glFrontFace(GL_CCW);   // 设置CCW方向为“正面”，CCW即CounterClockWise，逆时针
glFrontFace(GL_CW);    // 设置CW方向为“正面”，CW即ClockWise，顺时针

#include <GL/glut.h>

#include <math.h>
void myDisplay(void)
{
    glClear(GL_COLOR_BUFFER_BIT);
    glPolygonMode(GL_FRONT, GL_FILL); // 设置正面为填充模式
    glPolygonMode(GL_BACK, GL_LINE);   // 设置反面为线形模式
    glFrontFace(GL_CCW);               // 设置逆时针方向为正面

    glBegin(GL_POLYGON);               // 按逆时针绘制一个正方形，在左下方
    glVertex2f(-0.5f, -0.5f);
    glVertex2f(0.0f, -0.5f);
    glVertex2f(0.0f, 0.0f);
    glVertex2f(-0.5f, 0.0f);
    glEnd();

    glBegin(GL_POLYGON);               // 按顺时针绘制一个正方形，在右上方
    glVertex2f(0.0f, 0.0f);
    glVertex2f(0.0f, 0.5f);
    glVertex2f(0.5f, 0.5f);
    glVertex2f(0.5f, 0.0f);
    glEnd();

    glFlush();
}

int main(int argc, char* argv[])
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
    glutInitWindowPosition(100, 100);
    glutInitWindowSize(400, 400);
    glutCreateWindow("第一个OpenGL程序");
    glutDisplayFunc(&myDisplay);
    glutMainLoop();

    return 0;
}

点的

void myDisplay(void)
{
    glClear(GL_COLOR_BUFFER_BIT);
    glPointSize(5.0f);
    glBegin(GL_POINTS);
    glVertex2f(0.0f, 0.0f);
    glVertex2f(0.5f, 0.5f);
    glEnd();
    glFlush();
}

直线

void myDisplay(void)
{
    glClear(GL_COLOR_BUFFER_BIT);
    glEnable(GL_LINE_STIPPLE);
    glLineStipple(2, 0x0F0F);
    glLineWidth(10.0f);
    glBegin(GL_LINES);
    glVertex2f(0.0f, 0.0f);
    glVertex2f(0.5f, 0.5f);
    glEnd();
    glFlush();
}