How to write customQML Text shader using distance field?

[Espoo]

As I know, Qml Text use distance field technique to render text. I wish i had direct acess to that distance field texture to achieve custom Text effect ,(I know that i can use layer mechanism and render Text to texture and then apply some effect but that's not what I want to achieve). How to do that?

        Text{
            id:test_text
            x:parent.width
            text: "Hello World!!"
            font.family: "Helvetica"
            font.bold: true
            font.pixelSize :parent.height*0.65
            color: "black"
            anchors.verticalCenter: parent.verticalCenter


            ShaderEffect {
                property variant source: ShaderEffectSource { sourceItem: test_text; hideSource: false }
                anchors.fill: parent

                fragmentShader: "

                    uniform sampler2D source;
                    varying highp vec2 qt_TexCoord0;

                    void main(void)
                    {
                        if(texture2D(source, qt_TexCoord0).a < 0.5)
                            gl_FragColor = vec4(1.0,1.0,0.0,0.000);
                    }
                "
            }
        }