[Box2D]为什么我的b2Body卡在0; 0？

Question

作为我的项目的第一步，我想用2D物理学来创造一个世界。由于我对OpenGL有一定的了解，因此我尝试在项目中一起使用这两个。

在变得复杂之前，我只是想让一个方盒掉在地上。

问题是： 我有3个文件（main.cpp physique.cpp和affichage.cpp）和2个标头（physique.h affichage.h）。为了能够在不同文件中操纵我的身体，我制作了一个全局变量，该变量是指向我的身体的指针（该指针称为body）。 我在Bigque的physique.cpp中创建自己的世界，身体和地面。我将身体的位置声明为（1; 4）。但是每次我叫cout<<body->GetPosition().x<<endl时，我在第1帧得到0 ...

这是physique.cpp

#include "physique.h"

extern int com;
extern unsigned int fps;

float bodyWidth=0.5f;
float bodyHeight=0.5f;
float groundWidth=10.0f;
float groundHeight=0.5f;

b2Body* body;
b2Body* groundBody;
b2World* ptrWorld;
void BigBang(){
  //DEFINITION WORLD
  b2Vec2 gravity(0.0f, 0.0f);
  b2World world(gravity);
  ptrWorld = &world;

  //DEFINITION GROUND
  b2BodyDef groundBodyDef;
  groundBodyDef.type = b2_staticBody;
  groundBodyDef.position.Set(0.0f,-groundHeight);
  groundBody = world.CreateBody(&groundBodyDef); //renvoie un pointeur
  b2PolygonShape groundBox;
  groundBox.SetAsBox(groundWidth, groundHeight); //2*groundWith units wide and 2*groundHeight units tall;
  groundBody->CreateFixture(&groundBox, 0.0f);

  //DEFINITION CUBE
  b2BodyDef bodyDef;
  bodyDef.type = b2_dynamicBody;
  bodyDef.position.Set(1.0f, 4.0f);
  bodyDef.angle = 0;
  body = world.CreateBody(&bodyDef); //renvoie un pointeur
  b2PolygonShape dynamicBox;
  dynamicBox.SetAsBox(bodyWidth, bodyHeight);
  b2FixtureDef fixtureDef;
  fixtureDef.shape = &dynamicBox;
  fixtureDef.density = 0.0f;
  fixtureDef.friction = 0.3f;
  body->CreateFixture(&fixtureDef);
}
void PhysicEngine(){
  float32 timeStep = fps;
  int32 velocityIterations = 6;
  int32 positionIterations = 2;
  ptrWorld->Step(timeStep, velocityIterations, positionIterations);
}

affichage.cpp：

//INCLUDES
#include "affichage.h"

//VARIABLES
GLfloat deplacement;

extern int previousTime;
extern int currentTime;
extern int elapsedTime;
extern unsigned int fps;
extern int com;

extern float groundHeight;
extern float groundWidth;
extern float bodyWidth;
extern float bodyHeight;
extern b2Body* body;
extern b2Body* groundBody;
extern b2World* ptrWorld;


int nTotFrames=0;
GLvoid affichage(){
    glClear(GL_COLOR_BUFFER_BIT);   // Effacement du frame buffer
    glBegin(GL_QUADS); //sol
    glColor3f(1.0f, 0.5f, 0.5f);
    glVertex2f(groundBody->GetLocalCenter().x-groundWidth, groundBody->GetLocalCenter().y+groundHeight);
    glColor3f(1.0f, 0.5f, 0.5f);
    glVertex2f(groundBody->GetLocalCenter().x-groundWidth, groundBody->GetLocalCenter().y-groundHeight);
    glColor3f(1.0f, 0.5f, 0.5f);
    glVertex2f(groundBody->GetLocalCenter().x+groundWidth, groundBody->GetLocalCenter().y-groundHeight);
    glColor3f(1.0f, 0.5f, 0.5f);
    glVertex2f(groundBody->GetLocalCenter().x+groundWidth, groundBody->GetLocalCenter().y+groundHeight);
    glEnd();
    glFlush();

    glBegin(GL_QUADS); //BOX
    glColor3f(0.5f, 0.5f, 0.5f);
    glVertex2f(body->GetLocalCenter().x-bodyWidth, body->GetLocalCenter().y+bodyHeight);
    glColor3f(0.5f, 0.5f, 0.5f);
    glVertex2f(body->GetLocalCenter().x-bodyWidth, body->GetLocalCenter().y-bodyHeight);
    glColor3f(0.5f, 0.5f, 0.5f);
    glVertex2f(body->GetLocalCenter().x+bodyWidth, body->GetLocalCenter().y-bodyHeight);
    glColor3f(0.5f, 0.5f, 0.5f);
    glVertex2f(body->GetLocalCenter().x+bodyWidth, body->GetLocalCenter().y+bodyHeight);
    glEnd();
    glFlush();

    glLoadIdentity();
    gluOrtho2D(-2.0, 4.0, -1.0, 3.0);
    glutSwapBuffers();
}
GLvoid update(int fps){
    glutTimerFunc(fps, update, 100/6); // setups the timer to be called again
    PhysicEngine();
    previousTime = currentTime; // Get the time when the previous frame was rendered
    currentTime = glutGet(GLUT_ELAPSED_TIME);   // Get the current time (in milliseconds) and calculate the elapsed time
    elapsedTime = currentTime - previousTime;
    deplacement = 0.01*elapsedTime;
    glutPostRedisplay();
    nTotFrames++;
}
GLvoid clavier(unsigned char touche, int x, int y) {
    // ESCAPE ou 'q' : fermera l'application
    switch(touche) {
        case 'i':
        break;
        case 'q' : // quitter
        case 27 :
        cout<<nTotFrames;
        exit(0);
        break;
    }
    // Demande a GLUT de reafficher la scene
    glutPostRedisplay();
}

GLvoid clavierUp(unsigned char key, int x, int y){}

这是main.cpp

//MAINFILE
#ifdef __APPLE__ //OpenGL
#include <OpenGL/gl.h>
#include <GLUT/GLUT.h>
#else
#include <GL/gl.h>
#include <GL/glut.h>
#endif

#include <iostream>
#include <math.h>
#include "affichage.h"
#include "physique.h"
using namespace std;

int previousTime;
int currentTime;
int elapsedTime;

extern b2Body* body;

unsigned int fps = 60;

int com=0;  //correspond au numéro de la jambe qui se lève

int main (int argc, char *argv[]){

    float w = 1000;
    float h = 600;

    glutInit(&argc, argv); // Initialisation de GLUT
    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);    // Choix du mode d'affichage (ici RVB)
    glutInitWindowPosition(0,0); // Position initiale de la fenetre GLUT
    glutInitWindowSize(w,h); // Taille initiale de la fenetre GLUT
    glutCreateWindow("DaddyLongLeg - Algo Genetique"); // Creation de la fenetre GLUT
    glClearColor(0.1f, 0.1f, 0.1f, 0.0f);   // Définition de la couleur d'effacement du framebuffer //le fond est noir

    // Définition des fonctions de callbacks
    glutDisplayFunc(affichage);
    glutKeyboardFunc(clavier);
    glutKeyboardUpFunc(clavierUp);
    glutReshapeFunc(reshape);
    glutTimerFunc(1000/fps, update, 0);
    currentTime = glutGet(GLUT_ELAPSED_TIME);
    BigBang();
    glutMainLoop(); // Lancement de la boucle infinie GLUT
    return 0;
}