example of simulating moving balls with Box2D and SFML

moving_balls.cpp

#include <SFML/Graphics.hpp>
#include "Box2D/Box2D.h"

static const float SCALE = 30.f;

void create_balls_and_move_them() 
{
	// define the world;
	b2Vec2 gravity(b2Vec2(0.f,9.8f)); // check if it dont work
	b2World world(gravity);

	//create the ground
	// create the ground before creating balls
	create_ground(world);

	// create the window
	sf::RenderWindow window(sf::VideoMode(800,600,32),"Moving Boxes");
	window.setFramerateLimit(60);
	sf::Event event;
	while(window.isOpen())
	{
		while(window.pollEvent(event))
		{
			if (event.type == sf::Event::Closed)
				window.close();
		}

		// create the balls
		if (sf::Mouse::isButtonPressed(sf::Mouse::Right))
		{
			float32 x = (float32)sf::Mouse::getPosition(window).x;
			float32 y = (float32)sf::Mouse::getPosition(window).y;
			create_ball(world,x,y);
		}

		//load ball texture
		sf::Texture ball_texture;
		ball_texture.loadFromFile("ball-hd.png");
		sf::Sprite ball_sprite;
		ball_sprite.setOrigin(16.f,16.f);
		ball_sprite.setTexture(ball_texture);

		//load ground texture
		sf::Texture ground_texture;
		ground_texture.loadFromFile("ground.png");
		sf::Sprite ground_sprite;
		ground_sprite.setTexture(ground_texture);
		ground_sprite.setPosition(1.f,510.f);

		//simulate the world
		world.Step(1/60.f,8,3);

		//clear window
		window.clear(sf::Color::White);

		//iterator over the bodies of the world
		for (b2Body *body_iterator = world.GetBodyList(); body_iterator !=0; body_iterator= body_iterator-> GetNext())
		{
			//world.Step(1/60.f,8,3);
			if (body_iterator-> GetType() == b2_dynamicBody)
			{

				ball_sprite.setPosition(body_iterator-> GetPosition().x*SCALE, body_iterator-> GetPosition().y*SCALE);
				window.draw(ball_sprite);
			}
			else
			{			
				window.draw(ground_sprite);
			}
		}
	
		window.display(); 
	}
}

void create_ball(b2World& world, float32 x, float32 y)
{
	//define the body
	b2BodyDef ball_bodydef;
	ball_bodydef.position.Set(x/SCALE, y/SCALE);
	ball_bodydef.type = b2_dynamicBody;

	//create the body
	b2Body *ball_body = world.CreateBody(&ball_bodydef);

	//define the shape
	b2CircleShape ball_shape;
	ball_shape.m_radius= 50.f/SCALE;

	//define the fixture
	b2FixtureDef ball_fixturedef;
	ball_fixturedef.shape = &ball_shape;
	ball_fixturedef.density = 1.5f;
	ball_fixturedef.friction = 0.3f;
	ball_fixturedef.restitution = 0.5f;

	//attach the fixture with body
	ball_body -> CreateFixture(&ball_fixturedef);

}
void create_ground(b2World& world)
{
	b2BodyDef ground_bodydef;
	ground_bodydef.type = b2_staticBody;
	ground_bodydef.position.Set(1.f/SCALE,533.f/SCALE);
	b2Body *ground_body= world.CreateBody(&ground_bodydef);
	b2PolygonShape ground_shape;
	ground_shape.SetAsBox(800.f/SCALE, 50.f/SCALE);
	b2FixtureDef ground_fixturedef;
	ground_fixturedef.density = 1.f;
	ground_fixturedef.friction	= 0.f;
	ground_fixturedef.shape = &ground_shape;
	ground_body -> CreateFixture(&ground_fixturedef);
}

int main()
{
	create_balls_and_move_them();

	return 0;
}