一个旋转的正方体，为什么红色的面没有显示
#include <gl/glut.h>GLfloat vertices[][3] = {{-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}};GLfloat colors[][3] = {{1.0, 0.0, 0.0}, {0.0, 1.0, 1.0}, {1.0, 1.0, 0.0}, {0.0, 1.0, 0.0}, {0.0, 0.0, 1.0}, {1.0, 0.0, 1.0}};int axis;float theta[3];void polygon(int a, int b, int c, int d){ glBegin(GL_POLYGON); glVertex3fv(vertices[a]); glVertex3fv(vertices[b]); glVertex3fv(vertices[c]); glVertex3fv(vertices[d]); glEnd();}void colorcube(){ glColor3fv(colors[0]); polygon(0, 3, 2, 1); glColor3fv(colors[1]); polygon(2, 3, 7, 6); glColor3fv(colors[2]); polygon(3, 0, 4, 7); glColor3fv(colors[3]); polygon(1, 2, 6, 5); glColor3fv(colors[4]); polygon(4, 5, 6, 7); glColor3fv(colors[5]); polygon(5, 4, 0, 1);}void spinCube(){ theta[axis] += 1.0; if (theta[axis] > 360.0) theta[axis] -= 360.0; glutPostRedisplay();}void mouse(int btn, int state, int x, int y){ if (btn == GLUT_LEFT_BUTTON && state == GLUT_DOWN) axis = 0; if (btn == GLUT_MIDDLE_BUTTON && state == GLUT_DOWN)axis = 1; if (btn == GLUT_RIGHT_BUTTON && state == GLUT_DOWN) axis = 2;}void init(){ //glClearColor(0.0, 0.0, 0.0, 0.0); //glColor3f(1.0, 1.0, 1.0);}void display(void){ glClear(GL_COLOR_BUFFER_BIT); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); gluLookAt(1.0, 1.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0); glLoadIdentity(); glRotatef(theta[0], 1.0, 0.0, 0.0); glRotatef(theta[1], 0.0, 1.0, 0.0); glRotatef(theta[2], 0.0, 0.0, 1.0); colorcube(); glFlush(); glutSwapBuffers();}void reshape(int w, int h){ glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(-4.0, 4.0, -4.0, 4.0, -4.0, 4.0);}int main(int argc, char **argv){ glutInit(&argc, argv); glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB); glutInitWindowSize(400, 400); glutInitWindowPosition(200, 200); glutCreateWindow("OpenGL"); glutDisplayFunc(display); glutReshapeFunc(reshape); glutIdleFunc(spinCube); glutMouseFunc(mouse); init(); glutMainLoop();}