قبلا در مورد Box2D مطلب کوتاهی نوشتم در مثال زیر روش drag کردن اجسام را نشان می دهم.
با تغییر در کد خط 89 یعنی مقدار mouse_joint.maxForce مي توان روي قىرت پرتاب اجسام توسط mouse اثر گذاشت.
با تغییر در کد خط 89 یعنی مقدار mouse_joint.maxForce مي توان روي قىرت پرتاب اجسام توسط mouse اثر گذاشت.
package {
import flash.display.Sprite;
import flash.events.Event;
import flash.events.MouseEvent;
import Box2D.Dynamics.*;
import Box2D.Collision.*;
import Box2D.Collision.Shapes.*;
import Box2D.Common.Math.*;
import Box2D.Dynamics.Joints.*;
public class cratetest extends Sprite {
public var m_world:b2World;
public var m_iterations:int = 10;
public var m_timeStep:Number = 1/30;
public var mousePVec:b2Vec2 = new b2Vec2();
public var real_x_mouse:Number;
public var real_y_mouse:Number;
public var pixels_in_a_meter = 30;
public var worldAABB:b2AABB = new b2AABB();
public var gravity:b2Vec2 = new b2Vec2(0.0, 10.0);
public var mouseJoint:b2MouseJoint;
public function cratetest() {
addEventListener(Event.ENTER_FRAME, Update, false, 0, true);
stage.addEventListener(MouseEvent.MOUSE_DOWN, on_mouse_down);
stage.addEventListener(MouseEvent.MOUSE_UP, on_mouse_up);
worldAABB.lowerBound.Set(-100.0, -100.0);
worldAABB.upperBound.Set(100.0, 100.0);
m_world = new b2World(worldAABB, gravity, true);
var body:b2Body;
var bodyDef:b2BodyDef;
var boxDef:b2PolygonDef;
bodyDef = new b2BodyDef();
bodyDef.position.Set(8.5, 13.5);
boxDef = new b2PolygonDef();
var ground_width = 8.5;
var ground_height = 0.5;
boxDef.SetAsBox(ground_width, ground_height);
boxDef.friction = 0.3;
boxDef.density = 0;
bodyDef.userData = new floor();
bodyDef.userData.width = ground_width * 2 * pixels_in_a_meter;
bodyDef.userData.height = ground_height * 2 * pixels_in_a_meter;
addChild(bodyDef.userData);
body = m_world.CreateBody(bodyDef);
body.CreateShape(boxDef);
body.SetMassFromShapes();
for (var i:int = 1; i <=5; i++) {
bodyDef = new b2BodyDef();
bodyDef.position.x = Math.random() * 15 + 1;
bodyDef.position.y = Math.random();
var crate_width:Number = 1.5;
var crate_height:Number = 1.5;
boxDef = new b2PolygonDef();
boxDef.SetAsBox(crate_width, crate_height);
boxDef.density = 1.0;
boxDef.friction = 0.5;
boxDef.restitution = 0.2;
bodyDef.userData = new crate();
bodyDef.userData.width = crate_width * 2 * pixels_in_a_meter;
bodyDef.userData.height = crate_height * 2* pixels_in_a_meter;
body = m_world.CreateBody(bodyDef);
body.CreateShape(boxDef);
body.SetMassFromShapes();
addChild(bodyDef.userData);
}
}
public function Update(e:Event):void {
m_world.Step(m_timeStep, m_iterations);
if (mouseJoint) {
var mouseXWorldPhys = mouseX/pixels_in_a_meter;
var mouseYWorldPhys = mouseY/pixels_in_a_meter;
var p2:b2Vec2 = new b2Vec2(mouseXWorldPhys, mouseYWorldPhys);
mouseJoint.SetTarget(p2);
}
for (var bb:b2Body = m_world.m_bodyList; bb; bb = bb.m_next) {
if (bb.m_userData is Sprite) {
bb.m_userData.x = bb.GetPosition().x * pixels_in_a_meter;
bb.m_userData.y = bb.GetPosition().y * pixels_in_a_meter;
bb.m_userData.rotation = bb.GetAngle() * (180/Math.PI);
}
}
}
public function on_mouse_down(evt:MouseEvent):void {
var body:b2Body = GetBodyAtMouse();
if (body) {
var mouse_joint:b2MouseJointDef = new b2MouseJointDef;
mouse_joint.body1 = m_world.GetGroundBody();
mouse_joint.body2 = body;
mouse_joint.target.Set(mouseX/pixels_in_a_meter, mouseY/pixels_in_a_meter);
mouse_joint.maxForce = 10000;
mouse_joint.timeStep = m_timeStep;
mouseJoint = m_world.CreateJoint(mouse_joint) as b2MouseJoint;
}
}
public function on_mouse_up(evt:MouseEvent):void {
if (mouseJoint) {
m_world.DestroyJoint(mouseJoint);
mouseJoint = null;
}
}
public function GetBodyAtMouse(includeStatic:Boolean=false):b2Body {
real_x_mouse = (stage.mouseX)/pixels_in_a_meter;
real_y_mouse = (stage.mouseY)/pixels_in_a_meter;
mousePVec.Set(real_x_mouse, real_y_mouse);
var aabb:b2AABB = new b2AABB();
aabb.lowerBound.Set(real_x_mouse - 0.001, real_y_mouse - 0.001);
aabb.upperBound.Set(real_x_mouse + 0.001, real_y_mouse + 0.001);
var k_maxCount:int = 10;
var shapes:Array = new Array();
var count:int = m_world.Query(aabb, shapes, k_maxCount);
var body:b2Body = null;
for (var i:int = 0; i < count; ++i) {
if (shapes[i].m_body.IsStatic() == false || includeStatic) {
var tShape:b2Shape = shapes[i] as b2Shape;
var inside:Boolean = tShape.TestPoint(tShape.m_body.GetXForm(), mousePVec);
if (inside) {
body = tShape.m_body;
break;
}
}
}
return body;
}
}
}
