连接的三角形未显示

Question

我尝试使用GL_TRIANGLE_STRIP原语常量绘制一个多边形（使用OpenGL库和C ++）作为一组连接的三角形。我写的代码就像

#include <GL/glut.h>
void init()
{
    glClearColor(1.0,1.0,1.0,0.0);
    glMatrixMode(GL_PROJECTION);
    gluOrtho2D(0.0,300.0,0.0,250.0);
}
void polygonDrawing()
{
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1.0,0.0,0.0);
    int point1[] = {30,80};
    int point2[] = {80,40};
    int point3[] = {120,40};
    int point4[] = {165,80};
    int point5[] = {120,120};
    int point6[] = {80,120};

    glBegin(GL_TRIANGLE_STRIP);
            glVertex2iv(point1);
            glVertex2iv(point2);
            glVertex2iv(point6);
            glVertex2iv(point3);
            glVertex2iv(point5);
            glVertex2iv(point4);
    glEnd();

    glFlush();
}
int main(int argc,char** argv)
{
    glutInit(&argc,argv);
    glutInitWindowSize(300,300);
    glutInitWindowPosition(150,100);
    glutCreateWindow("An OpenGl window for a polygon");

    init();

    glutDisplayFunc(polygonDrawing);
    glutMainLoop();
    return 0;
}

我的问题是：代码正确显示多边形，但不显示其中的连接三角形。任何人都可以告诉我为什么会这样，以及如何克服它？