CG 8 – FLAG USING BEZIER CURVE ALGORITHM

  CG LAB
8. Develop a menu driven program to animate a flag using the Bezier Curve algorithm

#include<GL/glut.h>
#include<math.h>
#include<stdio.h>

void bezierCoefficients(int n,int *c)
{
int k,i;
for(k=0;k<=n;k++)
{
c[k]=1;
for(i=n;i>=k+1;i–)
c[k]*=i;
for(i=n-k;i>=2;i–)
c[k]/=i;
}
}

void display()
{
int cp[4][2]={{10,10},{100,200},{200,50},{300,300}};
int c[4],k,n=3;
float x,y,u,blend;
bezierCoefficients(n,c);
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(1.0,0.0,0.0);
glLineWidth(5.0);
glBegin(GL_LINE_STRIP);
for(u=0;u<1.0;u+=0.01)
{
x=0;y=0;
for(k=0;k<4;k++)
{
blend=c[k]*pow(u,k)*pow(1-u,n-k);
x+=cp[k][0]*blend;
y+=cp[k][1]*blend;
}
glVertex2f(x,y);
}
glEnd();
glFlush();
}

void myinit()
{
glClearColor(1.0,1.0,1.0,1.0);
glColor3f(1.0,0.0,0.0);
glPointSize(5.0);
gluOrtho2D(0.0,600,0.0,600.0);
}

int main(int argc, char ** argv)
{
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
glutInitWindowSize(600,600);
glutCreateWindow(“Bezier Curve”);
glutDisplayFunc(display);
myinit();
glutMainLoop();
return 0;
}

OUTPUT :
( click on image to zoom )




ALTERNATIVE SOLUTION :

#include <bits/stdc++.h>
#include <GL/glut.h>
#include <unistd.h>
using namespace std;
int stp = 10;
double X0, Y0, X1, Y1, X2, Y2, itr = 0, incVal = 0.2;

pair <double, double> findPoint(double _X1, double _Y1, double _X2, double _Y2, int dLen)
{
double m = (_Y2 – _Y1) / (_X2 – _X1);
double c = _Y1 – m * _X1;
double seg = abs(_X2 – _X1) / stp;
double xres = min(_X1, _X2) + seg * dLen;
double yres = m * xres + c;
return { xres, yres };
}

void solve()
{
pair<double, double> pcur, pprev;
vector< pair<double, double> > pts1(11), pts2(11);
for (int i = 0; i <= stp; i++)
    {
pts1[i] = findPoint(X0, Y0, X1, Y1, i);
pts2[i] = findPoint(X1, Y1, X2, Y2, i);
}
for (int i = 0; i <= stp; i++)
{
pcur = findPoint(pts1[i].first, pts1[i].second, pts2[i].first, pts2[i].second, i);
if (i != 0)
{
for (int thick = 0; thick < 200; thick++)
{
if(thick <67)
                    glColor3f(1, 0.5, 0); // orange
else if(thick < 133)
                    glColor3f(1, 1, 1); // white
else
                    glColor3f(0, 1, 0); // green
glBegin(GL_LINES);
glVertex2d(pprev.first, pprev.second – thick);
glVertex2d(pcur.first, pcur.second – thick);
glEnd();
}glFlush();
}pprev = pcur;
}
}

void drawStick()
{
glColor3f(0.8, 0.4, 0.2);
glBegin(GL_POLYGON);
glVertex2i(150, 345);
glVertex2i(160, 345);
glVertex2i(160, 60);
glVertex2i(150, 60);
glEnd();
glFlush();
}

void work()
{
glClearColor(0, 0, 0, 1);
glClear(GL_COLOR_BUFFER_BIT);
drawStick();
X0 = 160, Y0 = 340, X1 = 210 + (itr * 3.0) / 4, Y1 = 390 – (itr * 2), X2 = 260 + (itr * 3.0) / 2, Y2 = 340;
solve();
X0 = 260 + (itr*3.0) / 2, Y0 = 340, X1 = 310 + 3 * (itr*3.0) / 4, Y1 = 290 + (itr * 2), X2 = 360 + (itr * 3), Y2 = 340;
solve();
usleep(20000);
itr += incVal;
if (itr > 15)
incVal = -0.1;
else if (itr < 0)
incVal = 0.1;
glutSwapBuffers();
glutPostRedisplay();
}

int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE);
glutInitWindowPosition(0, 0);
glutInitWindowSize(500, 500);
glutCreateWindow(“Bezier Curve”);
glMatrixMode(GL_PROJECTION);
gluOrtho2D(0, 500, 0, 500);
glMatrixMode(GL_MODELVIEW);
glutDisplayFunc(work);
glutMainLoop();
}

OUTPUT:


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