code: function drawCanvasReady() {
          $drawBoard.context = $drawBoard.getContext('2d');
          var context = $drawBoard.context;
          context.lineWidth = 3;
          //context.lineCap = 'square'; //'round';
          context.lineJoin = 'round'; //'bevel';
          context.strokeStyle = 'rgba(255,0,0,0.5)'; //"red";
      }
docs: *********画图部分事件处理函数*********** 画图前准备