OpenGL array of points animation - arrays

Question

I am trying to animate random point that i have created so they move across the screen and re-appear this is what i have done so far but does not work.the code is not the completed version of what i have i have only posted what i thought would be enough for this question could anyone help me animated the points
void TimerFunc(int value)
{
xpos[0]=xpos[0]+0.25;
glutPostRedisplay();
glutTimerFunc(25, TimerFunc, 1);
}
struct Point
{
float rship;
};
std::vector< Point > points;
void display(void)
{
glClear (GL_COLOR_BUFFER_BIT); /* clear window */
glColor3f(1.0, 1.0, 1.0); /* white drawing objects */
/* define object to be drawn as a square polygon */
//Draw points
glEnableClientState( GL_VERTEX_ARRAY );
glVertexPointer( 2, GL_FLOAT, sizeof(Point), &points[0].x );
glPointSize( 1 ); //1 pixel dot
glDrawArrays( GL_POINTS, 0, points.size() );
glDisableClientState( GL_VERTEX_ARRAY );
//glEnable( GL_POINT_SMOOTH );/*round smooth points*/
glFlush(); /* execute drawing commands in buffer */
}
int main(int argc, char** argv)
for( int i = 0; i <250; ++i )
{
Point pt;
pt.x = -100 + (rand() % 200);
pt.y = -100 + (rand() % 200);
points.push_back(pt);
xpos[i] = pt.x;
ypos[i] = pt.y;
}

Answer 1

Quick 'n dirty:
#include <GL/glut.h>
#include <vector>
#include <cstdlib>
struct Point
{
float x, y;
unsigned char r, g, b, a;
};
std::vector< Point > points;
void timer( int value )
{
// move all points left each frame
for( size_t i = 0; i < points.size(); ++i )
{
points[i].x -= 1;
// wrap point around if it's moved off
// the edge of our 100x100 area
if( points[i].x < -50 )
{
points[i].x = 100 + points[i].x;
}
}
glutPostRedisplay();
glutTimerFunc(30, timer, 1);
}
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-50, 50, -50, 50, -1, 1);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
// draw
glColor3ub( 255, 255, 255 );
glEnableClientState( GL_VERTEX_ARRAY );
glEnableClientState( GL_COLOR_ARRAY );
glVertexPointer( 2, GL_FLOAT, sizeof(Point), &points[0].x );
glColorPointer( 4, GL_UNSIGNED_BYTE, sizeof(Point), &points[0].r );
glPointSize( 3.0 );
glDrawArrays( GL_POINTS, 0, points.size() );
glDisableClientState( GL_VERTEX_ARRAY );
glDisableClientState( GL_COLOR_ARRAY );
glFlush();
glutSwapBuffers();
}
void reshape(int w, int h)
{
glViewport(0, 0, w, h);
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE);
glutInitWindowSize(640,480);
glutCreateWindow("Scrolling Points");
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutTimerFunc(30, timer, 1);
// populate points
for( size_t i = 0; i < 1000; ++i )
{
Point pt;
pt.x = -50 + (rand() % 100);
pt.y = -50 + (rand() % 100);
pt.r = rand() % 255;
pt.g = rand() % 255;
pt.b = rand() % 255;
pt.a = 255;
points.push_back(pt);
}
glutMainLoop();
return 0;
}