opengl问个问题，坐标的问题

[yezj0010]

先发个代码问一下，这个代码我想绘制一个多边形，但是没有显示结果，问一下问题出在哪里？

#include<GL/glut.h>
#include<GL/gl.h>
#include<GL/glu.h>

void init()
{
	glClearColor(0.0,0.0,0.0,0.0);
	glShadeModel(GL_FLAT);
}

void display()
{
	glClear(GL_COLOR_BUFFER_BIT);
	glColor4f(1.0,0.0,0.0,0.0);
	glBegin(GL_POLYGON);
	glVertex2f(-1,-1);
	glVertex2f(-1,1);
	glVertex2f(1,1);
	glVertex2f(1,-1);
	glEnd();
}

void reshape(GLsizei w,GLsizei h)
{
	glViewport(0,0,w,h);
}

int main(int argc, char* argv[])
{
	glutInitDisplayMode(GLUT_RGBA|GLUT_SINGLE);
	glutInitWindowSize(300,300);
	glutCreateWindow("test");
	
	init();
	
	glutReshapeFunc(reshape);
	glutDisplayFunc(display);
	glutMainLoop();
	return 0;
}