# Is the key delaying interpretation of a variable? **URL:** \ **Category:** Ruby\ **Created:** [March 7, 2006, 1:44pm UTC](https://www.ruby-forum.com/t/is-the-key-delaying-interpretation-of-a-variable/77802 "2006-03-07T13:44:47Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![anne001](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/34f0e0/32.png) [@anne001](https://www.ruby-forum.com/u/anne001)\ **Post date:** [March 7, 2006, 1:44pm UTC](https://www.ruby-forum.com/t/is-the-key-delaying-interpretation-of-a-variable/77802/1 "2006-03-07T13:44:47Z")
I am modifying robot.rb in opengl’s sample directory, the original robot turns, mine does not! snif… The original example goes something like this A display proc display = Proc.new { … GL.Rotate($shoulder, 0.0, 0.0, 1.0); … } a keyboard proc keyboard = Proc.new {|key, x, y| case (key) when ‘s’[0] $shoulder = ($shoulder + 5) % 360; GLUT.PostRedisplay(); Then you tell glut the name of those procs GLUT.DisplayFunc(display); Glut.KeyboardFunc(keyboard); * * * The new program goes like this def displaytree … traversetree … end def traversetree applytransform … end def applytransform … GL.Rotate(\*@rotation); end … and in the initialization definition @rotation = [$shoulder, 0.0, 0.0, 1.0] ## GLUT.DisplayFunc(lambda{trunk.displaytree}); GLUT.KeyboardFunc(keyboard); The first program rotates, the second one does not. I am wondering if it has something to do with the 2nd method estimating $shoulder in a different way from the first method? @rotation is probably evaluated before creating the new object, and after that this line is never accessed? So my display does not have a $shoulder parameter to update? scale=[2.0, 0.4, 1.0] jointP=[-1, 0, 0] translation=[$shoulderposx, $shoulderposy, 0.0] rotation = [$shoulder, 0.0, 0.0, 1.0] draw = Proc.new { GLUT.WireCube(1.0)} upperarm = Node.new(scale, translation, jointP, rotation,&draw) How can I keep the $shoulder parameter physically with all the other parameters defining the shoulder definitions, and still have $shoulder update with keyboard presses? ---
**Author:** ![anne001](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/34f0e0/32.png) [@anne001](https://www.ruby-forum.com/u/anne001)\ **Post date:** [March 7, 2006, 4:39pm UTC](https://www.ruby-forum.com/t/is-the-key-delaying-interpretation-of-a-variable/77802/2 "2006-03-07T16:39:29Z")
To clarify the question upperarm = Node.new(scale, translation, jointP, rotation,&draw) is going to initialize @rotation= [0,0,0,1] How can I initialize it with @rotation=[$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 $shoulder so glut can have a go at it? How do I delay the interpretation of this parameter? ---
**Author:** ![anne001](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/34f0e0/32.png) [@anne001](https://www.ruby-forum.com/u/anne001)\ **Post date:** [March 7, 2006, 7:54pm UTC](https://www.ruby-forum.com/t/is-the-key-delaying-interpretation-of-a-variable/77802/3 "2006-03-07T19:54:30Z")
anne001 wrote: > so when the gl and glut command comes along what it sees is > rotate([$shoulder, 0,0, 1])… > and not > rotate([0,0,0,1]) > > How do I prevent ruby from interpreting $shoulder so glut can have a go > at it? > > How do I delay the interpretation of this parameter? Maybe something like this… but dont know whether it is going to be helpful: a=nil l=lambda{ [a,0,0,0] } a=5 p l[] lopex ---
**Author:** ![anne001](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/34f0e0/32.png) [@anne001](https://www.ruby-forum.com/u/anne001)\ **Post date:** [March 9, 2006, 9:05pm UTC](https://www.ruby-forum.com/t/is-the-key-delaying-interpretation-of-a-variable/77802/4 "2006-03-09T21:05:44Z")
“anne001” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes: > so when the gl and glut command comes along what it sees is > rotate([$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: $shoulder = 90 …won’t change @rotation[0]. A few options come to mind: 1. Provide funky angle accessors that modify the @rotation array instead: class Node def angle @rotation[0] end def angle= val @rotation[0] = val end end upperarm = Node.new(…) upperarm.angle = 90 1. Store the rotation angle and axis separately: class Node def initialize(angle, axis, …) @angle = angle @axis = axis … end attr\_accessor :angle, :axis ``` def draw ... rotate(@angle, *@axis) ... end ``` end 1. If you insist on using a global, use it in place of “@angle” in 2. class Node def initialize(axis, …) @axis = axis … end attr\_accessor :axis ``` def draw ... rotate($shoulder, *@axis) ... end ``` end HTH. ---
**Author:** ![anne001](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/34f0e0/32.png) [@anne001](https://www.ruby-forum.com/u/anne001)\ **Post date:** [March 18, 2006, 9:27pm UTC](https://www.ruby-forum.com/t/is-the-key-delaying-interpretation-of-a-variable/77802/5 "2006-03-18T21:27:11Z")
Thank you so much for your response. I had tried Marcin’s suggestion, but got error messages. I have been wondering what to do, and then I saw your suggestion from last week, and suddenly what you were saying clicked! > If you insist on using a global > That’s it! In the original program, $shoulder is a global so various > parts of the > program can access it. It holds the memory of the system. Having rewritten the program an OOP way, this is no longer necessary. The object holds the memory of the system! So I changed the keyboard proc to say keyboard = Proc.new {|key, x, y| case (key) when ‘s’[0] upperarm.rotation[0] = (upperarm.rotation[0] + 5) % 360; GLUT.PostRedisplay(); and now it all works fine. I hadn’t really understood what the keyboard proc was doing! Thank you!!! I can move on again! wonderful.