RE: [Plib-users] OpenGL primitives

[Norman V. <nh...@ca...>]

Stafford Goodsell writes
>Sent: Thursday, June 08, 2000 9:28 PM
>To: pli...@li...
>Subject: [Plib-users] OpenGL primitives
>
>
>
>Hi,
>
>Also, the reason i need to debug this code so intensely is 
>because it seems that the axes are different depending on 
>if you are rotating or translating... 
>for translating x appears to be -, y is |, and z is . (into 
>the screen), but for rotations, x is around |, y is around -, 
and z is the same. 

My guess is that you are confused by the difference between the
coordinate systems used by SSG and OpenGL.

In OpenGL Z is going in and out of the screen
whereas in SSG Z is up down or Y in OpenGL

To convert from  SSG to OpenGL you can use the following
// hack
sgMat4 copy_of_ssgOpenGLAxisSwapMatrix =
{
  {  1.0f,  0.0f,  0.0f,  0.0f },
  {  0.0f,  0.0f, -1.0f,  0.0f },
  {  0.0f,  1.0f,  0.0f,  0.0f },
  {  0.0f,  0.0f,  0.0f,  1.0f }
} ;

sgMat4 vm_tmp, view_mat;
sgTransposeNegateMat4 ( vm_tmp, current_view.VIEW ) ;
sgCopyMat4( view_mat, copy_of_ssgOpenGLAxisSwapMatrix ) ;
sgPreMultMat4( view_mat, vm_tmp ) ;
glLoadMatrixf( (float *)view_mat );

Nice Looking Helicopter :-))

Have you checked out FlightGear.
http://www.flightgear.otg

It is using SSG for the majority of its rendering
and comes with source. 

Norman Vine