Catmull Rom spline Curve

Dear All,

I am trying to render the Catmull Rom Spline curve. I generated the points using the Catmull Rom curve equation. But when I render these points, instead of curve, I am getting a straight line.

 #include <math.h>
#include <GL/glut.h>
#include <GL/gl.h>
 
 
struct point
{
	float x;
	float y;
};
 
 
 
 
struct point CatmullRoll(float t, struct point p1, struct point p2, struct point p3, struct point p4)
{
 
	float t2 = t*t;
	float t3 = t*t*t;
	struct point v; // Interpolated point
 
	/* Catmull Rom spline Calculation */
 
	v.x = ((-t3 + 2*t2-t)*(p1.x) + (3*t3-5*t2+2)*(p2.x) + (-3*t3+4*t2+t)* (p3.x) + (t3-t2)*(p4.x))/2;
	v.y = ((-t3 + 2*t2-t)*(p1.y) + (3*t3-5*t2+2)*(p2.y) + (-3*t3+4*t2+t)* (p3.y) + (t3-t2)*(p4.y))/2;
	printf("Values of v.x = %f and v.y = %f\n", v.x,v.y);
 
	return v;	
}
 
void initScene()                                                
{
	glClearColor(0.0,0.0,0.0,0.0);
	glShadeModel(GL_FLAT);
}
 
 
void reshape(int w,int h)
{
	glViewport(0,0,(GLsizei)w,(GLsizei)h);
	glMatrixMode(GL_PROJECTION);
	if(w<=h)
		glOrtho(-50.0,50.0,-50.0*(GLfloat)h/(GLfloat)w,50.0*(GLfloat)h/(GLfloat)w,-50.0,50.0);
	else
		glOrtho(-50.0,5.0,-50.0*(GLfloat)w/(GLfloat)h,50.0*(GLfloat)w/(GLfloat)h,-50.0,50.0);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
 
}
void display(void)
{
	float t;
	struct point v;	//Interpolated point 
	struct point p1,p2,p3,p4;
 
	p1.x  = 5.25;p1.y = 5.25;
	p2.x  = 10.5;p2.y = 10.5;
	p3.x  = 40.33;p3.y = 40.33;
	p4.x  = 50.66;p4.y = 50.66;
 
	glClear(GL_COLOR_BUFFER_BIT);
	glColor3f(1.0f,1.0f,1.0f);
	glPointSize(8);
 
	glBegin(GL_POINTS);
		glVertex2f(p1.x,p1.y);
		glVertex2f(p2.x,p2.y);
		glVertex2f(p3.x,p3.y);
		glVertex2f(p4.x,p4.y);
	glEnd();
 
	for(t=0;t<1;t+=0.02)
	{
		v = CatmullRoll(t,p1,p2,p3,p4);
		glBegin(GL_POINTS);
			glVertex2f(v.x,v.y);
		glEnd();
	}
	glFlush();
 
}
 
 
void main(int argc, char *argv[])
{
	glutInit(&amp;argc, argv);
	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGBA);
	glutInitWindowSize(500,500);
	glutInitWindowPosition(100,100);
	glutCreateWindow("Catmull Roll");
	initScene();
	glutDisplayFunc(display);	
	glutReshapeFunc(reshape);
	glutMainLoop();
}

[ZbuffeR]

p1.x = 5.25;p1.y = 5.25;
p2.x = 10.5;p2.y = 10.5;
p3.x = 40.33;p3.y = 40.33;
p4.x = 50.66;p4.y = 50.66;

Ok, so these points are aligned.

v = CatmullRoll(t,p1,p2,p3,p4);
glBegin(GL_POINTS);
glVertex2f(v.x,v.y);
glEnd();

And now you interpolate between them... so you will still get a straight line, but with a much higher resolution though
Try with more random coords for your control points !

By the way, this is not really OpenGL, may be more at its place on the GL Math & Algo forum ...

also, you might get better results with a bezier curve:

float bezierCurve(float t, float p0, float p1, float p2, float p3)
{
    float t2 = t * t;
    float t3 = t2 * t;
    return p0
        +  3*(p1 - p0) * t
        +  3*(p2 - 2*p1 + p0) * t2
        +  (p3 - 3*(p2 - p1) - p0) * t3;
}