CobaltXII/n_body_image.cpp

## n_body_image.cpp
// Emptyness? Awesome.

#define STB_IMAGE_WRITE_IMPLEMENTATION

#include "stb_image_write.h"

#include <vector>
#include <utility>
#include <sstream>
#include <iostream>

typedef float real;

struct body
{
	real x;
	real y;

	real vx;
	real vy;

	body(real _x, real _y)
	{
		x = _x;
		y = _y;

		vx = 0.0f;
		vy = 0.0f;
	}
};

void body_force(std::vector<body>& bodies, real timestep)
{
	const real softening = 10.0f;

	#pragma omp parallel for schedule(dynamic)

	for (int i = 0; i < bodies.size(); i++)
	{
		real fx = 0.0f;
		real fy = 0.0f;

		for (int j = 0; j < bodies.size(); j++)
		{
			if (i == j)
			{
				continue;
			}

			real dx = bodies[j].x - bodies[i].x;
			real dy = bodies[j].y - bodies[i].y;

			real dist_sqr = dx * dx + dy * dy + softening;

			real inv_dist = 1.0f / sqrtf(dist_sqr);

			real inv_dist_3 =
			(
				inv_dist *
				inv_dist *
				inv_dist
			);

			fx += dx * inv_dist_3;
			fy += dy * inv_dist_3;
		}

		bodies[i].vx += timestep * fx;
		bodies[i].vy += timestep * fy;
	}
}

// Entry point for the software renderer.

int main(int argc, char** argv)
{
	std::vector<body> bodies;

	int x_res = 700;
	int y_res = 700;

	unsigned char* img_data = (unsigned char*)malloc(x_res * y_res * 3 * sizeof(unsigned char));

	int stride_in_bytes = x_res * 3;

	const real xr = 1000.0f;
	const real yr = 1000.0f;

	for (int i = 0; i < 20000; i++)
	{
		real r1 = float(rand()) / float(RAND_MAX) * 2.0f - 1.0f;
		real r2 = float(rand()) / float(RAND_MAX) * 2.0f - 1.0f;

		real angx = cos(r1 * 2.0f * M_PI);
		real angy = sin(r1 * 2.0f * M_PI);

		bodies.push_back(body(angx * r2 * xr, angy * r2 * yr));
	}

	for (int i = 0; i < 3600; i++)
	{
		memset(img_data, 0, x_res * y_res * 3 * sizeof(unsigned char));

		body_force(bodies, 5.0f);

		for (int i = 0; i < bodies.size(); i++)
		{
			body& bi = bodies[i];

			bi.x += bi.vx;
			bi.y += bi.vy;

			int x = bi.x / 10.0f + x_res / 2;
			int y = bi.y / 10.0f + y_res / 2;

			if (x >= 0 && x < x_res && y >= 0 && y < y_res)
			{
				img_data[y * stride_in_bytes + x * 3 + 0] = 255;
				img_data[y * stride_in_bytes + x * 3 + 1] = 255;
				img_data[y * stride_in_bytes + x * 3 + 2] = 255;
			}
		}

		std::stringstream path_builder;

		path_builder << "./frame_" << i << ".png";

		stbi_write_png(path_builder.str().c_str(), x_res, y_res, 3, img_data, stride_in_bytes);

		std::cout << i << std::endl;
	}

	free(img_data);

	return 0;
}
	// Emptyness? Awesome.

	#define STB_IMAGE_WRITE_IMPLEMENTATION

	#include "stb_image_write.h"

	#include <vector>
	#include <utility>
	#include <sstream>
	#include <iostream>

	typedef float real;

	struct body
	{
	real x;
	real y;

	real vx;
	real vy;

	body(real _x, real _y)
	{
	x = _x;
	y = _y;

	vx = 0.0f;
	vy = 0.0f;
	}
	};

	void body_force(std::vector<body>& bodies, real timestep)
	{
	const real softening = 10.0f;

	#pragma omp parallel for schedule(dynamic)

	for (int i = 0; i < bodies.size(); i++)
	{
	real fx = 0.0f;
	real fy = 0.0f;

	for (int j = 0; j < bodies.size(); j++)
	{
	if (i == j)
	{
	continue;
	}

	real dx = bodies[j].x - bodies[i].x;
	real dy = bodies[j].y - bodies[i].y;

	real dist_sqr = dx * dx + dy * dy + softening;

	real inv_dist = 1.0f / sqrtf(dist_sqr);

	real inv_dist_3 =
	(
	inv_dist *
	inv_dist *
	inv_dist
	);

	fx += dx * inv_dist_3;
	fy += dy * inv_dist_3;
	}

	bodies[i].vx += timestep * fx;
	bodies[i].vy += timestep * fy;
	}
	}

	// Entry point for the software renderer.

	int main(int argc, char** argv)
	{
	std::vector<body> bodies;

	int x_res = 700;
	int y_res = 700;

	unsigned char* img_data = (unsigned char)malloc(x_res y_res * 3 * sizeof(unsigned char));

	int stride_in_bytes = x_res * 3;

	const real xr = 1000.0f;
	const real yr = 1000.0f;

	for (int i = 0; i < 20000; i++)
	{
	real r1 = float(rand()) / float(RAND_MAX) * 2.0f - 1.0f;
	real r2 = float(rand()) / float(RAND_MAX) * 2.0f - 1.0f;

	real angx = cos(r1 * 2.0f * M_PI);
	real angy = sin(r1 * 2.0f * M_PI);

	bodies.push_back(body(angx * r2 * xr, angy * r2 * yr));
	}

	for (int i = 0; i < 3600; i++)
	{
	memset(img_data, 0, x_res * y_res * 3 * sizeof(unsigned char));

	body_force(bodies, 5.0f);

	for (int i = 0; i < bodies.size(); i++)
	{
	body& bi = bodies[i];

	bi.x += bi.vx;
	bi.y += bi.vy;

	int x = bi.x / 10.0f + x_res / 2;
	int y = bi.y / 10.0f + y_res / 2;

	if (x >= 0 && x < x_res && y >= 0 && y < y_res)
	{
	img_data[y * stride_in_bytes + x * 3 + 0] = 255;
	img_data[y * stride_in_bytes + x * 3 + 1] = 255;
	img_data[y * stride_in_bytes + x * 3 + 2] = 255;
	}
	}

	std::stringstream path_builder;

	path_builder << "./frame_" << i << ".png";

	stbi_write_png(path_builder.str().c_str(), x_res, y_res, 3, img_data, stride_in_bytes);

	std::cout << i << std::endl;
	}

	free(img_data);

	return 0;
	}