Box2D tutorial 1 - main program with OpenGL rendering

//http://www.youtube.com/user/thecplusplusguy
//The Box2D main program with OpenGL and SDL
#include <iostream>
#include <SDL/SDL.h>
#include <SDL/SDL_image.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include <Box2D/Box2D.h>

const int WIDTH=640;
const int HEIGHT=480;
const float M2P=20;
const float P2M=1/M2P;
b2World* world;




b2Body* addRect(int x,int y,int w,int h,bool dyn=true)
{
    b2BodyDef bodydef;
    bodydef.position.Set(x*P2M,y*P2M);
    if(dyn)
        bodydef.type=b2_dynamicBody;
    b2Body* body=world->CreateBody(&bodydef);

    b2PolygonShape shape;
    shape.SetAsBox(P2M*w/2,P2M*h/2);

    b2FixtureDef fixturedef;
    fixturedef.shape=&shape;
    fixturedef.density=1.0;
    body->CreateFixture(&fixturedef);

}

void drawSquare(b2Vec2* points,b2Vec2 center,float angle)
{
    glColor3f(1,1,1);
    glPushMatrix();
        glTranslatef(center.x*M2P,center.y*M2P,0);
        glRotatef(angle*180.0/M_PI,0,0,1);
        glBegin(GL_QUADS);
            for(int i=0;i<4;i++)
                glVertex2f(points[i].x*M2P,points[i].y*M2P);
        glEnd();
    glPopMatrix();
}

void init()
{
    glMatrixMode(GL_PROJECTION);
        glOrtho(0,WIDTH,HEIGHT,0,-1,1);
    glMatrixMode(GL_MODELVIEW);
    glClearColor(0,0,0,1);
    world=new b2World(b2Vec2(0.0,9.81));
    addRect(WIDTH/2,HEIGHT-50,WIDTH,30,false);
}

void display()
{
    glClear(GL_COLOR_BUFFER_BIT);
    glLoadIdentity();
    b2Body* tmp=world->GetBodyList();
    b2Vec2 points[4];
    while(tmp)
    {
        for(int i=0;i<4;i++)
            points[i]=((b2PolygonShape*)tmp->GetFixtureList()->GetShape())->GetVertex(i);

        drawSquare(points,tmp->GetWorldCenter(),tmp->GetAngle());
        tmp=tmp->GetNext();
    }
}

int main(int argc,char** argv)
{
    SDL_Init(SDL_INIT_EVERYTHING);
    SDL_SetVideoMode(640,480,32,SDL_OPENGL);
    Uint32 start;
    SDL_Event event;
    bool running=true;
    init();
    while(running)
    {
        start=SDL_GetTicks();
        while(SDL_PollEvent(&event))
        {
            switch(event.type)
            {
                case SDL_QUIT:
                    running=false;
                    break;
                case SDL_KEYDOWN:
                    switch(event.key.keysym.sym)
                    {
                        case SDLK_ESCAPE:
                            running=false;
                            break;
                    }
                    break;
                case SDL_MOUSEBUTTONDOWN:
                    addRect(event.button.x,event.button.y,20,20,true);
                    break;

            }
        }
        display();
        world->Step(1.0/30.0,8,3);  //update
        SDL_GL_SwapBuffers();
        if(1000.0/30>SDL_GetTicks()-start)
            SDL_Delay(1000.0/30-(SDL_GetTicks()-start));
    }
    SDL_Quit();
}