Particle attraction by mouse C with OpenGL

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

int MOUSEX;
int MOUSEY;
int PRESSED_LEFT = 0;
int PRESSED_RIGHT = 0;

//numarul de particule
#define N   100

struct particles {
    float x;
    float y;
    float dx;
    float dy;
    float color[3];
    float r;
} *array, *i;

void mouse(int, int, int, int);
void mouseMotion(int, int);
void display();
void timer(int);

int main(int argc, char **argv)
{
    //alocam memorie pentru particule
    array = (struct particles *)malloc(N*sizeof(struct particles));
    if(!array)
        exit(1);

    srand(time(0));
    //dam coordonate, pas de miscare, marime si culori intimplatoare particulelor
    for(i = array; i < array+N; i++)
    {
        i->x = rand() % 500;
        i->y = rand() % 500;

        //de dx si dy va depinde viteza particulelor
        i->dx = rand() % 500 / 100.0 - 2.5; //-2.5 face ca aproximativ jumate din particule sa se miste
        i->dy = rand() % 500 / 100.0 - 2.5; //in directia opusa a celorlalte jumate

        i->color[0] = rand() % 200 / 200.0; //o valoare intr 0.0 si 1.0 rosu
        i->color[1] = rand() % 200 / 200.0; //verde
        i->color[2] = rand() % 300 / 300.0; //albastru

        i->r = rand() % 5 + 1;
    }

    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
    glutInitWindowSize(500, 500);
    glutInitWindowPosition(100, 100);
    glutCreateWindow("Move Particles");

    //glClearColor(0.9, 0.9, 0.9, 0.9);
    glClearColor(0, 0, 0, 0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0.0, 500.0, 500.0, 0.0, 0.0, 1.0);

    glutDisplayFunc(display);
    timer(0);
    glutMouseFunc(mouse);
    glutMotionFunc(mouseMotion);

    glutMainLoop();
}

void mouse(int button, int state, int x, int y)
{
    //preluam coordonatele mouse-ului in variabilele globale
    MOUSEX = x;
    MOUSEY = y;

    //verificam care buton este apasat
    if(button == GLUT_LEFT_BUTTON)
        PRESSED_LEFT = state == GLUT_DOWN;
    else if(button == GLUT_RIGHT_BUTTON)
        PRESSED_RIGHT = state == GLUT_DOWN;
}

//miscind mouse-ul cu un buton apasat se chama aceasta functie
void mouseMotion(int x, int y)
{
    MOUSEX = x;
    MOUSEY = y;
}

void timer(int p)
{
    display();

    for(i = array; i < array+N; i++)
    {
        //nu dam voie particulelor sa iasa din limitele ferestrei
        if(i->x > 495 || i->x < 5)
            i->dx *= -1;
        if(i->y > 495 || i->y < 5)
            i->dy *= -1;

        //punem in miscare particulele
        i->x += i->dx;
        i->y += i->dy;

        //daca e apasat butonul sting, atragem particulele
        if(PRESSED_LEFT)
        {
            float dist = sqrt((i->x - MOUSEX)*(i->x - MOUSEX) + (i->y - MOUSEY)*(i->y - MOUSEY));
            i->x += 6 * (MOUSEX - i->x) / dist; //forta de atragere
            i->y += 6 * (MOUSEY - i->y) / dist;
        }

        //daca e apasat butonul drept, respingem particulele
        else if(PRESSED_RIGHT)
        {
            float dist = sqrt((i->x - MOUSEX)*(i->x - MOUSEX) + (i->y - MOUSEY)*(i->y - MOUSEY));
            i->x -= 7 * (MOUSEX - i->x) / dist; //forta de respingere mai mare ca cea de atragere
            i->y -= 7 * (MOUSEY - i->y) / dist;
        }
    }

    //timer() se va rechema fiecare 10 milisecunde
    glutTimerFunc(10, timer, 0);
}

void display()
{
    glClear(GL_COLOR_BUFFER_BIT);

    //desenam particulele de diferite marimi si culori
    float k;
    for(i = array; i < array+N; i++)
    {
        glColor3f(i->color[0], i->color[1], i->color[2]);
        glBegin(GL_POLYGON);
        for(k = 0; k < 2*M_PI; k+=0.1)
            glVertex2f(i->r*cos(k)+i->x, i->r*sin(k)+i->y);
        glEnd();
    }


    glFlush();
    glutSwapBuffers();
}