Hi,
I’m trying to determine why my code below does not correctly draw a rotating cube. I specified normals for each of the vertices and enabled GL_CULL_FACE followed by a call to glCullFace(GL_BACK), however I can still see through some polygons. I was thinking that the normal vectors would have to be changed after every rotation, but I don’t know. Although I can get a rotating cube to draw correctly by enabling GL_DEPTH_TEST, I can’t seem to figure out why this way does not work.
Any help would be appreciated.
#include <GL/glut.h>
#include <stdlib.h>
GLdouble spin = 0.0;
static GLfloat vertices[] = {1.0, 1.0, 1.0, -1.0, 1.0, 1.0, -1.0, -1.0, 1.0, 1.0, -1.0, 1.0,
1.0, 1.0, -1.0, -1.0, 1.0, -1.0, -1.0, -1.0, -1.0, 1.0, -1.0, -1.0,
1.0, 1.0, 1.0, 1.0, -1.0, 1.0, 1.0, -1.0, -1.0, 1.0, 1.0, -1.0,
-1.0, -1.0, 1.0, -1.0, -1.0, -1.0, 1.0, -1.0, -1.0, 1.0, -1.0, 1.0,
-1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, -1.0, -1.0, 1.0, -1.0,
-1.0, 1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, 1.0, -1.0, 1.0, 1.0};
static GLfloat colors[] = {1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0,
1.0, 1.0, 0.0, 1.0, 1.0, 0.0, 1.0, 1.0, 0.0, 1.0, 1.0, 0.0,
1.0, 0.0, 1.0, 1.0, 0.0, 1.0, 1.0, 0.0, 1.0, 1.0, 0.0, 1.0,
0.0, 1.0, 1.0, 0.0, 1.0, 1.0, 0.0, 1.0, 1.0, 0.0, 1.0, 1.0,
1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0,
0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0};
static GLfloat normals[] = {0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0,
0.0, 0.0, -1.0, 0.0, 0.0, -1.0, 0.0, 0.0, -1.0, 0.0, 0.0, -1.0,
1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0,
0.0, -1.0, 0.0, 0.0, -1.0, 0.0, 0.0, -1.0, 0.0, 0.0, -1.0, 0.0,
0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
-1.0, 0.0, 0.0, -1.0, 0.0, 0.0, -1.0, 0.0, 0.0, -1.0, 0.0, 0.0};
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity();
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_NORMAL_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, vertices);
glNormalPointer(GL_FLOAT, 0, normals);
glColorPointer(3, GL_FLOAT, 0, colors);
glTranslatef(0.0, 0.0, -100.0);
glRotatef(spin, 1.0, 0.5, 0.8);
glScalef(25.0, 25.0, 25.0);
glBegin(GL_QUADS);
for (int i = 0; i < 24; i = i + 4)
{
glArrayElement(i);
glArrayElement(i+1);
glArrayElement(i+2);
glArrayElement(i+3);
}
glEnd();
glutSwapBuffers();
glFlush();
}
void spin_display()
{
spin = spin + .5;
if (spin > 360.0)
spin = spin - 360;
glutPostRedisplay();
}
void init (void)
{
glClearColor (0.0, 0.0, 0.0, 0.0);
glShadeModel (GL_FLAT);
glEnable(GL_CULL_FACE);
glCullFace(GL_BACK);
}
void reshape (int w, int h)
{
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-50, 50, -50, 50, 5, 1000);
glMatrixMode(GL_MODELVIEW);
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(500, 500);
glutCreateWindow(argv[0]);
init();
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutIdleFunc(spin_display);
glutMainLoop();
return 0;
}