[Vlad]

Any idea how to implement subject?

any tips?

 

thanks

[AlexFelgo Team]

Hi,

could you give us a little more details on which exact behavior you want to achieve? Something like a slingshot, or is it 2 objects that are connected with an elastic tape or anything else?
Cheers, Alex

[Vlad]

Hi Alex

Thanks for your answer

I can imagine something like rubber whip

 

br,

Vlad

[AlexFelgo Team]

And i guess you don’t only need a rubber whip animation, like you can make with a SpriteSequenceFromFile?

If you need the whole whip to have correct physical detection along the whole length, you can try connecting many small entities with RopeJoints in combination with other Joints. Have a look at http://felgo.com/doc/vplay-group.html#physics-components

In the following example i created a very raw version of an elastic rope (just the physics part, with just a few entities, and not very elegant 😉 )

Part.qml

import QtQuick 1.1
import VPlay 1.0
import Box2D 1.0

EntityBase {
  id: entity
  entityType: "part"

  property alias color: rectangle.color
  property alias bodyType: collider.bodyType
  property alias body: collider.body
  property alias partWidth: rectangle.width
  property alias partHeight: rectangle.height

  Rectangle {
    id: rectangle
    width: 5
    height: 5
    color: "blue"
  }

  BoxCollider {
    id: collider
    anchors.fill: rectangle
    friction: 0.2
    restitution: 0.2
    density: 5
    sleepingAllowed: false
    fixedRotation: true
  }
}

main.qml

import QtQuick 1.1
import VPlay 1.0
import Box2D 1.0

GameWindow {
  id: screen

  EntityManager {
    id: entityManager
  }

  Scene {
    id: scene
    PhysicsWorld {
      id: world
      gravity.y: -9.81
    }

    Part {id: part1; x: 200; y: 100
      color: "red"
      bodyType: Body.Static
    }
    Part {id: part2; x: 215; y: 100}
    Part {id: part3; x: 230; y: 100}
    Part {id: part4; x: 245; y: 100}
    Part {id: part5; x: 260; y: 100}
    Part {id: part6; x: 275; y: 100}
    Part {id: part7; x: 290; y: 100}
    Part {id: part8; x: 305; y: 100
      color: "red"
      partWidth: 20
      partHeight: 20
    }

    // connect each part to the following
    RopeJoint {
      id: ropeJoint1
      maxLength: 15
      bodyA: part1.body
      bodyB: part2.body
      world: world
      localAnchorA: Qt.point(part1.width/2, part1.height/2)
      localAnchorB: Qt.point(part2.width/2, part2.height/2)
    }
    RopeJoint {
      id: ropeJoint2
      maxLength: 15
      bodyA: part2.body
      bodyB: part3.body
      world: world
      localAnchorA: Qt.point(part2.width/2, part2.height/2)
      localAnchorB: Qt.point(part3.width/2, part3.height/2)
    }
    RopeJoint {
      id: ropeJoint3
      maxLength: 15
      bodyA: part3.body
      bodyB: part4.body
      world: world
      localAnchorA: Qt.point(part3.width/2, part3.height/2)
      localAnchorB: Qt.point(part4.width/2, part4.height/2)
    }
    RopeJoint {
      id: ropeJoint4
      maxLength: 15
      bodyA: part4.body
      bodyB: part5.body
      world: world
      localAnchorA: Qt.point(part4.width/2, part4.height/2)
      localAnchorB: Qt.point(part5.width/2, part5.height/2)
    }
    RopeJoint {
      id: ropeJoint5
      maxLength: 15
      bodyA: part5.body
      bodyB: part6.body
      world: world
      localAnchorA: Qt.point(part5.width/2, part5.height/2)
      localAnchorB: Qt.point(part6.width/2, part6.height/2)
    }
    RopeJoint {
      id: ropeJoint6
      maxLength: 15
      bodyA: part6.body
      bodyB: part7.body
      world: world
      localAnchorA: Qt.point(part6.width/2, part6.height/2)
      localAnchorB: Qt.point(part7.width/2, part7.height/2)
    }
    RopeJoint {
      id: ropeJoint7
      maxLength: 15
      bodyA: part7.body
      bodyB: part8.body
      world: world
      localAnchorA: Qt.point(part7.width/2, part7.height/2)
      localAnchorB: Qt.point(part8.width/2, part8.height/2)
    }

    // maximum length of whole rope, by making a RopeJoint between the first and the last Part
    RopeJoint {
      id: ropeJoint8
      maxLength: 200 //maximum lenght of streched rope will be 200 now
      bodyA: part1.body
      bodyB: part8.body
      world: world
      localAnchorA: Qt.point(part1.width/2, part1.height/2)
      localAnchorB: Qt.point(part2.width/2, part2.height/2)
    }

    Component {
      id: mouseJoint
      MouseJoint {
        maxForce: 5000
        dampingRatio: 1
        frequencyHz: 2
      }
    }

    MouseArea {
      anchors.fill: parent

      property Body selectedBody: null
      property MouseJoint mouseJointWhileDragging: null

      onPressed: {

        selectedBody = physicsWorld.bodyAt(Qt.point(mouseX, mouseY));
        console.debug("selected body at position", mouseX, mouseY, ":", selectedBody);
        // if the user selected a body, this if-check is true
        if(selectedBody) {
          // create a new mouseJoint
          mouseJointWhileDragging = mouseJoint.createObject(physicsWorld)

          // set the target position to the current touch position (initial position)
          mouseJointWhileDragging.targetPoint = Qt.point(mouseX, mouseY)

          // connect the joint with the body
          mouseJointWhileDragging.movingBody = selectedBody

          // set the physicsWorld where the joint should be created
          mouseJointWhileDragging.world = world
        }
      }

      onPositionChanged: {
        // this check is necessary, because the user might also drag when no initial body was selected
        if (mouseJointWhileDragging)
          mouseJointWhileDragging.targetPoint = Qt.point(mouseX, mouseY)
      }
      onReleased: {
        // if the user releases the body, remove the created MouseJoint
        if(selectedBody) {
          selectedBody = null
          if (mouseJointWhileDragging)
            mouseJointWhileDragging.destroy()
        }
      }
    }
  } // end of Scene
}

I hope this helps you. Of course achieving a realistic looking rubber whip with physically correct behavior and collision detection will be tricky.

Let me know if you have further questions!

Cheers, Alex

 

 

[Vlad]

Thanks, Alex!