[Elisabeth]

Hello everyone,

 

when rotating an entity which includes a particle emitter, the movement of the emitted particles is influenced by the rotation of the entity. The effect becomes more obvious for fast rotation velocities. Here is some code which showcases the behaviour:

 

main.qml:

import Felgo 3.0
import QtQuick 2.0

GameWindow {
  id: gameWindow
  activeScene: scene
  width: 960
  height: 640

  EntityManager {
    id: entityManager
    entityContainer: scene
  }

  Scene {
    id: scene
    width: 480
    height: 320

    Item{
      BoxCollider {
    	  id: fix
    	  x: scene.width / 2
    	  y: scene.height / 2
    	  bodyType: Body.Static
      }

      ParticleEmitter {
      	  x: scene.width/2
      	  y: scene.height/2
      	  jointBody: fix.body
      }

      PhysicsWorld {
        id: world
        updatesPerSecondForPhysics: 60
        gravity.y: 0.0

        velocityIterations: 5
        positionIterations: 5

        running: true
      }
    }
  }// scene
}

ParticleEmitter.qml:

import QtQuick 2.0
import Felgo 3.0

EntityBase {
  id: root
  width: 40
  height: 10
  //transformOrigin: Item.TopLeft

  property variant jointBody: null
  property alias body: collider.body

  BoxCollider {
    id: collider
    width: root.width
    height: root.height
    x: -root.width / 2
    y: -root.height / 2

    density: 0.05

    torque: {
      0.01;
    }
 
    Rectangle {
      id: rect
      anchors.fill: parent
      color: "red"
    }
  }

  RevoluteJoint {
    id: joint
    bodyA: body
    bodyB: jointBody
    localAnchorA: Qt.point(-20, 0)
    world: physicsWorld
  }

  Particles{
    id: particles
    x: 20
  }
}

Particles.qml

import QtQuick 2.0
import Felgo 3.0

ParticleVPlay {
  id: particle
  fileName: "FireParticle.json"

  startParticleSize: 10
  startParticleSizeVariance: 0
  finishParticleSize: 10
  finishParticleSizeVariance: 0
  particleLifespan: 3

  positionType: ParticleVPlayBase.Free

  // start when finished loading
  autoStart: true
}

 

For the particles “FireParticle.json” and “particleFire.png” are used which are included in the ParticleEditor demo.

 

Any hint is highly appreciated!

Cheers,

Thomas

[AlexFelgo Team]

Hi Thomas,

we can reproduce the issue and are working on a fix for this. The problem is the following: For the Free positionType, the particle is internally compensating the movement of the parent. Now in your use case, the parent is only rotation, so the particle is taking care of this rotation change to compensate it. This would work fine if the particle would be emitted in the center of the rotating parent. Now that the particle is NOT in the center of the parent, but sitting on the edge instead, it still only sees the rotation change of the parent, and not that the particle itself is effectively also changing its x and y coordinates on the screen, due to sitting on the edge of the rotating parent. Therefore the exact movement of the particle emitter is not fully compensated.

A workaround for you would be to wrap the particle in a parent item that performs the movement by really changing its x and y values. This could look like this:
main.qml

// ...      
      ParticleEmitter {
          id: particleEmitter
          x: scene.width/2
          y: scene.height/2
          jointBody: fix.body
      }

      Item {
        x: particleEmitter.x + particleEmitter.width/2 * Math.cos(particleEmitter.rotation*Math.PI/180)
        y: particleEmitter.y + particleEmitter.width/2 * Math.sin(particleEmitter.rotation*Math.PI/180)
        rotation: particleEmitter.rotation
        Particles {
          id: particles
        }
      }
// ...

If you want to try standard Qt5 Particles instead, this is a nice set of tutorials, also containing one for Particles: http://qmlbook.org/ch08/index.html

Sorry for the inconvenience.

Cheers,
Alex

• This reply was modified 9 years, 8 months ago by  Alex.
• This reply was modified 9 years, 8 months ago by  Alex.