Question

我正在使用box2d。我有一个或多个椭圆在屏幕上弹跳，我希望在椭圆之间产生一个关节，当它们彼此相距一定距离时。我想问题是如何确定Box2d世界中一个身体的坐标位置

到目前为止，我有：

import shiffman.box2d.*;
import org.jbox2d.collision.shapes.*;
import org.jbox2d.common.*;
import org.jbox2d.dynamics.joints.*;
import org.jbox2d.collision.shapes.Shape;
import org.jbox2d.dynamics.*;
import org.jbox2d.common.*;
import org.jbox2d.dynamics.*;
import org.jbox2d.dynamics.contacts.*;

// A reference to our box2d world
Box2DProcessing box2d;

Mover[] movers = new Mover[99];

void setup() {
  size(1640,1360);
  smooth();

  box2d = new Box2DProcessing(this);
  box2d.createWorld();
  // No global gravity force
  box2d.setGravity(0,0);
  for (int i = 0; i < movers.length; i++) {
    movers[i] = new Mover(random(8,16),random(width),random(height),random(-100,100));
  }
}

void draw() {
  background(255);

  box2d.step();

  for (int i = 0; i < movers.length; i++) {
    for (int s = 0; s < movers.length; s++) {
    Vec2 force = movers[s].attract(movers[i]);
    movers[i].applyForce(force);

*******************This is the part I can't figure out*****************
    ////if(distance between mover[i] and mover[s]<10){create a join as follows:
    //DistanceJointDef djd = new DistanceJointDef();
    //// Connection between previous particle and this one
    //djd.bodyA = mover[s].body;
    //djd.bodyB = mover[i].body;
    //// Equilibrium length
    //djd.length = box2d.scalarPixelsToWorld(len);
    //// Make the joint. 
    //DistanceJoint dj = (DistanceJoint) box2d.world.createJoint(djd);
    //}
************************************************************************        
    }
     movers[i].display(); 
  }
}



class Mover {

  Body body;
  float r;
  float G;


  Mover(float r_, float x, float y,float G_) {  
    r = r_;
    G=G_;
    // Define a body
    BodyDef bd = new BodyDef();
    bd.type = BodyType.DYNAMIC;

    // Set its position
    bd.position = box2d.coordPixelsToWorld(x,y);
    body = box2d.world.createBody(bd);

    // Make the body's shape a circle
    CircleShape cs = new CircleShape();
    cs.m_radius = box2d.scalarPixelsToWorld(r);

    // Define a fixture
    FixtureDef fd = new FixtureDef();
    fd.shape = cs;
    // Parameters that affect physics
    fd.density = 100;
    fd.friction = 10.3;
    fd.restitution = 0.005;

    body.createFixture(fd);

    body.setLinearVelocity(new Vec2(0,0));
    body.setAngularVelocity(0);
  //Strength of force
  }

    Vec2 attract(Mover m) {
    Vec2 pos = body.getWorldCenter();    
    Vec2 moverPos = m.body.getWorldCenter();
    // Vector pointing from mover to attractor
    Vec2 force = pos.sub(moverPos);
    float distance = force.length();
    // Keep force within bounds
    distance = constrain(distance,10,50);
    force.normalize();
    float strength = ((G * 10 * m.body.m_mass) / (distance * distance)/2); // Calculate gravitional force magnitude
    force.mulLocal(strength);         // Get force vector --> magnitude * direction
    return force;
  }

  void applyForce(Vec2 v) {
    body.applyForce(v, body.getWorldCenter());
  }


  void display() {
    // We look at each body and get its screen position
    Vec2 pos = box2d.getBodyPixelCoord(body);
    // Get its angle of rotation
    float a = body.getAngle();
    pushMatrix();
    translate(pos.x,pos.y);
    rotate(a);
    fill(150);
    stroke(0);
    strokeWeight(1);
    ellipse(0,0,r*2,r*2);
    line(0,0,r,0);
    popMatrix();
  }
}

Answer 1

供公众参考，最后我做了

 Vec2 pos_s = box2d.getBodyPixelCoord(movers[s].body);
   float res=dist(pos_s.x,pos_s.y,pos_i.x,pos_i.y);
     //print(";"+res+";");

   if ( res<100&res>-100 ) {
}

如何确定处理

1 个答案: