OpenGL小问题

// goldQuad.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include<windows.h>
#include<gl/Gl.h>
#include<gl/glu.h>
#include<gl/glut.h>
#include<time.h>

const int screenWidth=640,screenHeight=480;
const double PC=1.618033989;
double width;
bool selected=false;
int spin=0;
GLint numcount=0;

struct GLdoublePoint{
double x,y;
};

GLdoublePoint T[4];

void myInit(void){

glClearColor(1.0,1.0,1.0,0.0);
glPointSize(3.0);
glColor3f(0.0f,0.0f,0.0f);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0,(GLdouble)screenWidth,0.0,(GLdouble)screenHeight);
}

void drawQuad(void){
glBegin(GL_LINE_LOOP);
glVertex2d(T[0].x,T[0].y);
glVertex2d(T[2].x,T[2].y);
glVertex2d(T[1].x,T[1].y);

glVertex2d(T[3].x,T[3].y);
glEnd();
glFlush();