From: Bill Kelly <billk@...>
Date: 2001-11-13T12:36:38+09:00
Subject: [ruby-talk:24975] Re: FXGLViewer - rotate a primitive?

Hi Phlip,

From: "Phlip" <phlip_cpp@yahoo.com>
>
> Rubies:
> 
> Regarding this example code...
> 
> FXRuby-0.99.174/examples/glviewer.rb
> 
> ....open it up and eyeball this line:
> 
> gp2.append(FXGLCylinder.new(-1.0, 0.5, 0.0, 1.0, 0.5))
> 
> Now suppose I feel that vertical cylinders are boring. I want to
> rotate this cylinder (not the whole scene - just the cylinder) 30
> degrees over.
> 
> Does OpenGL miss this simple ability? The concept I'm trying to match
> is POVray script, which rotates all the time as part of Composite
> Solid Geometry.

My OpenGL's going on about 3+ years rusty, but, I can imagine
circumstances under which vertical cylinders might indeed be boring,
such as the hypothetical inability to make some less vertical than
others :-)

Check out robot.rb which should hopefully be found in your
rubygl-x.xx/samples directory. . .  a hierarchical "robot arm"
model built from a few 'box' primitives scaled and rotated relative
to one another.

Also, Ch. 4 of:
http://ask.ii.uib.no/ebt-bin/nph-dweb/dynaweb/SGI_Developer/OpenGL_PG/

(Plus there are a plethora of OpenGL examples at:
http://www.opengl.org/developers/code/samplecode.html )


HTH,

Bill

P.S. Your mention of CSG in POVRay reminded me of an article about
doing fast (dynamic) CSG in OpenGL using the stencil buffer:
http://www.sgi.com/software/opengl/advanced97/notes/node11.html