OpenGL particle system - opengl

Question

I'm trying to simulate a particle system using OpenGl but I can't get it to work, this is what I have so far:
#include <GL/glut.h>
int main (int argc, char **argv){
// data allocation, various non opengl stuff
............
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE );
glutInitWindowPosition(100,100);
glutInitWindowSize(size, size);
glPointSize (4);
glutCreateWindow("test gl");
............
// initial state, not opengl
............
glViewport(0,0,size,size);
glutDisplayFunc(display);
glutIdleFunc(compute);
glutMainLoop();
}
void compute (void) {
// change state not opengl
glutPostRedisplay();
}
void display (void) {
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_POINTS);
for(i = 0; i<nparticles; i++) {
// two types of particles
if (TYPE(particle[i]) == 1) glColor3f(1,0,0);
else glColor3f(0,0,1);
glVertex2f(X(particle[i]),Y(particle[i]));
}
glEnd();
glFlush();
glutSwapBuffers();
}
I get a black window after a couple of seconds (the window has just the title bar before that). Where do I go wrong?
LE: the x and y coordinates of each particle are within the interval (0,size)

Answer 1

Try to make these changes in your code:
move the Main function at the end of the file
glPoinSize call belongs to the Display function
then you should provide a function to handle resizing of the window glutReshapeFunc(reshape), something like this
void reshape(int w, int h)
{
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0, (GLdouble) w, 0.0, (GLdouble) h);
}
glFlush is called from glutSwapBuffers function so you don't need it there
insert this code (after glutCreateWindow call) to set the initial position for the projection
glClearColor(0.2, 0.0, 0.0, 0.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, 10, 0.0, 10, -1.0, 1.0);