Question

OpenGL 为什么显示不出来图形，只显示出来了背景？求大神指导！

//#define GLUT_DISBALE_ATEXIT_HACK
#define GLUT_DISABLE_ATEXIT_HACK
#include<windows.h>
#include<GL/GL.H>
#include<GL/glut.h>
//#include<GL/GLU.H>
#include<math.h>
#define PI 3.1415926
//清除窗口初始化
void init()
{
glClearColor(0.0f,0.0f,0.0f,0.0f);
glShadeModel(GL_FLAT);

}
/*改变大小*/
void ChangeSize(int w,int h)
{
glViewport(0,0,(GLsizei)w,(GLsizei)h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0,(GLdouble)w,0.0,(GLdouble)h);

}
GLfloat R=0.5f;
//绘制物体
void display()
{
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(1.0f,0.0f,0.0f);
//画坐标轴
glBegin(GL_LINES);
glVertex2f(-1.0f,0.0f);
glVertex2f(1.0f,0.0f);
glVertex2f(0.0f,1.0f);
glVertex2f(0.0f,-1.0f);
glEnd();
//画圆....
glBegin(GL_LINE_LOOP);
for(int i=0;i<=1000;++i)
{
glVertex2f(R*cos(2*PI/1000*i),R*sin(2*PI/1000*i));
}
glEnd();
glFlush();

}
//定义窗口
int main(int argc,char**argv)
{
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
glutInitWindowPosition(200,200);
glutInitWindowSize(300,300);
glutCreateWindow("draw circle");
init();
//glutDisplayFunc(display);
glutReshapeFunc(ChangeSize);
glutDisplayFunc(display);
glutIdleFunc(display);
//glutIdleFunc();
glutMainLoop();
return 0;

}

Answer 1

//#define GLUT_DISBALE_ATEXIT_HACK
#define GLUT_DISABLE_ATEXIT_HACK
#include<windows.h>
#include<GL/GL.H>
#include<GL/glut.h>
//#include<GL/GLU.H>
#include<math.h>
#define PI 3.1415926
//清除窗口初始化
void init()
{
	glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
	glShadeModel(GL_FLAT);

}
/*改变大小*/
void ChangeSize(int w, int h)
{
	glViewport(0, 0, (GLsizei)w, (GLsizei)h);

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	//gluOrtho2D(0.0, (GLdouble)w, 0.0, (GLdouble)h);
	gluPerspective(60, 1, 0.1, 100);	// 设置投影转换

	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	gluLookAt(0, 0, -2, 0, 0, 0, 0, 1, 0);	// 设置视点

}
GLfloat R = 0.5f;
//绘制物体
void display()
{
	glClear(GL_COLOR_BUFFER_BIT);
	glColor3f(1.0f, 0.0f, 0.0f);
	//画坐标轴
	glBegin(GL_LINES);
	glVertex2f(-1.0f, 0.0f);
	glVertex2f(1.0f, 0.0f);
	glVertex2f(0.0f, 1.0f);
	glVertex2f(0.0f, -1.0f);
	glEnd();
	//画圆....
	glBegin(GL_LINE_LOOP);
	for (int i = 0; i <= 1000; ++i)
	{
		glVertex2f(R*cos(2 * PI / 1000 * i), R*sin(2 * PI / 1000 * i));
	}
	glEnd();
	glFlush();

}
//定义窗口
int main(int argc, char**argv)
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
	glutInitWindowPosition(200, 200);
	glutInitWindowSize(300, 300);
	glutCreateWindow("draw circle");
	init();
	//glutDisplayFunc(display);
	glutReshapeFunc(ChangeSize);
	glutDisplayFunc(display);
	glutIdleFunc(display);
	//glutIdleFunc();
	glutMainLoop();
	return 0;

}