The DistanceJoint keeps the distance between 2 bodies constant. More...
| Import Statement: | import Felgo 4.0 |
| Inherits: |
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.
The following example shows how two physics bodies connected with a DistanceJoint are created every 4 seconds. The source code of the full example is provided in the distance folder of the Box2D Examples.
import QtQuick 2.0 import Felgo 4.0 GameWindow { // A heavy ball that will be created dynamically with the timer below Component { id: heavyBox EntityBase { property alias body: collider.body transformOrigin: Item.TopLeft width: 40 height: 40 BoxCollider { id: collider density: 0.005 friction: 0.3 restitution: 0.2 } Rectangle { anchors.fill: parent smooth: true color: "brown" } } } Component { id: lightBox EntityBase { property alias body: collider.body transformOrigin: Item.TopLeft width: 40 height: 40 BoxCollider { id: collider density: 0.002 friction: 0.3 restitution: 0.2 } Rectangle { anchors.fill: parent color: "red" } } } Component { id: extraJoint DistanceJoint { frequencyHz: 20 dampingRatio: 0.5 collideConnected: false } } // Timer that keeps creating heavy balls that crash down on the building Timer { running: true repeat: false interval: 2000 onTriggered: { // TODO: the body pos is not set to the entity pos initially, that is why the connecting is wrong when done dynamically! var ball1Id = entityManager.createEntityFromComponentWithProperties(heavyBox, { x: 400, y: 50}) var ball1 = entityManager.getEntityById(ball1Id) var ball2Id = entityManager.createEntityFromComponentWithProperties(lightBox, {x: 150, y: 50}) var ball2 = entityManager.getEntityById(ball2Id) var joint = extraJoint.createObject(world, { "bodyA": ball1.body, "bodyB": ball2.body, "world": world, "collideConnected": true }) } } Scene { id: scene PhysicsWorld { id: world anchors.fill: parent gravity.y: 9.81 } Wall { id: ground height: 20 anchors { left: parent.left; right: parent.right; top: parent.bottom } } Wall { id: ceiling height: 20 anchors { left: parent.left; right: parent.right; bottom: parent.top } } Wall { id: leftWall width: 20 anchors { right: parent.left; bottom: ground.top; top: ceiling.bottom } } Wall { id: rightWall width: 20 anchors { left: parent.right; bottom: ground.top; top: ceiling.bottom } } Ball { id: ball x: 100 y: 100 rotation: 0 radius: 20 } Square { id: square x: 220 y: 180 rotation: 0 width: 40 height: 40 } DistanceJoint { id: joint frequencyHz: 15 dampingRatio: 0.5 collideConnected: true bodyA: ball.body bodyB: square.body } MouseArea { anchors.fill: parent onClicked: { // "pull" the box towards the clicked position ball.body.applyLinearImpulse( Qt.point(20 * (mouseX - ball.x), 20 * (mouseY - ball.y)), ball.body.getWorldCenter()) } } } // end of Scene EntityManager { id: entityManager entityContainer: scene } }
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dampingRatio : real |
The damping ratio. 0 = no damping, 1 = critical damping. The default value is 0.
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frequencyHz : real |
The mass-spring-damper frequency in Hertz. The default value is 0.
Typically the frequency should be less than a half the frequency of the PhysicsWorld::timeStep. So if you are using a 60Hz time step, the frequency of the distance joint should be less than 30Hz. The reason is related to the Nyquist frequency.
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length : real |
The length between the 2 bodies, in pixels.
By default, it will be set to the distance between localAnchorA of Joint::bodyA and localAnchorB of Joint::bodyB.
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localAnchorA : point |
The local anchor point relative to the Joint::bodyA center in pixels.
The default is (0, 0), which means the center of Joint::bodyA.
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localAnchorB : point |
The local anchor point relative to the Joint::bodyB center in pixels.
The default is (0, 0), which means the center of Joint::bodyB.
Returns the reaction force, in kg*pixels/second^2 for a timestep of length inv_dt, in seconds.
For the Parameter inv_dt, World::timeStep can be used.
This is always 0, since a DistanceJoint only applies force and no torque.
For the Parameter inv_dt, World::timeStep can be used.
