return{x:xSum/positions.length,y:ySum/positions.length};},computeTouchSpan_(positions){let xMin=Number.MAX_VALUE;let yMin=Number.MAX_VALUE;let xMax=Number.MIN_VALUE;let yMax=Number.MIN_VALUE;for(let i=0;i<positions.length;++i){xMin=Math.min(xMin,positions[i].x);yMin=Math.min(yMin,positions[i].y);xMax=Math.max(xMax,positions[i].x);yMax=Math.max(yMax,positions[i].y);}
return Math.sqrt((xMin-xMax)*(xMin-xMax)+