From: Paul Brannan <pbrannan@...>
Date: 2001-11-08T05:30:18+09:00
Subject: [ruby-talk:24590] Re: OpenGL (rbogl) bindings to Tk?

On Thu, 8 Nov 2001, Phlip wrote:

> Rubies:
>
> I have wrapped my Mandrake 7.2 around Yoshi's Ruby OpenGl binding
> (rbogl-0.32a.tgz), and have a couple very pedestrian comfort zone
> issues with it...
>
>  - how to put it in a Tk widget instead of a free floating window?

For this I think you need to get a Tk OpenGL widget and wrap it.  I
generally use Gtk, which has a gtkglarea.  I'm not sure which Tk widget
provides something like this, but a search on google for seems to bring up
some entries.

>  - how to click on it and get the viewed object to rotate

You need to grab mouse down and mouse motion events, and coordinates of
the mouse in 2D space when these events occur.  You can then use
quaternions or spaceballs or whatever other mechanisms you wish to
calculate the rotation matrix for the object, then pass that to GL.Rotate.
You can find some (C/C++) tutorials on this at nehe.gamedev.net and
www.gamasutra.com.

> You can see I'm spoiled by bigger ready-made front-end solutions such
> as Blender, Visualization Toolkit, Coin3d, the VRML viewers, CernRoot,
> CrystalSpace, SciLab, PyOpenGl, OpenDX, GnuPlot, QuesaLibrary, etc.
>
> Will roll my own if someone reveals I have to...

You may have to do that, though I'm sure someone has already written a
library to do basic rotations and translations.  Perhaps a wrapper for
CrystalSpace would be in order...

Here's a simple example of how to do basic rotations with the mouse using
GLUT (based on cube.rb that comes with the opengl extension):

require 'opengl'
require 'glut'

class Cube
  FACES = [[0,1,2,3],[3,2,6,7],[7,6,5,4],[4,5,1,0],[5,6,2,1],[7,4,0,3]]
  VERTS =
[[-1,-1,1],[-1,-1,-1],[-1,1,-1],[-1,1,1],[1,-1,1],[1,-1,-1],[1,1,-1],[1,1,1]]

  def display
    GL.Clear(GL::COLOR_BUFFER_BIT)
    GL.Begin(GL::QUADS)
    FACES.each do |face|
      face.each do |vert|
        GL.Vertex(VERTS[vert])
      end
    end
    GL.End()
    GLUT.SwapBuffers
  end

  def mouse(button, state, x, y)
    @x0 = x; @y0 = y
    @state = state
  end

  def motion(x, y)
    if @state == GLUT::DOWN then
      GL.Rotate(@x0 - x, 0.0, 1.0, 0.0)
      GL.Rotate(@y0 - y, 1.0, 0.0, 0.0)
      @x0 = x; @y0 = y
      GLUT.PostRedisplay
    end
  end

  def initialize
    GLUT.Init
    GLUT.InitDisplayMode(GLUT::DOUBLE | GLUT::RGB)
    GLUT.CreateWindow("cube")
    GLUT.DisplayFunc(method(:display).to_proc)
    GLUT.MouseFunc(method(:mouse).to_proc)
    GLUT.MotionFunc(method(:motion).to_proc)

    GL.MatrixMode(GL::PROJECTION)
    GLU.Perspective(40.0, 1.0, 1.0,  10.0)
    GL.MatrixMode(GL::MODELVIEW)
    GL.PolygonMode(GL::FRONT_AND_BACK, GL::LINE)
    GLU.LookAt(0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0)

    @state = nil
  end

  def go
    GLUT.MainLoop()
  end
end

Cube.new.go

--
Paul