Snap SVG围绕某个点旋转元素

Question

我在SVG中有轮盘赌和球。轮盘旋转，我想围绕轮盘赌中心旋转球。但它围绕其他点旋转。如何围绕轮盘中心旋转？

var bbox = ballg.getBBox(); //bounding box, get coords and centre
var scale = 2.85;
var off = 10;
ballAnimation(bbox.cx + off, bbox.cy + off, 3000, scale);

function ballAnimation(cx, cy, speed, scale){
    ballg.attr({ transform: 'r0 ' + cx + ' ' + cy + " s" + scale + "," + scale + "," + cx + "," + cy }); //Reset + Scale setup
    ballg.stop(true).animate(
        { transform: "r360," + cx + ',' + cy + " s" + scale + "," + scale + "," + cx + "," + cy },
        speed,
        function(){
            ballAnimation(cx,cy, speed, scale);
        }
    );
}

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