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# I need a C program using OpenGL to create a pendulum that rotates about its string on a mouse click.

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### #1andre_arjun  Members

Posted 19 April 2014 - 05:51 AM

I need it for my mini project. I havent understoods the basics for the rotation yet. I have the source code for creating the pendulum with the thread. I understand that I have to create a matrix for translating the tip of the string to the origin, then rotate the entire figure, and translate it back to the initial position; and multiply all these matrices. I dont understand how to create these matrices, please help me. To create the sphere in the pendulum, I've used recursive defintion of the sphere using tetrahedrons. Please help me, I need the source code. Thank you.
This is the source code so far:
#include<stdio.h>
#include<msclr/glut.h>
#include<math.h>
int n=10;
GLfloat v[4][3]={{0.0,0.0,1.0},{0.0,0.942809,-0.33333},{-0.816497,-0.471405,-0.33333},{0.816497,-0.471405,-0.333333}};
GLfloat a[2][3]={{0.0,0.0,-0.333333},{0.0,10.0,-0.333333}};
void normalize(GLfloat *p)
{
double d=0.0;
int i;
for(i=0;i<3;i++)
d+=p[i]*p[i];
d=sqrt(d);
if(d>0.0)
for(i=0;i<3;i++)
p[i]/=d;
}
void triangle(GLfloat *a,GLfloat *b,GLfloat *c)
{
glBegin(GL_POLYGON);
glNormal3fv(a);
glVertex3fv(a);
glVertex3fv(b);
glEnd();
}
void divide_triangle(GLfloat *a,GLfloat *b,GLfloat *c,int n)
{
GLfloat v1[3],v2[3],v3[3];
int j;
if(n>0)
{
for(j=0;j<3;j++)
v1[j]=a[j]+b[j];
normalize(v1);
for(j=0;j<3;j++)
v2[j]=a[j]+c[j];
normalize(v2);
for(j=0;j<3;j++)
v3[j]=c[j]+b[j];
normalize(v3);
divide_triangle(a,v2,v1,n-1);
divide_triangle(c,v3,v2,n-1);
divide_triangle(b,v1,v3,n-1);
divide_triangle(v1,v2,v3,n-1);
}
else
triangle(a,b,c);
}
void tetrahedron(int n)
{
divide_triangle(v[0],v[1],v[2],n);
divide_triangle(v[3],v[2],v[1],n);
divide_triangle(v[0],v[3],v[1],n);
divide_triangle(v[0],v[2],v[3],n);
}
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glClearColor(1.0,1.0,1.0,1.0);
glColor3f(1.0,0.0,0.0);
tetrahedron(n);
glColor3f(0.0,0.0,1.0);
glBegin(GL_LINES);
glVertex3fv(a[0]);
glVertex3fv(a[1]);
glEnd();
glFlush();
}
void myReshape(int w,int h)
{
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
if(w<=h)
glOrtho(-2.0,2.0,-2.0*(GLfloat)h/(GLfloat)w,2.0*(GLfloat)h/(GLfloat)w,-10.0,10.0);
else
glOrtho(-2.0*(GLfloat)w/(GLfloat)h,2.0*(GLfloat)w/(GLfloat)h,-2.0,2.0,-10.0,10.0);
glMatrixMode(GL_MODELVIEW);
}
void main(int argc,char** argv)
{
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_RGB|GLUT_DEPTH);
glutInitWindowSize(500,500);
glutCreateWindow("Pendulum");
glutReshapeFunc(myReshape);
glutDisplayFunc(display);
glEnable(GL_DEPTH_TEST);
glutMainLoop();
}

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