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Collision.cpp
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Collision.cpp
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#include "screen.h"
#include "vec2.h"
#include <chrono>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <thread>
using namespace std::chrono_literals;
constexpr float G = 3.0f;
struct Body
{
float r;
float m;
vec2 pos;
vec2 vel;
vec2 acc;
Body()
{
m = 1.0f;
r = 0.2f;
pos = 0;
vel = 0;
acc = 0;
}
Body(float m) : m(m)
{
r = 0.2f * std::cbrt(m);
pos = 0;
vel = 0;
acc = 0;
}
Body(float m, float r) : r(r), m(m)
{
pos = 0;
vel = 0;
acc = 0;
}
void setPos(float x, float y)
{
pos.x = x;
pos.y = y;
}
void PulledBy(const Body& other)
{
float dist = std::sqrt((pos - other.pos) * (pos - other.pos));
acc += G * other.m * (other.pos - pos) / dist / dist /
dist; // vector form of the formula for gravity
}
void Update(float dt)
{
vel += dt * acc;
pos += dt * vel;
acc = 0;
}
};
void Plot(const Body& body, Screen& scr) // render the body
{
scr.PlotCircle(body.pos.x, body.pos.y, body.r);
}
float random(float low, float high)
{
return low + static_cast<float>(rand()) / (static_cast<float>(RAND_MAX / (high - low)));
}
int main()
{
srand(static_cast<unsigned>(time(nullptr)));
Screen scr(0, 0, 5);
constexpr std::size_t n = 20000;
constexpr float dt = 1.0f / 25.0f;
// Initializing first galaxy
Body Centre1(2000.0f, 2.5f);
Centre1.pos = {150.0f, 20.0f};
Centre1.vel = {-5.0f, 0.0f};
Body Bodies1[n];
for(auto& body: Bodies1)
{
float maxRadius = 30.0f; // max radius of the galaxy
float theta = random(0.0f, 2 * M_PIf32); // angle the particle makes with the centre
float r = random(1.0f, maxRadius);
r = r * r / maxRadius; // change distribution of particles (optional)
r += 0.2f * Centre1.r;
body.pos = {r * std::cos(theta), r * std::sin(theta)}; // polar to cartezian coordinates
body.pos += Centre1.pos; // move the particle relative to the centre
float v = std::sqrt(G * Centre1.m / r); // calculate velocity based on radius
body.vel = {v * std::sin(theta),
-v *
std::cos(theta)}; // polar to cartezian coordinates, rotated by 90 degrees
float offset = 0.6f;
body.vel +=
{random(-offset, offset), random(-offset, offset)}; // random offset to velocity
body.vel += Centre1.vel;
body.r = 0.2f;
}
/* Initializing second galaxy */
/* Similar to first */
Body Centre2(2000.0f, 2.5f);
Centre2.pos = -Centre1.pos;
Centre2.vel = -Centre1.vel;
Body Bodies2[n];
for(auto& body: Bodies2)
{
float maxRadius = 30.0f;
float theta = random(0.0f, 2 * M_PIf32);
float r = random(1.0f, maxRadius);
r = r * r / maxRadius;
r += 0.2f * Centre2.r;
body.pos = {r * std::cos(theta), r * std::sin(theta)};
body.pos += Centre2.pos;
float v = std::sqrt(G * Centre2.m / r);
body.vel = {v * std::sin(theta), -v * std::cos(theta)};
// uncomment for opposite direction of rotation
// Bodies2[i].vel=-Bodies2[i].vel;
float offset = 0.6f;
body.vel += {random(-offset, offset), random(-offset, offset)};
body.vel += Centre2.vel;
body.r = 0.2f;
}
while(true)
{
scr.Clear();
// centres attract each other
Centre1.PulledBy(Centre2);
Centre2.PulledBy(Centre1);
// particles are attracted to centres
for(std::size_t i = 0; i < n; i++)
{
Bodies1[i].PulledBy(Centre1);
Bodies2[i].PulledBy(Centre1);
Bodies1[i].PulledBy(Centre2);
Bodies2[i].PulledBy(Centre2);
}
// update bodies
Centre1.Update(dt);
Centre2.Update(dt);
for(auto& body: Bodies1)
body.Update(dt);
for(auto& body: Bodies2)
body.Update(dt);
// rendering
Plot(Centre1, scr);
Plot(Centre2, scr);
for(auto&& body: Bodies1)
Plot(body, scr);
for(auto&& body: Bodies2)
Plot(body, scr);
// drawing
if((Centre1.pos - Centre2.pos) * (Centre1.pos - Centre2.pos) < 90.0f * 90.0f)
scr.Zoom(9);
if((Centre1.pos - Centre2.pos) * (Centre1.pos - Centre2.pos) > 110.0f * 110.0f)
scr.Zoom(5);
scr.Draw();
std::this_thread::sleep_for(15ms);
}
return 0;
}