Rendering joints with Box2D
2009-10-18 00:00:00 来源:WEB开发网In most Box2D projects you can see how to render bodies or attach objects to them, but I couldn’t see any tutorial about rendering joints.
If you look at the classic rendering loop it’s something like this one
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;
bb.m_userData.y = bb.GetPosition().y;
bb.m_userData.rotation = bb.GetAngle() * (180/Math.PI);
}
}
but as you can see, it only renders bodies.
The following script is the same you can find at Simulating a hook with Box2D but I will render the joints with lines.
package {
import flash.display.Sprite;
import flash.events.Event;
import Box2D.Dynamics.*;
import Box2D.Collision.*;
import Box2D.Collision.Shapes.*;
import Box2D.Common.Math.*;
import Box2D.Dynamics.Joints.*;
import flash.events.MouseEvent;
public class distance_joint extends Sprite {
var mouseJoint:b2MouseJoint;
var mousePVec:b2Vec2 = new b2Vec2();
var bd:b2BodyDef;
var the_circle:b2CircleDef = new b2CircleDef();
var circle:b2Body;
var the_box:b2PolygonDef = new b2PolygonDef();
var the_joint:b2DistanceJointDef = new b2DistanceJointDef();
var joint:b2DistanceJoint;
//
public var m_world:b2World;
public var m_iterations:int=10;
public var m_timeStep:Number=1.0/30.0;
//
var my_canvas:Sprite = new Sprite();
public function distance_joint() {
addChild(my_canvas);
// world setup
var worldAABB:b2AABB = new b2AABB();
worldAABB.lowerBound.Set(-100.0, -100.0);
worldAABB.upperBound.Set(100.0, 100.0);
var gravity:b2Vec2=new b2Vec2(0.0,10.0);
var doSleep:Boolean=true;
m_world=new b2World(worldAABB,gravity,doSleep);
// debug draw
var m_sprite:Sprite;
m_sprite = new Sprite();
addChild(m_sprite);
var dbgDraw:b2DebugDraw = new b2DebugDraw();
var dbgSprite:Sprite = new Sprite();
m_sprite.addChild(dbgSprite);
dbgDraw.m_sprite=m_sprite;
dbgDraw.m_drawScale=30;
dbgDraw.m_alpha=1;
dbgDraw.m_fillAlpha=0.5;
dbgDraw.m_lineThickness=1;
dbgDraw.m_drawFlags=b2DebugDraw.e_shapeBit|b2DebugDraw.e_jointBit;
m_world.SetDebugDraw(dbgDraw);
// ground
the_box.SetAsBox(9,0.5);
the_box.density=0;
the_box.friction=0.4;
the_box.restitution=0.1;
bd = new b2BodyDef();
bd.position.Set(8.5, 13);
var ground:b2Body=m_world.CreateBody(bd);
ground.CreateShape(the_box);
ground.SetMassFromShapes();
// roof
the_box.SetAsBox(9,0.5);
the_box.density=0;
the_box.friction=0.4;
the_box.restitution=0.1;
bd = new b2BodyDef();
bd.position.Set(8.5, 0);
var roof:b2Body=m_world.CreateBody(bd);
roof.CreateShape(the_box);
roof.SetMassFromShapes();
// circle
the_circle.radius=2;
the_circle.density=1.0;
the_circle.friction=0.4;
the_circle.restitution=0.3;
bd = new b2BodyDef();
bd.position.Set(6, 2);
circle=m_world.CreateBody(bd);
circle.CreateShape(the_circle);
circle.SetMassFromShapes();
// square
the_box.SetAsBox(1.5,1.5);
the_box.density=1.0;
the_box.friction=0.4;
the_box.restitution=0.1;
bd = new b2BodyDef();
bd.position.Set(2, 2);
var box:b2Body=m_world.CreateBody(bd);
box.CreateShape(the_box);
box.SetMassFromShapes();
// listeners
stage.addEventListener(MouseEvent.MOUSE_DOWN, createMouse);
stage.addEventListener(MouseEvent.MOUSE_UP, destroyMouse);
addEventListener(Event.ENTER_FRAME, Update, false, 0, true);
}
public function createMouse(evt:MouseEvent):void {
var body:b2Body=GetBodyAtMouse(true);
if (body) {
the_joint.Initialize(circle, body, circle.GetWorldCenter(),new b2Vec2(mouseX/30,mouseY/30));
the_joint.collideConnected=true;
joint=m_world.CreateJoint(the_joint) as b2DistanceJoint;
}
}
public function destroyMouse(evt:MouseEvent):void {
if (joint) {
m_world.DestroyJoint(joint);
joint=null;
}
}
public function GetBodyAtMouse(includeStatic:Boolean=false):b2Body {
var mouseXWorldPhys = (mouseX)/30;
var mouseYWorldPhys = (mouseY)/30;
mousePVec.Set(mouseXWorldPhys, mouseYWorldPhys);
var aabb:b2AABB = new b2AABB();
aabb.lowerBound.Set(mouseXWorldPhys - 0.001, mouseYWorldPhys - 0.001);
aabb.upperBound.Set(mouseXWorldPhys + 0.001, mouseYWorldPhys + 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].GetBody().IsStatic()) {
var tShape:b2Shape=shapes[i] as b2Shape;
var inside:Boolean=tShape.TestPoint(tShape.GetBody().GetXForm(),mousePVec);
if (inside) {
body=tShape.GetBody();
break;
}
}
}
return body;
}
public function Update(e:Event):void {
m_world.Step(m_timeStep, m_iterations);
my_canvas.graphics.clear();
my_canvas.graphics.lineStyle(4,0x000000,1);
for (var j:b2Joint=m_world.GetJointList(); j; j=j.GetNext()) {
my_canvas.graphics.moveTo(j.GetAnchor1().x*30,j.GetAnchor1().y*30);
my_canvas.graphics.lineTo(j.GetAnchor2().x*30,j.GetAnchor2().y*30);
}
}
}
}
更多精彩
赞助商链接