Display Lists
Display lists were a means of compiling a list
of OpenGL instructions and executing them at a later date. They
were arguably not a means of vertex specification, specifically (pun
intended) but were often used to improve the speed of doing so. They
are covered here for the sake of completeness.
#include <assert.h>
#include <GL/glut.h>
#include <GL/glext.h>
static int list;
static void
reshape(int width, int height)
{
glViewport(0, 0, width, height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, width, 0, height, -1.0, 100.0);
assert(glGetError() == GL_NO_ERROR);
}
static void
init(void)
{
list = glGenLists(1);
glNewList(list, GL_COMPILE);
glBegin(GL_TRIANGLES);
glColor3d(100.0, 0.0, 0.0);
glVertex3d(0.0, 0.0, 0.0);
glColor3d(0.0, 100.0, 0.0);
glVertex3d(100.0, 0.0, 0.0);
glColor3d(0.0, 0.0, 100.0);
glVertex3d(100.0, 100.0, 0.0);
glEnd();
glEndList();
}
static void
display(void)
{
glClearColor(0.3f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glPushMatrix();
glTranslated(20.0, 20.0, 0.0);
glCallList(list);
glTranslated(120.0, 120.0, 0.0);
glCallList(list);
glPopMatrix();
glutSwapBuffers();
}
int
main(int argc, char **argv)
{
glutInit(&argc, argv);
glutCreateWindow("Display list triangle");
init();
glutReshapeFunc(reshape);
glutDisplayFunc(display);
glutIdleFunc(glutPostRedisplay);
glutMainLoop();
return 0;
}
As can be seen from the output, the triangle drawing commands
are compiled into a display list and then called twice to draw
two triangles. The commands in the display list were typically
stored in the OpenGL implementation's memory in order to reduce
the number of commands sent between the program and the
OpenGL driver. Display lists were obviously not a solution to
the general inefficiencies of the immediate mode.
