#include <windows.h>
#include <gl/glut.h>
#include <math.h>

const double PI=3.1415926;
const float MIN_LEN = 0.0001;
const float LEN = 0.6;
const float g_x1=-LEN, g_y1=-LEN, g_x2=0, g_y2=LEN, g_x3=LEN, g_y3=-LEN;

/// 窗口寬度
int g_width=400;

/// 窗口高度
int g_height=300;

///鼠標器左鍵是否按下
bool mouse_button_pressed=false;    

///記錄鼠標器位置
int mouse_x;                        

///記錄鼠標器位置
int mouse_y;                        

///旋轉的緯度
float theta=0;                     

///旋轉的經度
float phi=0;                       


/**
鼠標按鈕回調函數
*/
void mouse(int button, int state, int x, int y)
{
    if(button == GLUT_LEFT_BUTTON)
    {
        if(state == GLUT_DOWN)
            //如果鼠標器左鍵按下，mouse_button_pressed置位
            //并記錄光標位置
        {
            mouse_button_pressed = true;
            mouse_x = x;
            mouse_y = y;
        }
        else
        {
            mouse_button_pressed = false;
        }
    }
}

/**
鼠標運動處理函數
*/
void motion(int x, int y)
{
    if(mouse_button_pressed)
    {
        theta -= y-mouse_y;     //根據鼠標器的移動改變旋轉的緯度
        if(theta<0) theta = 0;  //限制緯度在0到180度之間
        if(theta>180) theta = 180;

        phi += x-mouse_x;       //根據鼠標器的移動改變旋轉的經度
        if(phi<0) phi+=360;     //限制經度在0到360度之間
        if(phi>360) phi-=360;

        mouse_x = x;    //更新記錄的鼠標器位置
        mouse_y = y;

        glutPostRedisplay();
            //通知系統：窗口需要刷新
    }
}



/**
點類
*/
class point {

public:
	float x;
	float y;
public:
	point(float _x, float _y)  {x=_x;y=_y;}
	point(point& p)  {x=p.x; y=p.y;}
	point middle(point& p2) {return point((x+p2.x)/2, (y+p2.y)/2);}
        float between(point& p2) {return (x-p2.x)*(x-p2.x)+(y-p2.y)*(y-p2.y);}
};


/**
繪制Seripinski墊票
三點坐標為a(x1,y1), b(x2,y2), c(x3,y3)
*/

void seripinski(point& a, point& b, point& c)
{
   if (a.between(b) < MIN_LEN && b.between(c) < MIN_LEN) return;

   //繪制三角形
   glBegin(GL_LINE_LOOP);
   glVertex2f(a.x, a.y);
   glVertex2f(b.x, b.y);
   glVertex2f(c.x, c.y);
   glEnd();
   
   //遞歸繪制三個角
   seripinski(a, a.middle(b), a.middle(c));
   seripinski(a.middle(b), b, b.middle(c));
   seripinski(a.middle(c), b.middle(c), c);
}

/**
\b 主處理回調函數,每當需要重畫時由OpenGL庫調用
\b 該函數功能是調用seripinski,繪制seripinski墊票
\b 三點坐標分別為a(10, g_height-10),b(g_width/2,g_height-10),c(g_width-10, 10)
*/
void main_display_loop(void)
{
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); //刷新背景 

  glMatrixMode (GL_PROJECTION);   //設置矩陣模式為投影矩陣
  glLoadIdentity();               //初始化投影矩陣
  glOrtho(-1,1,-1,1,-1,1);        //設置平行投影的投影矩陣


  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
  glRotatef(phi,0,1,0);       //繞y軸旋轉OCS，旋轉的角度為phi
  glRotatef(theta,1,0,0);     //繞x軸旋轉OCS，旋轉的角度為theta


  glColor3f(1, 0, 0);
  glPushMatrix();
  glTranslatef(0, 0, -0.4);
  seripinski(point(g_x1, g_y1), point(g_x2, g_y2), point(g_x3, g_y3));
  glPopMatrix();

  glColor3f(0, 1, 0);
  glPushMatrix();
  glTranslatef(0, 0, 0.4);
  seripinski(point(g_x1, g_y1), point(g_x2, g_y2), point(g_x3, g_y3));
  glPopMatrix();

  glColor3f(0, 0, 1);
  glPushMatrix();
  glTranslatef(0.4, 0, 0);
  glRotatef(90, 0, 1, 0);
  seripinski(point(g_x1, g_y1), point(g_x2, g_y2), point(g_x3, g_y3));
  glPopMatrix();

  glColor3f(0, 0.3, 0.5);
  glPushMatrix();
  glTranslatef(-0.4, 0, 0);
  glRotatef(90, 0, 1, 0);
  seripinski(point(g_x1, g_y1), point(g_x2, g_y2), point(g_x3, g_y3));
  glPopMatrix();


  glFlush(); 	  //更新窗口 

  glutSwapBuffers();
}

/**
OPENGL 特性初始化函數
*/
init()
{
  glEnable(GL_DEPTH_TEST);
  glDepthFunc(GL_LESS);

  glClearColor(0,0,0,1); 
  glClearDepth(1);
  glColor3f(0, 0, 1);
}

/// 主函數
int main(int argc, char* argv[])
{
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE| GLUT_RGBA);
  glutInitWindowSize(g_width, g_height);
  glutCreateWindow("OpenGL");
  init();
  glutMouseFunc(mouse);
  glutMotionFunc(motion);
  glutDisplayFunc(main_display_loop);
  glutMainLoop();
  return 0;
}