OpenGL - 连续绘制三次B样条曲线

计算公式：

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使用说明：鼠标在窗口点击绘制B样条曲线，鼠标右键移动控制点。退格键（←）删除鼠标所在的点。

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运行效果：

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代码如下：

#include<gl/glut.h>
#include<math.h>
#include<windows.h>
#include<vector>
#include<algorithm>
using namespace std;
bool mouseRightIsDown = false;
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;
}
double caculateSquarDistance(Point a, Point b)
{
    return (a.x - b.x)*(a.x - b.x) + (a.y - b.y)*(a.y - b.y);
}
int getIndexNearByMouse(int x, int y)
{
    double precision = 200;     //精确度
    int index = -1;
    double Min;
    for (int i = 0; i < p.size(); i++)
    {
        double dis = caculateSquarDistance(p[i], Point(x, y));
        if (dis < precision)
        {
            if (index == -1)
            {
                index = i;
                Min = dis;
            }
            else if (dis < Min)
            {
                index = i;
                Min = dis;
            }
        }
    }
    return index;
}
void Bezier(Point a,Point b,Point c,Point d)
{
    int n = 500;
    double derta = 1.0 / n;
    glPointSize(2);
    glColor3d(0, 0, 0);
    glBegin(GL_LINE_STRIP);
    for (int i = 0; i <= n; i++)
    {
        double t = derta * i;
        double ratio[4];
        ratio[0] = getRatio(t, -1, 3, -3, 1);
        ratio[1] = getRatio(t, 3, -6, 0, 4);
        ratio[2] = getRatio(t, -3, 3, 3, 1);
        ratio[3] = getRatio(t, 1, 0, 0, 0);
        double x=0, y=0;
        x += ratio[0] * a.x + ratio[1] * b.x + ratio[2] * c.x + ratio[3] * d.x;
        y += ratio[0] * a.y + ratio[1] * b.y + ratio[2] * c.y + ratio[3] * d.y;
        x /= 6.0;
        y /= 6.0;
        glVertex2d(x, y);
    }
    glEnd();
}
void myDisplay()
{
    glClear(GL_COLOR_BUFFER_BIT);    //清除颜色缓存和深度缓存

    //画点
    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();

    //画线
    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)
    for (int i = 0; i < p.size() - 3; i++)
        Bezier(p[i], p[i + 1], p[i + 2], p[i + 3]);

    glFlush();
}
void keyboard(unsigned char key, int x, int y)
{
    if (key == 27)      //ESC
        exit(0);
    if (key == 8)       //退格键
    {
        int index = getIndexNearByMouse(x, y);
        if (index == -1)
            return;
        p.erase(p.begin() + index);
        glutPostRedisplay();
    }
}
void mouse(int button, int state, int x, int y)
{
    if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN)
    {
        Point t(x, y);
        p.push_back(t);
        glutPostRedisplay();
    }
    if (button == GLUT_RIGHT_BUTTON && state == GLUT_DOWN)
        mouseRightIsDown = true;
    if (button == GLUT_RIGHT_BUTTON && state == GLUT_UP)
        mouseRightIsDown = false;
}
void motion(int x, int y)
{
    if (mouseRightIsDown)       //按住右键移动点
    {
        int index = getIndexNearByMouse(x, y);
        if (index == -1)
            return;
        p[index].x = x;
        p[index].y = y;
        glutPostRedisplay();
    }
}
void Reshape(int w, int h)      //两个参数：窗口被移动后大小
{
    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)    //初始化并显示到屏幕中央
{
    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, 1000, 600, "B样条曲线");

    puts("\n\t鼠标在窗口点击绘制B样条曲线，鼠标右键移动控制点");
    puts("\t退格键（←）删除鼠标所在的点");

    glutDisplayFunc(myDisplay);
    glutReshapeFunc(Reshape);
    glutMouseFunc(mouse);
    glutMotionFunc(motion);
    glutKeyboardFunc(keyboard);

    glutMainLoop();
    return 0;
}