#include<gl/glut.h>
#include<math.h>
#include<windows.h>
#include<vector>
#include<algorithm>
using namespace std;
struct Point
{
  int x, y;
  Point(){};
  Point(int tx, int ty)
  {
    x = tx;
    y = ty;
  }
};
vector<Point> p;
double getRatio(double t,double a,double b,double c,double d)
{
  return a * pow(t, 3) + b * pow(t, 2) + c * t + d;
}
void Bezier()
{
  int n = 500;
  double derta = 1.0 / n;
  glPointSize(2);
  glColor3d(0, 0, 0);
  glBegin(GL_POINTS);
  for (int i = 1; i < n; i++)
  {
    double t = derta * i;
    double ratio[4];
    ratio[0] = getRatio(t, -1, 3, -3, 1);
    ratio[1] = getRatio(t, 3, -6, 3, 0);
    ratio[2] = getRatio(t, -3, 3, 0, 0);
    ratio[3] = getRatio(t, 1, 0, 0, 0);
    double x=0, y=0;
    for (int j = 0; j < 4; j++)
    {
      x += ratio[j] * p[j].x;
      y += ratio[j] * p[j].y;
    }
    glVertex2d(x, y);
  }
  glEnd();
}
void myDisplay()
{
  glClear(GL_COLOR_BUFFER_BIT);  //清除顏色緩存和深度緩存

  //畫點
  glPointSize(5);
  glColor3d(1, 0, 0);
  glBegin(GL_POINTS);
  for (int i = 0; i < p.size(); i++)
    glVertex2d(p[i].x, p[i].y);
  glEnd();

  //畫線
  glLineWidth(2);
  glColor3d(0, 1, 0);
  glBegin(GL_LINE_STRIP);
  for (int i = 0; i < p.size(); i++)
    glVertex2d(p[i].x, p[i].y);
  glEnd();

  if (p.size() == 4)
    Bezier();

  glFlush();
}
void mouse(int button, int state, int x, int y)
{
  if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN && p.size() < 4)
  {
    Point t(x, y);
    p.push_back(t);
    glutPostRedisplay();
  }
}

void Reshape(int w, int h)   //兩個參數(shù)：窗口被移動后大小
{
  glViewport(0, 0, w, h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluOrtho2D(0, w, h, 0);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}

void initWindow(int &argc, char *argv[], int width, int height, char *title)  //初始化并顯示到屏幕中央
{
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
  glutInitWindowPosition((GetSystemMetrics(SM_CXSCREEN) - width) >> 1, (GetSystemMetrics(SM_CYSCREEN) - height) >> 1);    //指定窗口位置
  glutInitWindowSize(width, height);    //指定窗口大小
  glutCreateWindow(title);

  glClearColor(1, 1, 1, 0);
  glShadeModel(GL_FLAT);
}

int main(int argc, char *argv[])
{
  initWindow(argc, argv, 600, 600, "四點畫Bezier曲線");

  puts("\n\t鼠標在窗口點擊四次后自動繪制出Bezier曲線");

  glutDisplayFunc(myDisplay);
  glutReshapeFunc(Reshape);
  glutMouseFunc(mouse);

  glutMainLoop();
  return 0;
}