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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
    }

    fragmentShaderSrc: "uniform sampler2D source;
                        uniform lowp float qt_Opacity;
                        varying vec2 qt_TexCoord0;
                        uniform float radius;
                        uniform float diffractionIndex;
                        uniform float targetWidth;
                        uniform float targetHeight;
                        uniform float posX;
                        uniform float posY;

                        void main()
                        {
                            vec2 tc = qt_TexCoord0;
                            vec2 center = vec2(posX, posY);
                            vec2 xy = gl_FragCoord.xy - center.xy;
                            float r = sqrt(xy.x * xy.x + xy.y * xy.y);
                            if (r < radius) {
                                float h = diffractionIndex * 0.5 * radius;
                                vec2 new_xy = r < radius ? xy * (radius - h) / sqrt(radius * radius - r * r) : xy;
                                vec2 targetSize = vec2(targetWidth, targetHeight);
                                tc = (new_xy + center) / targetSize;
                                tc.y = 1.0 - tc.y;
                            }
                            gl_FragColor = qt_Opacity * texture2D(source, tc);
                        }"

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