why the opengl can't print string - string

Question

#include "stdafx.h"
#include <gl/glut.h>
void resizeEvent(int w, int h)
{
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, w, h, 0);
glMatrixMode(GL_MODELVIEW);
glutPostRedisplay();
}
void displayEvent()
{
glClearColor(1, 1, 1, 0);
glClear(GL_COLOR_BUFFER_BIT);
glutSwapBuffers();
char text[] = "Hello World!";
glRasterPos2d(110, 110);
glColor3f(1, 0, 0);
for(int i=0; text[i] != '\0'; i++)
{
glutBitmapCharacter(GLUT_BITMAP_8_BY_13, text[i]);
}
}
int main(int argc, char *argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(400, 300);
glutInitWindowPosition(0, 0);
glutCreateWindow("Hello");
glutDisplayFunc(displayEvent);
glutReshapeFunc(resizeEvent);
glutMainLoop();
return 0;
}
I learn from a ppt,and think it will print a string.But it does not work .I search from google,but no answer. I don't know why it can't print a string.
if glutBitmapCharacter is wrong ?

Answer 1

All the commands in opengl, renders on the frame buffer only when flush or finish call happens, so all your commands are still in queue and yet to be displayed on frame buffer. You need to call glFlush/glFinish at the end, glut provides glutSwapBuffers, so in the end of your displayEvent function you need to call glutSwapBuffers to see the effect of your displayEvent function.