DISPLAY LISTS

A display list is a cache of commands.
-- once created, it cannot be modified.
-- E.g., if a definition in a display list uses an integer variable xval, then only the current value of xval is stored. Subsequent changes to xval has no effect on the display list>
-- the list resides with the graphics Server, which may speed up performance over a network.
-- only certain commands can be stored in the display list. E.g., glGet*() and glFlush() are not.

To define a display list:

#define MY_OBJECT_ID 1
glNewList(MY_OBJECT_ID, GL_COMPILE);     glBegin(GL_POLYGON);         glVertex3f(0.0,0.0,0.0);         glVertex3f(1.0,0.0,0.0);         glVertex3f(0.0,1.0,0.0);         glVertex3f(1.0,1.0,0.0);     glEnd(); glEndList();

The option GL_COMPILE says do not immediately execute.

To execute the display list:

glCallList(MY_OBJECT_ID);

You can iterate and do matrix transformations inside the display list:

buildCircle(GLint id) {     GLint i;     GLfloat cosine, sine;     glNewList(id, GL_COMPILE);       glBegin(GL_POLYGON);
for(i=0; i<100; i++){           cosine = cos(i*2*PI/100.0);           sine = sin(i*2*PI/100.0);           glVertex2f(cosine,sine);         }
glEnd();
glTranslatef(2.0, 0.0, 0.0);
glEndList(); }

E.G., to draw a row of 99 touching circles:

buildCircle(MY_CIRCLE_ID); for (i=0; i<99; i++)       glCallList(MY_CIRCLE_ID);

Display lists cannot be nested.
But you can have Hierarchical Display Lists in which a display list calls other display lists.
-- E.g., to construct a complex object with many parts.

glNewList(BIKE_ID, GL_COMPILE);       glCallList(bicycleFrame);       glTranslatef(1.0, 0.0, 0.0);       glCallList(Wheel);       glTranslatef(3.0, 0.0, 0.0);       glCallList(Wheel); glEndList();

To avoid the OpenGL state outside the display list to be affected by the list,
-- use glPushMatrix()/glPopMatrix()
-- and glPushAttrib()/glPopAttrib().

Automatic management of display list indices:

• GLuint glGetLists(GLsizei range)
  generates a range of unused index.
• GLboolean glIsList(GLuint list)
  determines if an index is used.
• GLvoid glDeleteLists(GLuint list, GLsizei range)
  deletes a range of lists

Executing Multiple Display Lists
-- put the list indices into an array and call glCallLists().
-- E.g., to display a string of letters.
-- glListBase() is also useful (it specifies an offset for indices).