EffectMagnify.qml Example File

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 import QtQuick 2.0

 Effect {
     id: root
     divider: false
     parameters: ListModel {
         ListElement {
             name: "radius"
             value: 0.5
         }
         ListElement {
             name: "diffraction"
             value: 0.5
         }
     }

     property real posX: -1
     property real posY: -1

     QtObject {
         id: d
         property real oldTargetWidth: root.targetWidth
         property real oldTargetHeight: root.targetHeight
     }

     // Transform slider values, and bind result to shader uniforms
     property real radius: parameters.get(0).value * 100
     property real diffractionIndex: parameters.get(1).value

     onTargetWidthChanged: {
         if (posX == -1)
             posX = targetWidth / 2
         else if (d.oldTargetWidth != 0)
             posX *= (targetWidth / d.oldTargetWidth)
         d.oldTargetWidth = targetWidth
     }

     onTargetHeightChanged: {
         if (posY == -1)
             posY = targetHeight / 2
         else if (d.oldTargetHeight != 0)
             posY *= (targetHeight / d.oldTargetHeight)
         d.oldTargetHeight = targetHeight
     }

     fragmentShaderFilename: "shaders/magnify.fsh"

     MouseArea {
         anchors.fill: parent
         onPositionChanged: { root.posX = mouse.x; root.posY = root.targetHeight - mouse.y }
     }
 }