Incorrect foregroundLayer frame

[markst]

The foregroundLayer frame is set using the frame of the button, which is an issue if the button's origin is non zero.

[markst]

private func prepareForegroundLayer() {
    foregroundLayer.frame = layer.frame

should be:

private func prepareForegroundLayer() {
    foregroundLayer.frame = layer.bounds

[markst]

or even better:

    override func layoutSublayersOfLayer(layer: CALayer) {
        super.layoutSublayersOfLayer(layer)

        foregroundLayer.frame = layer.bounds
    }