下面这段红宝书中的代码，我试到vc++的环境中编译，debug，发现断点设在main函数的任何一个部分都没有用，
停不下来。只有设在torus中才能停下来。
后来发现，第一次显示的时候并没有经过main和其他函数，只经过了torus和GLuint theTorus;这条语句，也就是编译
链接完了之后初次的显示就被确定了。但是后来有键盘响应的时候，又进入了keyboard和display函数，说明main包括init被
编译没了，一进来就有一次显示，后来的还和一般的程序相同。
不知道我理解的对不对。
/*
* 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;
}
