function drawPreparedRoundCorner(ctx, roundCorner) {
  if (roundCorner.radius === 0) ctx.lineTo(roundCorner.cx, roundCorner.cy);else ctx.arc(roundCorner.cx, roundCorner.cy, roundCorner.radius, roundCorner.startAngle, roundCorner.endAngle, roundCorner.counterClockwise);
}
Draw corner provided by {@link getRoundCorner}

@param ctx :CanvasRenderingContext2D
@param roundCorner {{cx:number, cy:number, radius:number, endAngle: number, startAngle: number, counterClockwise: boolean}}