繪製地球，月亮，太陽 之間的運動關係

#include <GL/glut.h>
#include <math.h>

#define PI 3.1415926535f
#define A 0.31415926535f
#define B 0.31415926535f

// 360 days
// 30 days
static int day = 0;
static int interval = 10;
struct MyPoint
{
	float x, y, z;
};

void drawBall(float R, float red, float green, float blue)
{
	MyPoint pts[11][20];
	for (int i = 0; i <= PI / A; ++i)
	{
		float y = cosf(A*i) * R;
		float t = sinf(A*i) * R;

		for (int j = 0; j < PI / B * 2; ++j)
		{
			float x = t * cosf(j*B);
			float z = t * sinf(j*B);

			pts[i][j].x = x;
			pts[i][j].y = y;
			pts[i][j].z = z;
		}
	}
	glEnable(GL_CULL_FACE);
	glCullFace(GL_BACK);
	//	glPolygonMode(GL_BACK, GL_LINE);
	glPolygonMode(GL_FRONT, GL_LINE);

	glBegin(GL_QUADS);
	glColor3f(red, green, blue);
	for (int i = 0; i < PI / A; ++i)
	{
		for (int j = 0; j < PI / B * 2; ++j)
		{
			glVertex3f(pts[i][j].x, pts[i][j].y, pts[i][j].z);
			glVertex3f(pts[i + 1][j].x, pts[i + 1][j].y, pts[i + 1][j].z);
			glVertex3f(pts[i + 1][(j + 1) % 20].x, pts[i + 1][(j + 1) % 20].y, pts[i + 1][(j + 1) % 20].z);
			glVertex3f(pts[i][(j + 1) % 20].x, pts[i][(j + 1) % 20].y, pts[i][(j + 1) % 20].z);
		}
	}
	glEnd();

}

// 使用OpenGL的接口，來繪製
static void display()
{
	glClear(GL_COLOR_BUFFER_BIT);

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity(); // 初始化，清空
	gluPerspective(60, 1, 0.1f, 10.0f);

	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	gluLookAt(0, 1, 1, 0, 0, 0, 0, 1, 0);

	// 繪製太陽
	drawBall(0.1f, 1.0f, 0, 0);
	// 繪製地球時，應該物體挪到
	
	glRotatef(day, 0, 1, 0);
	glTranslatef(0.2f, 0, 0);
	
	// 繪製地球
	drawBall(0.05f, 0, 0, 1.0f);

	// day的範圍是0-360， 每30天繞地球一圈
	glRotatef(day % 30* 360 / 30, 0, 1, 0);
	glTranslatef(0.1f, 0, 0);
	// 繪製月亮
	drawBall(0.025f, 1.0f, 1.0f, 0);

	glFlush();
}

static void timer_func(int)
{
	day++;
	if (day == 360) day = 0;
	glutTimerFunc(interval, timer_func, 0);
	glutPostRedisplay();
}

int main(int argc, char*argv[])
{
	// 初始化環境
	glutInit(&argc, argv);

	// 創建一個窗口, 參數的參照物是系統桌面的左上角
	glutInitWindowPosition(100, 100);
	glutInitWindowSize(400, 400);
	glutCreateWindow("Hello OpenGL");

	// 設置顯示函數
	glutDisplayFunc(display);


	glutTimerFunc(interval, timer_func, 0);

	// 進入主循環
	glutMainLoop();

	return 0;
}