How Objects are Drawn in the Viewport

The following steps describe how a simple object is drawn in the viewport.

1. The object's drawing code is in its override BaseObject::Display() method. An INode and a ViewExp are passed into this method.
2. The implementation of BaseObject::Display() calls INode::GetObjectTM(). This method returns the matrix that is used to transform the points of the object from object space to world space.
3. The BaseObject::Display() method then takes the matrix returned from INode::GetObjectTM() and sets it into the graphics window (using GraphicsWindow::setTransform()). In this way, when the object starts drawing points in object space, they will be transformed with this matrix. This puts them into world space as they are drawn.

Below is the code from the SimpleObject implementation of BaseObject::Display().

int  SimpleObject::Display(TimeValue t,
         INode* inode,
         ViewExp *vpt,
         int flags)
{
   if (!OKtoDisplay(t)) return 0;
   GraphicsWindow *gw = vpt->getGW();
   Matrix3 mat = inode->GetObjectTM(t);
   UpdateMesh(t); // UpdateMesh just calls BuildMesh() if req'd at time t.

   gw->setTransform(mat);
   mesh.render( gw, inode->Mtls(),
         (flags&USE_DAMAGE_RECT) ? &vpt->GetDammageRect() : NULL, COMP_ALL,
         inode->NumMtls());
   return(0);
}