bezier.cpp

#include <GL/glut.h>
#include <math.h>
#include <bits/stdc++.h>

// Point class to keep it a little cleaner.
class Point {
public:
    float x, y;
    void setxy(float x2, float y2) { x = x2; y = y2; }
    const Point & operator=(const Point &rPoint) {
         x = rPoint.x;
         y = rPoint.y;         
         return *this;
      }

};

Point abc[4];

void myInit() {
    glClearColor(0.0,0.0,0.0,0.0);
    glColor3f(1.0,0.0,0.0);
    glPointSize(8.0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0.0,64.0,0.0,48.0);
}

void drawDot(int x, int y) {
    glBegin(GL_POINTS);
    glVertex2i(x,y);
    glEnd();
    glFlush();
}

void drawLine(Point p1, Point p2) {
    glBegin(GL_LINES);
    glVertex2f(p1.x, p1.y);
    glVertex2f(p2.x, p2.y);
    glEnd();
    glFlush();
}

// Calculate the next bezier point.
Point drawBezier(Point A, Point B, Point C, Point D, double t) {
    Point P;
    P.x = pow((1 - t), 3) * A.x + 3 * t * pow((1 -t), 2) * B.x + 3 * (1-t) * pow(t, 2)* C.x + pow (t, 3)* D.x;
    P.y = pow((1 - t), 3) * A.y + 3 * t * pow((1 -t), 2) * B.y + 3 * (1-t) * pow(t, 2)* C.y + pow (t, 3)* D.y;       
    return P;
}

void myDisplay() {
    glClear(GL_COLOR_BUFFER_BIT);    
    Point POld=abc[0];
    abc[0].x=0,abc[0].y=0;
    abc[1].x=5,abc[1].y=9;
    abc[2].x=20,abc[2].y=10;
    abc[3].x=10,abc[3].y=30;
    glColor3f(1.0,0.0,0.0);
    for(int i=0;i<4;i++)
        drawDot(abc[i].x, abc[i].y);        
    glColor3f(1.0,1.0,1.0);
    drawLine(abc[0], abc[1]);
    drawLine(abc[1], abc[2]);
    drawLine(abc[2], abc[3]);    
    for(double t = 0.0;t <= 1.0; t += 0.1) {
        Point P = drawBezier(abc[0], abc[1], abc[2], abc[3],  t);
        drawLine(POld, P);
        POld = P;        
    }
    glFlush();
}

int main(int argc, char *argv[]) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
    glutInitWindowSize(640,480);
    glutInitWindowPosition(100,150);
    glutCreateWindow("Bezier Curve");    
    glutDisplayFunc(myDisplay);
    myInit();
    glutMainLoop();
    return 0;
}