C++ : How do I make this particle simulation faster? - c++

Question

I have a simple 2D simulation which has particles travelling at given velocities and could collide with each other and the walls. But the fps drops when there are more than 500 particles. I want to simulate at least 5000 particles smoothly because I'll be adding more features to the program. Is there a different and efficient approach to this? Thanks!
gas.cpp:
#include<cstdlib>
#include<vector>
#include<glut.h>
#include "gas.h"
#include<time.h>
float t = 1; //time step
void gas::p(float pos_x, float pos_y, float vx, float vy, float mass)
{
srand(time(0));
m = mass;
x = pos_x;
y = pos_y;
velx = vx;
vely = vy;
size = 3;
}
void gas::draw()
{
glColor3f(1, 1, 1);
glVertex2f(x, y);
}
void gas::move(float t)
{
x += velx * t;
y += vely * t;
}
float temp;
//Function to be ran at every frame:
void run(std::vector <gas>& bn)
{
int it = 0;
for (gas& i : bn)
{
int jt = 0;
for (gas& j : bn)
{
if (it != jt)
{
//Handling collisions:
if (abs(i.y - (j.y + j.size)) < 1 && (abs(j.x - i.x) <= i.size + 1) && i.vely < 0)
{
temp = i.vely;
i.vely = j.vely;
j.vely = temp;
}
if (abs(j.y - (i.y + i.size)) < 1 && (abs(i.x - j.x) <= j.size + 1) && i.vely > 0)
{
temp = i.vely;
i.vely = j.vely;
j.vely = temp;
}
if (abs(j.x - (i.x + i.size)) < 1 && (abs(i.y - j.y) <= i.size + 1) && i.velx > 0)
{
temp = i.velx;
i.velx = j.velx;
j.velx = temp;
}
if (abs(i.x - (j.x + j.size)) < 1 && (abs(j.y - i.y) <= i.size + 1) && i.velx < 0)
{
temp = i.velx;
i.velx = j.velx;
j.velx = temp;
}
}
jt += 1;
}
//Boundary Collisions:
if (i.x > 600 - i.size) { i.x = 600 - i.size; i.velx = -i.velx; }
if (i.x < i.size) { i.x = i.size; i.velx = -i.velx; }
if (i.y > 600 - i.size) { i.y = 600 - i.size; i.vely = -i.vely; }
if (i.y < i.size) { i.y = i.size; i.vely = -i.vely; }
i.move(t);
it += 1;
}
}
gas.h:
#pragma once
class gas
{
public:
float m = 1;
float x = 0;
float y = 0;
float velx = 0;
float vely = 0;
float size = 3;
float density = 100;
float r = 1; float g = 1; float b = 1;
void p(float pos_x, float pos_y, float vx, float vy, float mass);
void draw();
void move(float t);
};
void run(std::vector<gas>& bn);
simulate.cpp (main file):
#include<cstdlib>
#include<glut.h>
#include<vector>
#include "gas.h"
#include<thread>
#include<time.h>
void display();
void reshape(int, int);
const int n = 600; //Number of particles
void init()
{
glClearColor(0, 0, 0, 1);
}
std::vector <gas> b(n);
void timer(int)
{
run(b);
glutPostRedisplay();
glutTimerFunc(1000 / 60, timer, 0);
}
void show(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
glutInitWindowPosition(300, 60);
glutInitWindowSize(600, 600);
glutCreateWindow("Particles");
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutTimerFunc(1000, timer, 0); // Args: Time delay per frame in milliseconds, function to be called
init();
glutMainLoop();
}
int main(int argc, char** argv)
{
int it = 0;
for (gas& i : b)
{
srand(it);
i.p(rand() % 600, rand() % 600, (rand() % 10) * pow(-1, it + 1), (rand() % 10) * pow(-1, it), 1);
it += 1;
}
show(argc, argv);
}
void display()
{
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity();
glPointSize(3);
glBegin(GL_POINTS);
for (gas& i : b)
{
i.draw();
}
glEnd();
glutSwapBuffers();
}
void reshape(int w, int h)
{
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, 600, 0, 600);
glMatrixMode(GL_MODELVIEW);
}