialize it with
> @rotation=[$shoulder, 0,0,1]
>
> so when the gl and glut command comes along what it sees is
> rotate([$shoulder, 0,0, 1])...
> and not
> rotate([0,0,0,1])
>
> How do I prevent ruby from interpreting $shoulder so glut can have a go
> at it? 
>
> How do I delay the interpretation of this parameter?

I'd question how your code is structured.  You're correct in that once you do:

  @rotation = [$shoulder, 0, 0, 1]

....changing $shoulder:

  $shoulder = 90

....won't change @rotation[0].

A few options come to mind:

  1.  Provide funky angle accessors that modify the @rotation array instead:

  class Node
    def angle
      @rotation[0]
    end
    def angle= val
      @rotation[0] = val
    end
  end
  
  upperarm = Node.new(...)
  upperarm.angle = 90

  2.  Store the rotation angle and axis separately:

  class Node
    def initialize(angle, axis, ...)
      @angle = angle
      @axis  = axis
      ...
    end
    attr_accessor :angle, :axis

    def draw
      ...
      rotate(@angle, *@axis)
      ...
    end
  end

  3.  If you insist on using a global, use it in place of "@angle" in 2.

  class Node
    def initialize(axis, ...)
      @axis  = axis
      ...
    end
    attr_accessor :axis

    def draw
      ...
      rotate($shoulder, *@axis)
      ...
    end
  end

HTH.