Hi,
I was playing around with glGenLists(), I wrote a minimal example to test the return value of glGenLists(); however, I did not get the expected result as the book claimed. The return value of glGenLists() should be 1 when it succeeds and 0 when it fails.
This is my code:
#include <string>
#include <iostream>
#include <cstdio>
#include <GL/glut.h>
using namespace std;
string getOpenGLErrorMessage( GLenum error ) {
switch( error ) {
case GL_NO_ERROR:
return "GL_NO_ERROR";
case GL_INVALID_ENUM:
return "GL_INVALID_ENUM";
case GL_INVALID_VALUE:
return "GL_INVALID_VALUE";
case GL_INVALID_OPERATION:
return "GL_INVALID_OPERATION";
case GL_STACK_OVERFLOW:
return "GL_STACK_OVERFLOW";
case GL_STACK_UNDERFLOW:
return "GL_STACK_UNDERFLOW";
case GL_OUT_OF_MEMORY:
return "GL_OUT_OF_MEMORY";
}
}
int main() {
int index = glGenLists( 5 );
cout << index << '
';
GLenum error = glGetError();
cout << getOpenGLErrorMessage( error ) << endl;
glNewList( index, GL_COMPILE );
glVertex3f( 0.0, 0.0, 0.0 );
glEndList();
}
Next, I compare my code example with the code from the book (The Red Book)
/*
* torus.c
* This program demonstrates the creation of a display list.
*/
#include <GL/glut.h>
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#define PI_ 3.14159265358979323846
GLuint theTorus;
/* Draw a torus */
static void torus(int numc, int numt)
{
int i, j, k;
double s, t, x, y, z, twopi;
twopi = 2 * PI_;
for (i = 0; i < numc; i++) {
glBegin(GL_QUAD_STRIP);
for (j = 0; j <= numt; j++) {
for (k = 1; k >= 0; k--) {
s = (i + k) % numc + 0.5;
t = j % numt;
x = (1+.1*cos(s*twopi/numc))*cos(t*twopi/numt);
y = (1+.1*cos(s*twopi/numc))*sin(t*twopi/numt);
z = .1 * sin(s * twopi / numc);
glVertex3f(x, y, z);
}
}
glEnd();
}
}
/* Create display list with Torus and initialize state */
static void init(void)
{
theTorus = glGenLists (1);
glNewList(theTorus, GL_COMPILE);
torus(8, 25);
glEndList();
glShadeModel(GL_FLAT);
glClearColor(0.0, 0.0, 0.0, 0.0);
}
/* Clear window and draw torus */
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glColor3f (1.0, 1.0, 1.0);
glCallList(theTorus);
glFlush();
}
/* Handle window resize */
void reshape(int w, int h)
{
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(30, (GLfloat) w/(GLfloat) h, 1.0, 100.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0, 0, 10, 0, 0, 0, 0, 1, 0);
}
/* Rotate about x-axis when "x" typed; rotate about y-axis
when "y" typed; "i" returns torus to original view */
void keyboard(unsigned char key, int x, int y)
{
switch (key) {
case 'x':
case 'X':
glRotatef(30.,1.0,0.0,0.0);
glutPostRedisplay();
break;
case 'y':
case 'Y':
glRotatef(30.,0.0,1.0,0.0);
glutPostRedisplay();
break;
case 'i':
case 'I':
glLoadIdentity();
gluLookAt(0, 0, 10, 0, 0, 0, 0, 1, 0);
glutPostRedisplay();
break;
case 27:
exit(0);
break;
}
}
int main(int argc, char **argv)
{
glutInitWindowSize(200, 200);
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutCreateWindow(argv[0]);
init();
glutReshapeFunc(reshape);
glutKeyboardFunc(keyboard);
glutDisplayFunc(display);
glutMainLoop();
return 0;
}
The output of glGenLists() in this example was 1 as expected. When looking at this code and comparing it with mine, I don’t see any difference. The first four subroutines are:
- glutInitWindowSize(200, 200);
- glutInit(&argc, argv);
- glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
- glutCreateWindow(argv[0]);
which come from glut not openGL. Hence the first openGL call to openGL must be init() which in turn called glGenLists(). Apparently, mine above code did exactly the same. So I guess my question is, is there any constraint on using glGenLists?
Thank you