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Customized Geometry Nodes

In order to implement geometry nodes with special objects not covered by the basic geometry types (boxes, tetrahedra, prisms, spheres etc.) we derive from mininode_geom and override the following three virtual methods:

  • rendergeo: render geometric primitives
    • front facing triangles are specified counter-clock-wise
    • back facing triangles are culled
    • normals are specified to face outward
    • a head light shader is applied by default
    • inward facing normals are flipped when shaded
  • getbbox: provide information about the bounding box of the primitives
  • shoot: compute the intersection of a ray with the geometric primitives
    • by default the hit point is approximated by the intersection with the bounding sphere
    • if exact hit points are required, override the shoot method and provide exact calculations

See the mininode_teapot.cpp module as an example:

mininode_geometry_teapot::mininode_geometry_teapot()
   : mininode_geom()
   {}

void mininode_geometry_teapot::rendergeo()
   {
   glDisable(GL_CULL_FACE);

   glVertexPointer(3,GL_FLOAT,0,teapotVertices);
   glEnableClientState(GL_VERTEX_ARRAY);
   glNormalPointer(GL_FLOAT,0,teapotNormals);
   glEnableClientState(GL_NORMAL_ARRAY);

   drawTeapotElements();

   glDisableClientState(GL_VERTEX_ARRAY);
   glDisableClientState(GL_NORMAL_ARRAY);

   glEnable(GL_CULL_FACE);
   }

void mininode_geometry_teapot::getbbox(miniv3d &bboxmin,miniv3d &bboxmax) const
   {
   bboxmin=miniv3d(-3,0,-2);
   bboxmax=miniv3d(3.434,3.15,2);
   }

double mininode_geom::shoot(const miniv3d &o,const miniv3d &d,double mindist) const
   {return(shootbsphere(o,d,mindist));}
[Get Code]

We put the teapot at the place where it belongs to - the Utah Science and Imaging Institute (SCI):

mininode_ref teapot = new mininode_geometry_teapot;

minicoord utah;
utah.set_llh(40.767690,-111.845037); // utah science and imaging institute (sci)

group->append_child(new mininode_coord(utah))->
   append_child(new mininode_color(miniv3d(0.9, 0.9, 0.9)))->
   append_child(new mininode_scale(10000.0))->
   append_child(new mininode_translate(miniv3d(0.0, 0.0, 0.1)))->
   append_child(new mininode_rotate(90, miniv3d(1.0, 0.0, 0.0)))->
   append_child(teapot);
[Get Code]


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