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RopeJoint

The RopeJoint restricts the maximum distance between two points. More...

• List of all members, including inherited members

Properties

• localAnchorA : point
• localAnchorB : point
• maxLength : real

Methods

• point getReactionForce(real inv_dt)
• real getReactionTorque(real inv_dt)

Detailed Description

The RopeJoint can be useful to prevent chains of bodies from stretching, even under high load. All 3 properties: bodyA, bodyB and maxLength need to be set to work properly.

The DistanceJoint connects two physics bodies with a joint that keeps the distance between these bodies constant. The anchor points are defined relative to the bodies' centers. If no length is specified, it is auto calculated by the distance between the two anchor points.

For a comprehensive documentation of all joints see the Box2D documentation at http://www.box2d.org/manual.html#_Toc258082974.

Example Usage

The following example shows how two physics bodies are connected with a RopeJoint. The 3 bodies are connected with 2 RopeJoints, which limits the maximum distance between 2 bodies. By clicking on the window, an impulse to the right can be applied to move the 2 lower bodies. The source code of the full example is provided in the rope folder of the Box2D Examples.

 import QtQuick 2.0
 import Felgo 4.0


 GameWindow {
   id: screen

   Scene {
     id: scene

     PhysicsWorld {
       id: world
       debugDrawVisible: true
       gravity.y: 10
     }

     Ball {
       id: ball1
       x: 200
       y: 30
       radius: 15
       // make this ball static, otherwise all would fall down
       // the second ball is connected to the first, and the third to the second
       bodyType: Body.Static
     }

     Square {
       id: square2
       x: 250
       y: 30
       width: 20
       height: 20
     }

     Ball {
       id: ball3
       x: 330
       y: 30
       radius: 10
     }

     RopeJoint {
       id: ropeJoint1
       // the initial distance between ball1 & ball2 is 50, so the rope is longer than the initial distance
       maxLength: 70
       bodyA: ball1.body
       bodyB: square2.body

       //anchors should be in the middle of the items
       localAnchorA: Qt.point(ball1.width/2, ball1.height/2)
       localAnchorB: Qt.point(square2.width/2, square2.height/2)
     }

     RopeJoint {
       id: ropeJoint2
       // the initial distance between ball2 & ball3 is 80, so the rope is longer than the initial distance
       maxLength: 100
       bodyA: square2.body
       bodyB: ball3.body

       //anchors should be in the middle of the items
       localAnchorA: Qt.point(square2.width/2, square2.height/2)
       localAnchorB: Qt.point(ball3.width/2, ball3.height/2)
     }

     Text {
       z: 1 // put on top of DebugDraw in QML renderer
       color: "blue"
       text: "Click to apply an impulse to the right on the green square in the middle"
     }

   } // end of Scene

   MouseArea {
     anchors.fill: parent
     onClicked: {
       square2.body.applyLinearImpulse(Qt.point(100, 0), square2.body.getWorldCenter())
     }
   }

   EntityManager {
     id: entityManager
   }

 }

Property Documentation

Method Documentation