• So Far:
  • We have executed all OpenGL "commands" in immediate mode
• A Drawback:
  • Many of the same operations are performed multiple times for no reason
• A Solution:
  • Cache "commands" in a display list

• Geometry:
  • For static presentations we might want to use the same "shape" multiple times (e.g., the wheels on a car)
  • For animations we might want to cache the entire "shape" and just transform it for each frame
• Matrix Operations:
  • Both computed matrices and inverses can be stored in display lists
• Remote Execution:
  • When using a remote server, display lists (which are part of the server state) are stored on the server and hence need not be re-transmitted

• Name the display list
• Create the display list

• Transform, set material properties, etc.. as needed
• Execute the display list

• The Function:
  • GLuint glGenLists(GLsizei range)
• Argument:
  • The number of (contiguous) display lists to "name"
• Return:
  • The index of the first display list (or 0 if there are too few unallocated display lists available)

openglexamples/displaylists/teapots.c (Fragment: name)

        
static GLuint  teapot; // For a display list
        

• The Functions:
  • void glNewList(GLuint name, GLenum mode) specifies the start of list with index name
  • void glEndList() specifies the end
• Modes:
  • GL_COMPILE or GL_COMPILE_AND_EXECUTE

openglexamples/displaylists/teapots.c (Fragment: create)

        
  // Create the display list
  glNewList(teapot, GL_COMPILE);
  glutSolidTeapot(0.2);
  glEndList();
        

• Commands that retrieve state information
• Commands that set client state

• The Functions:
  • void glCallList(GLuint name)
• Scope:
  • Can be called from anywhere, as long as the OpenGL context that can access the display list is active

openglexamples/displaylists/teapots.c (Fragment: use)

        
  // Use the display list
  for (int i = 0; i < numTeapots; i++) {
    glLoadIdentity();
    glTranslatef(deltaX[i], deltaY[0], 0.0);
    glMaterialfv(GL_FRONT, GL_SPECULAR, colorBrown);

    // Execute the display list
    glCallList(teapot);
  }
        

• An Observation:
  • glCallList() can be called between calls to glNewList() and glEndList()
• Implication:
  • Display lists can contain other display lists [normally up to a depth of 64; see void glGetIntegerv(GL_MAX_LIST_NESTING, GLint *depth ]
• Common Uses:
  • Shapes that are composed of other shapes (e.g., a display list for a hand that contains five executions of a display list for a finger)

• Specifying the Offset in "Names":
  • void glListBase(GLuint offset)
• Executing:
  • void glCallLists(GLsizei n, GLenum type, conts GLvoid* lists)
  • where type is usually GL_INT and lists is usually a pointer to an array of GLint "names"