#include <math.h>

#include <gl/glut.h>

#include <iostream>

using namespace std;

struct  Point2

{

    double x;

    double y;

    Point2(int px, int py) { x = px; y = py; }

};

Point2 P0(, );

Point2 P1(, );

Point2 derP0(, );

Point2 derP1(, );

bool mouseLeftDown = false;

bool mouseRightDown = false;

/*计算Hermite曲线*/

void Hermit(int n)

{

    float f1, f2, f3, f4;

    double deltaT = 1.0 / n;

    glBegin(GL_LINE_STRIP);

    for (int i = ; i <= n; i++) {

        double T = i * deltaT;

        f1 = 2.0*pow(T, ) - 3.0*pow(T, ) + 1.0;

        f2 = -2.0*pow(T, ) + 3.0*pow(T, );

        f3 = pow(T, ) - 2.0*pow(T, ) + T;

        f4 = pow(T, ) - pow(T, );

        glVertex2f(f1*P0.x + f2*P1.x + f3*derP0.x + f4*derP1.x,

            f1*P0.y + f2*P1.y + f3*derP0.y + f4*derP1.y);

    }

    glEnd();

}

/*用鼠标进行绘制，完成后可改变控制点，拖动即可*/

void display() {

    glClear(GL_COLOR_BUFFER_BIT);

    glLineWidth(1.5);

    glColor3f(1.0, 0.0, 0.0);

    glBegin(GL_LINES);

    glVertex2f(P0.x, P0.y);

    glVertex2f(P0.x + derP0.x / , P0.y + derP0.y / );

    glVertex2f(P1.x, P1.y);

    glVertex2f(P1.x - derP1.x / , P1.y - derP1.y / );

    glEnd();

    glColor3f(0.0, 0.0, 1.0);

    glPointSize(10.0f);

    glBegin(GL_POINTS);

    glVertex2f(P0.x, P0.y);

    glVertex2f(P0.x + derP0.x / , P0.y + derP0.y / );

    glVertex2f(P1.x, P1.y);

    glVertex2f(P1.x - derP1.x / , P1.y - derP1.y / );

    glEnd();

    Hermit();

    glFlush();

    glutSwapBuffers();

}

void init()

{

    glClearColor(1.0, 1.0, 1.0, 0.0);

    glShadeModel(GL_FLAT);

}

void myReshape(int w, int h)

{

    glViewport(, , (GLsizei)w, (GLsizei)h);

    glMatrixMode(GL_PROJECTION);

    glLoadIdentity();

    gluOrtho2D(0.0, (GLsizei)w, (GLsizei)h, 0.0);

    glMatrixMode(GL_MODELVIEW);

    glLoadIdentity();

}

void mouse(int button, int state, int x, int y)

{

    if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN)

    {

        mouseLeftDown = true;

    }

    if (button == GLUT_LEFT_BUTTON && state == GLUT_UP)

    {

        mouseLeftDown = false;

    }

    if (button == GLUT_RIGHT_BUTTON && state == GLUT_DOWN)

    {

        mouseRightDown = true;

    }

    if (button == GLUT_RIGHT_BUTTON && state == GLUT_UP)

    {

        mouseRightDown = false;

    }

}

double distance(int x1, int y1, int x2, int y2)

{

    return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));

}

void motion(int x, int y)

{

    if (mouseLeftDown)

    {

        if (distance(P0.x + derP0.x / , P0.y + derP0.y / , x, y) < )

        {

            derP0.x = (x - P0.x) * ;

            derP0.y = (y - P0.y) * ;

        }

        if (distance(P1.x - derP1.x / , P1.y - derP1.y / , x, y) < )

        {

            derP1.x = (P1.x - x) * ;

            derP1.y = (P1.y - y) * ;

        }

    }

    glutPostRedisplay();

}

int  main(int argc, char** argv)

{

    glutInit(&argc, argv);

    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);

    glutInitWindowSize(, );

    glutInitWindowPosition(, );

    glutCreateWindow("hello");

    init();

    glutDisplayFunc(display);

    glutReshapeFunc(myReshape);

    glutMouseFunc(mouse);

    glutMotionFunc(motion);

    glutMainLoop();

    return ;

}