n-body-sim/simulator.cpp at main · b0bhat/n-body-sim · GitHub

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#include "simulator.h"

std::vector<CollisionPoint> collisionPoints;

bool isSpacePressed() {
    HWND foregroundWindow = GetForegroundWindow();
    DWORD currentProcessId;
    GetWindowThreadProcessId(foregroundWindow, &currentProcessId);
    DWORD thisProcessId = GetCurrentProcessId();
    if (currentProcessId != thisProcessId) {
        return false;
    }
    return GetAsyncKeyState(VK_SPACE) & 0x8000;
}

void restartExecutable(GLFWwindow* window) {
    std::cout << "Restarting...\n";
    run(window);
    return;
}

void hsvToRgb(float h, float s, float v, float &r, float &g, float &b) {
    int i = floor(h * 6);
    float f = h * 6 - i;
    float p = v * (1 - s);
    float q = v * (1 - f * s);
    float t = v * (1 - (1 - f) * s);

    switch (i % 6) {
        case 0: r = v, g = t, b = p; break;
        case 1: r = q, g = v, b = p; break;
        case 2: r = p, g = v, b = t; break;
        case 3: r = p, g = q, b = v; break;
        case 4: r = t, g = p, b = v; break;
        case 5: r = v, g = p, b = q; break;
    }
}

void updateBodies(std::vector<Body>& particles, std::vector<Body*>& mobileParticles, double dt) {
    const size_t maxOrbitSize = 1000;
    const float squaredLimit = 1.5 * 1.5;
    const double collisionThreshold = 0.000001;

    #pragma omp parallel for
    for (size_t i = 0; i < mobileParticles.size(); ++i) {
        Body* particle = mobileParticles[i];
        if (!particle->alive)
            continue;

        float fx = 0.0, fy = 0.0;
        std::vector<CollisionPoint> localCollisionPoints;

        for (size_t j = 0; j < particles.size(); ++j) {
            Body* other = &particles[j];
            if (particle == other || !other->alive)
                continue;

            float dx = particle->x - other->x;
            float dy = particle->y - other->y;
            double distanceSquared = dx * dx + dy * dy;

            if (particle->collision && other->mobile && distanceSquared < collisionThreshold) {
                float totalMass = particle->mass + other->mass;
                float invTotalMass = 1.0 / totalMass;
                #pragma omp critical
                {
                    particle->vx = (particle->mass * particle->vx + other->mass * other->vx) * invTotalMass;
                    particle->vy = (particle->mass * particle->vy + other->mass * other->vy) * invTotalMass;
                    particle->mass = totalMass;
                    other->alive = false;

                    localCollisionPoints.emplace_back(CollisionPoint{particle->x, particle->y, totalMass, std::chrono::steady_clock::now()});
                }
                continue;
            }

            if (other->massive) {
                float distance = std::max(distanceSquared, 0.1);
                if (distance <= 1.0) {
                    float force = (G * particle->mass * other->mass) / (distance);
                    fx += force * (-dx / distance);
                    fy += force * (-dy / distance);
                }
            }
        }

        float dtByMass = dt / particle->mass;
        float ax = fx * dtByMass;
        float ay = fy * dtByMass;

        #pragma omp atomic
        particle->vx += ax;
        #pragma omp atomic
        particle->vy += ay;
        #pragma omp atomic
        particle->x += particle->vx * dt;
        #pragma omp atomic
        particle->y += particle->vy * dt;

        particle->orbit.push_back({particle->x, particle->y}); // expensive operation
        while (particle->orbit.size() > maxOrbitSize) {
            particle->orbit.erase(particle->orbit.begin());
        }
        if ((particle->x * particle->x + particle->y * particle->y) > squaredLimit) {
            particle->alive = false;
        }
        #pragma omp critical
        {
            collisionPoints.insert(collisionPoints.end(), localCollisionPoints.begin(), localCollisionPoints.end());
        }
    }
}

void drawCollisionDots() {
    auto currentTime = std::chrono::steady_clock::now();
    for (auto it = collisionPoints.begin(); it != collisionPoints.end();) {
        auto elapsedTime = std::chrono::duration_cast<std::chrono::milliseconds>(currentTime - it->timestamp).count();
        if (elapsedTime >= 500) {
            it = collisionPoints.erase(it);
        } else {
            float alpha = std::exp(-elapsedTime / 200.0f);
            glPointSize(std::log(it->mass) * alpha);
            glBegin(GL_POINTS);
            glColor4f(1.0f, 1.0f, 1.0f, alpha);
            glVertex2f(it->x, it->y);
            ++it;
            glEnd();
        }
    }
}

void drawOrbit(const Body& particle, float trailAlpha) {
    glBegin(GL_LINE_STRIP);
    for (size_t i = 0; i < particle.orbit.size(); ++i) {
        float alpha = particle.currentAlpha - std::pow(trailAlpha, static_cast<float>(i) / particle.orbit.size());
        //std::cout << alpha << std::endl;
        glColor4f(particle.color.r, particle.color.g, particle.color.b, alpha);
        glVertex2d(particle.orbit[i].first, particle.orbit[i].second);
    }
    glEnd();
    if (particle.alive) {
        float trailLength = std::sqrt(particle.vx * particle.vx + particle.vy * particle.vy);
        glBegin(GL_LINE_STRIP);
        size_t startIndex = particle.orbit.size() > trailLength ? particle.orbit.size() - trailLength : 0;
        for (size_t i = startIndex; i < particle.orbit.size(); ++i) {
            glColor4f(particle.color.r, particle.color.g, particle.color.b, 1.0);
            glVertex2d(particle.orbit[i].first, particle.orbit[i].second);
        }
        glEnd();
    } else {
        particle.currentAlpha = std::max(particle.currentAlpha - 0.01, 0.0);
    }
}

void computePosVel(
    float& x, float& y, float& vx, float& vy,
    float minVel, float maxVel, float minRadius, float maxRadius,
    std::mt19937& gen) {
    std::uniform_real_distribution<float> vel_dist(minVel, maxVel);
    std::uniform_real_distribution<float> radius_dist(minRadius, maxRadius);
    std::uniform_real_distribution<float> angle_dist(0.0, 2.0 * pi);
    float radius = radius_dist(gen);
    float angle = angle_dist(gen);

    x = radius * cos(angle);
    y = radius * sin(angle);
    float tangent_angle = atan2(y, x) + pi / 2;
    std::uniform_real_distribution<float> velocity_angle_dist(tangent_angle - pi / 5, tangent_angle + pi / 5);
    float velocity_angle = velocity_angle_dist(gen);
    float vel_amount = vel_dist(gen);
    std::uniform_int_distribution<int> sign_gen(0, 1);
    int sign = sign_gen(gen) * 2 - 1;
    vx = sign * cos(velocity_angle) * vel_amount;
    vy = sign * sin(velocity_angle) * vel_amount;
}

int run(GLFWwindow* window) {
    std::ifstream inputFile("settings.txt");
    if (!inputFile.is_open()) {
        std::cerr << "Error opening settings file." << std::endl;
        return 1;
    }
    double dt;
    int singleStart, numBodiesGenerator, collidingBodies, numMainBodies;
    double singleStartDelta;
    float trailAlpha;
    float minMass, maxMass, minHueSize, maxHueSize, minVel, maxVel, minRadius, maxRadius;
    inputFile >> dt >> singleStart >> numBodiesGenerator >> collidingBodies >> numMainBodies
        >> singleStartDelta >> trailAlpha >> minMass >> maxMass >> minHueSize >> maxHueSize
        >> minVel >> maxVel >> minRadius >> maxRadius;
    inputFile.close();
    std::cout << "dt: " << dt << std::endl;
    std::cout << "singleStart: " << singleStart << std::endl;
    std::cout << "numBodiesGenerator: " << numBodiesGenerator << std::endl;
    std::cout << "collidingBodies: " << collidingBodies << std::endl;
    std::cout << "numMainBodies: " << numMainBodies << std::endl;
    std::cout << "singleStartDelta: " << singleStartDelta << std::endl;
    std::cout << "trailAlpha: " << trailAlpha << std::endl;
    std::cout << "minMass: " << minMass << std::endl;
    std::cout << "maxMass: " << maxMass << std::endl;
    std::cout << "minHueSize: " << minHueSize << std::endl;
    std::cout << "maxHueSize: " << maxHueSize << std::endl;
    std::cout << "minVel: " << minVel << std::endl;
    std::cout << "maxVel: " << maxVel << std::endl;
    std::cout << "minRadius: " << minRadius << std::endl;
    std::cout << "maxRadius: " << maxRadius << std::endl;

    std::cout << "Press SPACE to restart." << std::endl;

    std::random_device rd;
    std::mt19937 gen(rd());
    std::uniform_real_distribution<double> mass_dist(minMass, maxMass);
    std::uniform_real_distribution<float> hue_size_dist(minHueSize, maxHueSize);

    std::uniform_real_distribution<float> color_dist(0.3, 1.0);
    float x_s, y_s, vx_s, vy_s;
    computePosVel(x_s, y_s, vx_s, vy_s, minVel, maxVel, minRadius, maxRadius, gen);
    std::uniform_real_distribution<float> x_dist(x_s, x_s + singleStartDelta);
    std::uniform_real_distribution<float> y_dist(y_s, y_s + singleStartDelta);

    float colorStart = color_dist(gen);
    float colorEnd = colorStart + hue_size_dist(gen);
    std::uniform_real_distribution<float> hue_range_dist(colorStart, colorEnd);

    std::vector<Body> particles;
    // std::vector<Body*> massiveParticles;
    std::vector<Body*> mobileParticles;

    collisionPoints.clear();

    for (int i = 0; i < numBodiesGenerator; ++i) {

        float x, y, vx, vy;
        computePosVel(x, y, vx, vy, minVel, maxVel, minRadius, maxRadius, gen);
        double mass = mass_dist(gen);
        bool mobile = true;
        bool massive = true;
        bool collision = false;
        if (collidingBodies == 1) {
            collision = true;
        }
        bool alive = true;
        float hue = hue_range_dist(gen);
        float lightness = color_dist(gen);
        float saturation = color_dist(gen);
        if (singleStart == 1) {
            x = x_dist(gen);
            y = y_dist(gen);
            vx = vx_s/2;
            vy = vy_s/2;
            mass = 1e2;
            massive = false;
            float hue = static_cast<float>((x - x_s) / singleStartDelta);
            hue = fmod(hue + 1.0f, 1.0f);
            hue = colorStart + hue * (colorEnd - colorStart);
        }
        float r, g, b;
        hsvToRgb(hue, saturation, lightness, r, g, b);
        Color color = Color(r,g,b);
        particles.emplace_back(x, y, vx, vy, mass, mobile, massive, collision, alive, color);
    }
    if (numMainBodies == 1) {
        particles.emplace_back(0.0, 0.0, 0.0, 0.0, 1e7, false, true, false, true, Color(1.0, 1.0, 1.0));
    } else if (numMainBodies >= 2) {
        particles.emplace_back(-0.1, 0.0, 0.0, 0.0, 1e6, false, true, false, true, Color(1.0, 1.0, 1.0));
        particles.emplace_back(0.1, 0.0, 0.0, 0.0, 1e6, false, true, false, true, Color(1.0, 1.0, 1.0));
    }
    if (numMainBodies == 3) {
        particles.emplace_back(0.0, 0.15, 0.0, 0.0, 1e6, false, true, false, true, Color(1.0, 1.0, 1.0));
    }

    // for (auto& particle : particles) {
    //     if (particle.massive) {
    //         massiveParticles.push_back(&particle);
    //     }
    // }

    for (auto& particle : particles) {
        if (particle.mobile) {
            mobileParticles.push_back(&particle);
        }
    }

    auto start_time = std::chrono::steady_clock::now();
    double lastTime = glfwGetTime();
    int frameCount = 0;
    while (!glfwWindowShouldClose(window)) {
        if (isSpacePressed()) {
            return 0;
        }
        auto current_time = std::chrono::steady_clock::now();
        auto elapsed_time = std::chrono::duration_cast<std::chrono::minutes>(current_time - start_time).count();
        if (elapsed_time >= 3) {
            return 0;
        }
        glClear(GL_COLOR_BUFFER_BIT);
        drawCollisionDots();
        frameCount++;
        for (const auto& particle : particles) {
            drawOrbit(particle, trailAlpha);
            if (particle.alive) {
                glPointSize(std::log(particle.mass)/3);
                glBegin(GL_POINTS);
                glColor3f(particle.color.r, particle.color.g, particle.color.b);
                glVertex2d(particle.x, particle.y);
                glEnd();
            }
        }
        updateBodies(particles, mobileParticles, dt);
        glfwSwapBuffers(window);
        glfwPollEvents();
        double currentTime = glfwGetTime();
        if (currentTime - lastTime >= 1.0) {
            double fps = frameCount / (currentTime - lastTime);
            std::cout << "Frame Rate: " << fps << " fps" << std::endl;
            frameCount = 0;
            lastTime = currentTime;
        }
    }
    glfwTerminate();
    std::cout << "Closing" << std::endl;
    return 1;
}

int main() {
    if (!glfwInit()) {
        std::cerr << "Failed to initialize GLFW" << std::endl;
        return -1;
    }
    GLFWwindow* window;
    window = glfwCreateWindow(500, 500, "N-Body Simulation", NULL, NULL);
    if (!window) {
        glfwTerminate();
        std::cerr << "Failed to create GLFW window" << std::endl;
        return -1;
    }
    glfwMakeContextCurrent(window);
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    while (true) {
        int result = run(window);
        if (result != 0) {
            return 0;
        }
    }

    std::cout << "Closing" << std::endl;
    return 0;
}