Infinite animations, where "from" and "to" are set based on chaning values

RudolfVonKrugstein

Hey,

I am atempting to animated the BusyIndicator of the material design like here: https://material-design.storage.googleapis.com/publish/material_v_4/material_ext_publish/0B6Okdz75tqQsemFpeElQMFBSMG8/061101_Circular_Sheet_xhdpi_004.webm

For this I need want to animate the "start" end "end" Angles of a circle arc. The animation should be like this (in a sequential animation):

Animate the start angle from its current value to endAngle+2*M.PI - offset
Animate the end angle form its current value to startAngle
Loop

So I am doing this (arc is the object drawing the circle arc on a canvas):

 SequentialAnimation {
            running: control.visible == true
            loops: Animation.Infinite
            RotationAnimation {
                target: arc
                property: "startAngle_"
                from: arc.startAngle_
                to: arc.endAngle_ + 2*Math.PI * 7.0/8.0
                duration: 5000
                easing.type: Easing.InOutQuad
            }
            RotationAnimation {
                target: arc
                property: "endAngle_"
                from: arc.endAngle_
                to: arc.startAngle_
                duration: 5000
                easing.type: Easing.InOutQuad
            }
        }
}

Now it seems that the "to" and "from" values are taking from the moment the outer SequentialAnimation starts, not the moment the individual animation starts.

How can I change this?
Or, can I define an animation that animates to a value relative the current value at the moment the animation starts?

Thanks!
Nathan