OpenGL Programming Guide

Chapter 4Display Lists

Creating and Executing a Display List

Hierarchical Display Lists

You can create a hierarchical display list, which is a display list that executes another display list, by calling glCallList() between a glNewList() and glEndList() pair. A hierarchical display list is useful for an object that's made of components, especially if some of those components are used more than once. For example, this is a display list that renders a bicycle by calling other display lists to render parts of the bicycle:

glNewList(listIndex,GL_COMPILE);
   glCallList(handlebars);
   glCallList(frame);
   glTranslatef(1.0,0.0,0.0);
   glCallList(wheel);
   glTranslatef(3.0,0.0,0.0);
   glCallList(wheel);
glEndList();

To avoid infinite recursion, there's a limit on the nesting level of display lists; the limit is at least 64, but it might be higher, depending on the implementation. To determine the nesting limit for your implementation of OpenGL, call

glGetIntegerv(GL_MAX_LIST_NESTING, GLint *data);

OpenGL allows you to create a display list that calls another list that hasn't been created yet. Nothing happens when the first list calls the second, undefined one.

You can use a hierarchical display list to approximate an editable display list by wrapping a list around several lower-level lists. For example, to put a polygon in a display list while allowing yourself to be able to easily edit its vertices, you could use the code in Example 4-6 .

Example 4-6 : Using a Hierarchical Display List

glNewList(1,GL_COMPILE); 
   glVertex3f(v1); 
glEndList();
glNewList(2,GL_COMPILE); 
   glVertex3f(v2); 
glEndList();
glNewList(3,GL_COMPILE); 
   glVertex3f(v3); 
glEndList();

glNewList(4,GL_COMPILE);
   glBegin(GL_POLYGON);
      glCallList(1); 
      glCallList(2); 
      glCallList(3);
   glEnd();
glEndList();

To render the polygon, call display list number 4. To edit a vertex, you need only recreate the single display list corresponding to that vertex. Since an index number uniquely identifies a display list, creating one with the same index as an existing one automatically deletes the old one. Keep in mind that this technique doesn't necessarily provide optimal memory usage or peak performance, but it's acceptable and useful in some cases.

OpenGL Programming Guide