Framebuffer hole digging test

digHole.qml

import QtQuick 2.1

Rectangle {
    height: 600
    width: 800
    color: "red"

    ShaderEffect {
        height: parent.height / 4
        width: parent.width / 4
        anchors.centerIn: parent
        blending: false
        fragmentShader:
            "uniform lowp float qt_Opacity;" +
            "void main() {" +
            "    gl_FragColor = vec4(0.0, 0.0, 0.0, 0.0);" +
            "}"
    }
}