From: Phlip <phlip_cpp@...>
Date: 2001-12-03T02:00:17+09:00
Subject: [ruby-talk:27283] Is there a geometer in the house? (OpenGL Translate vs POVray Translate)

Jean-Marc van Leerdam wrote:

> Keep in mind that the OpenGL origin 'moves with the translations'
> whereas the POV origin is fixed.

Therein lies the rub. Compare:

// POVray

cylinder {<0,0,0>,<0,59.0625,0>, 3.32227
           pigment{col_2}
            finish  {ambient 0.3 diffuse 0.7 phong 1}
           rotate < 0, 0, -32.8296> rotate < 0, -99.4838, 0>
           translate < 0, 175, 0>}

//OpenGL

 GL::Rotate(@whyRotation, 0, 0, 1)
 GL::Rotate(@zeeRotation, 0, 1, 0)

  GL::Translate (
                @exxTranslation,
                @whyTranslation, 
                0 # @zeeTranslation,
                )
 
    GLU::Cylinder(quad, @radius, @radius, @height, SLICES_NUMBER, 
STACKS_NUMBER)

The POVray script builds the object at the origin, then rolls it around Z, 
then rolls it around Y, then moves it out to its final location.

The OpenGL code creates a matrix that rolls around Y (formerly Z), rolls 
around Z (formerly Y), then translates.

(Swapping Y and Z is a pain, but it works on Cylinders with several other 
rotations and translations besides this one.

So regardless of how OpenGL rotates after a translation, we are using 
POVray in an OpenGL-compatible way, by rotating first and then translating.

Below my sig is source closer to the actual problem. I took the Translate 
call out and let glshapes.rb handle it internally. The V is now on top of 
the I, with only a small break between them.

-- 
Phlip

#!/usr/bin/env ruby

require 'fox'
require 'opengl'
require 'fox/glshapes'
include Fox


class GLViewWindow < FXMainWindow

  ID_GLVIEWER = enum(FXMainWindow::ID_LAST, 1)[0]

  def initialize(app)
    super(app, "Bad Thing Test", nil, nil, DECOR_ALL, 0, 0, 800, 600)
    @mdiclient = FXMDIClient.new(self, LAYOUT_FILL_X|LAYOUT_FILL_Y)
    mdichild = FXMDIChild.new(@mdiclient, "FOX GL Viewer", @mdiicon,
      nil, MDI_MAXIMIZED, 30, 30, 300, 200)
    @glvisual = FXGLVisual.new(getApp(), VISUAL_DOUBLEBUFFER)
    @mdiclient.setActiveChild(mdichild)
    viewer = FXGLViewer.new(mdichild, @glvisual, self, ID_GLVIEWER,
      LAYOUT_FILL_X|LAYOUT_FILL_Y|LAYOUT_TOP|LAYOUT_LEFT)

    @scene = FXGLGroup.new
    gp2 = FXGLGroup.new
    @scene.append(gp2)
    

        addCylinder gp2, 59.0625, 3.322265625, 2, -32.82964323, 
-99.48376736, [0.0, 0.0, 175.0], [-5.319876145, 30.17051687, 222.1752194]

        addCylinder gp2, 44.296875, 1.868774414, 2, -65.65928646, 
-99.48376736, [-5.319876145, 30.17051687, 222.1752194], [-12.01231147, 
68.12520364, 239.3344216]
        
        addCylinder gp2, 44.296875, 1.868774414, 2, -32.82964323, 
-99.48376736, [-5.319876145, 30.17051687, 222.1752194], [-9.309783254, 
52.79840451, 257.556634]
    
    viewer.setScene(@scene)
  end


        def addCylinder gp, length,thickness,pigment,zeeRotation,whyRotation,
                 xyzTranslation, xyzEnd
                 
                exxTranslation, whyTranslation, zeeTranslation = xyzTranslation

        cyl = Cylinder.new ( exxTranslation, whyTranslation,
                                                zeeTranslation, length,  thickness )
          
                cyl.zeeRotation = zeeRotation
                cyl.whyRotation = whyRotation
                gp.append(cyl)
   
    end


  def create
    super
    show(PLACEMENT_SCREEN)
  end

end

def run
  application = FXApp.new("GLViewer", "FoxTest")
  application.disableThreads
  application.init(ARGV)
  GLViewWindow.new(application)
  application.create
  application.run
end


class Cylinder < FXGLCylinder
  def initialize(*args)
        super(*args)
        @zeeRotation = 0
        @whyRotation = 0
        
  end
  
  attr_writer :zeeRotation, :whyRotation
  
  def drawshape(viewer)
    quad = GLU::NewQuadric()
    GLU::QuadricDrawStyle(quad, GLU::FILL)
    GL::PushMatrix()

    GL::Rotate(@whyRotation, 0, 0, 1)
    GL::Rotate(@zeeRotation, 0, 1, 0)

    GLU::Cylinder(quad, @radius, @radius, @height, SLICES_NUMBER, 
STACKS_NUMBER)
    
    GLU::QuadricOrientation(quad, GLU::INSIDE)
    GLU::Disk(quad, 0, @radius, SLICES_NUMBER, LOOPS)
   
    GLU::QuadricOrientation(quad, GLU::OUTSIDE)
    GLU::Disk(quad, 0, @radius, SLICES_NUMBER, LOOPS)
    
    GL::PopMatrix()
    GLU::DeleteQuadric(quad)
  end
end


run