RayCast

A RayCast object that reports when a ray hits a Fixture. More...

Import Statement:	import Felgo 4.0
Since:	Felgo 2.3.1
Inherits:	QtObject

List of all members, including inherited members

Properties

maxFraction : real

Signals

fixtureReported(Fixture fixture, point contactPoint, point contactNormal, real fraction)

Detailed Description

The RayCast object can be used to retrieve the fixtureReported signal of a World::rayCast() call.

Raycast Example

 import QtQuick 2.0
 import Felgo 4.0

 GameWindow {
   id: gameWindow
   screenWidth: 960
   screenHeight: 640

   Image {
     anchors.fill: parent
     source: "background.png"
   }

   Scene {
     id: scene
     width: 480
     height: 320

     PhysicsWorld {
       id: world
       debugDrawVisible: true
       gravity.y: 9.81
     } // end of PhysicsWorld

     Repeater {
       model: 4

       WoodenBox {
         x: Math.random() * (scene.width - 100) + 20
         y: Math.random() * (scene.height / 3) + 20
         rotation: Math.random() * 90
       }
     }

     Wall {
       id: ground
       height: 20
       anchors { left: parent.left; right: parent.right; bottom: parent.bottom }
     }
     Wall {
       id: ceiling
       height: 20
       anchors { left: parent.left; right: parent.right; top: parent.top }
     }
     Wall {
       id: leftWall
       width: 20
       anchors { left: parent.left; bottom: ground.top; top: ceiling.bottom }
     }
     Wall {
       id: rightWall
       width: 20
       anchors { right: parent.right; bottom: ground.top; top: ceiling.bottom }
     }

     //show the ray that is being cast as a rectangle
     Rectangle {
       property real mx: mouseArea.mouseX - scene.width / 2
       property real my: mouseArea.mouseY - scene.height / 2

       property real len: 2 * Math.sqrt(mx * mx + my * my)

       rotation: 180 / Math.PI * Math.atan2(my, mx)

       transformOrigin: Item.Center

       x: scene.width / 2 - len / 2
       y: scene.height / 2
       width: len
       height: 2
       color: "red"
     }

     //highlight the object which is hit by the ray
     Rectangle {
       id: rect
       property Item target: null
       width: target ? target.width : 0
       height: target ? target.height : 0
       x: target ? target.x : 0
       y: target ? target.y : 0
       color: "green"
       opacity: 0.5
       rotation: target ? target.rotation : 0
       visible: !!target
       transformOrigin: Item.TopLeft
     }

     RayCast {
       id: raycast
       maxFraction: 2 //cast ray twice the distance from start to end point
       onFixtureReported: (fixture, contactPoint, contactNormal, fraction) => {
         //fixture.getBody() returns the body object, body.target returns the entity which contains the body
         var body = fixture.getBody()
         var entity = body.target

         rect.target = entity
         maxFraction = 0 // cancel current raycast, report no more objects
       }
     }

     MouseArea {
       id: mouseArea
       anchors.fill: parent
       hoverEnabled: true

       onClicked: {
         rect.target = null

         raycast.maxFraction = 2

         //cast a ray from the mouse position through the center of the scene
         var from = Qt.point(mouse.x, mouse.y)
         var to = Qt.point(scene.width / 2, scene.height / 2)
         console.log("raycast", from, to)
         world.rayCast(raycast, from, to)
       }
     }
   } // end of Scene

   EntityManager {
     id: entityManager
   }
 }

See the folder examples/physics/box2d-examples/qml/raycast for the Wall and WoodenBox implementation and for the image resources.

Property Documentation

maxFraction : real

This property determines length of the cast ray, as fraction of the length between the points from and to. After fixtureReported is called, it gets set to the length of the ray where it hit the fixture. You can then change the value of maxFraction to a larger value, to query for more fixtures, or to a lower value to stop querying.

The default value is -1, which means default length between points from and to.

Signal Documentation

fixtureReported(Fixture fixture, point contactPoint, point contactNormal, real fraction)

This handler is called when the ray hits a Fixture after casting it with World::rayCast().

You can retrieve information of the collided fixture with the fixture argument. The contactPoint tells where the fixture has been hit, the contactNormal is the normal on the fixture.

The argument fraction tells the length of the ray, as a fraction of the length between the start and end point. This may also be greater than 1, if the maxFraction field has been set accordingly.

To get access to the collided entity, use this example code:

 import Felgo 4.0

 RayCast {
   id: raycast
   maxFraction: 2 //cast ray twice the distance from start to end point
   onFixtureReported: (fixture, contactPoint, contactNormal, fraction) => {
     console.debug("fixtureReported:", fixture)

     //fixture.getBody() returns the body object, body.target returns the entity which contains the body
     var body = fixture.getBody()
     var entity = body.target
     maxFraction = 0 // cancel current raycast, report no more objects
   }
 }

Note: The corresponding handler is onFixtureReported.

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