svg translate 操作

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		function dragElement(evt) {
            var target = evt.target;
            var id = target.id;
            var dx = evt.dx, dy = evt.dy;
            var scale = svgcanvas.scale();
            
            var transformBaseVal = target.transform.baseVal;
            
            if(transformBaseVal.numberOfItems == 0){
                var transformObject = svgRoot.createSVGTransform();
                transformBaseVal.appendItem(transformObject);
            }
            
            var transformItem = transformBaseVal.getItem(0);
            var transformMatrix = transformItem.matrix;
            
            var ox = transformMatrix.e, oy = transformMatrix.f;
    
            var x = ox + dx / scale, y = oy + dy / scale;
    
            log("scale:" + scale + ",offset:" + dx / scale + "," + dy / scale);
    
            transformItem.setTranslate(x,y);
        }
	}