用html5绘制折线图的实例代码

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<html>
<canvas id="a_canvas" width="1000" height="700"></canvas>
<script>
               (function (){    
        window.addEventListener("load", function(){    
          var data = [100,-1000,0,700];    
          // 获取上下文    
          var a_canvas = document.getElementById('a_canvas');    
          var context = a_canvas.getContext("2d");    
          // 绘制背景    
          var gradient = context.createLinearGradient(0,0,0,300);    
         // gradient.addColorStop(0,"#e0e0e0");    
          //gradient.addColorStop(1,"#ffffff");    
          context.fillStyle = gradient;    
          context.fillRect(0,0,a_canvas.width,a_canvas.height);    
          // 描绘边框    
          var grid_cols = data.length + 1;    
          var grid_rows = 4;    
          var cell_height = a_canvas.height / grid_rows;    
          var cell_width = a_canvas.width / grid_cols;    
          context.lineWidth = 1;    
          context.strokeStyle = "#a0a0a0";    
          // 结束边框描绘    
          context.beginPath();    
          // 准备画横线    
         /*for (var col = 0; col <= grid_cols; col++) {    
            var x = col * cell_width;    
            context.moveTo(x,0);    
            context.lineTo(x,a_canvas.height);    
          }    
          // 准备画竖线    
          for(var row = 0; row <= grid_rows; row++){    
            var y = row * cell_height;    
            context.moveTo(0,y);    
            context.lineTo(a_canvas.width, y);    
          }*/    
            //划横线    
            context.moveTo(0,a_canvas.height/2);    
            context.lineTo(a_canvas.width,a_canvas.height/2);    
            //画竖线    
          context.moveTo(0,0);    
            context.lineTo(0,a_canvas.height);    
          context.lineWidth = 1;    
          context.strokeStyle = "#c0c0c0";    
          context.stroke();    
          var max_v =0;    
          for(var i = 0; i<data.length; i++){    
              var d=0;    
              if(data[i]<0)    
              {dd=d-data[i];    
                  }    
                  else{d=data[i];};    
            if (d > max_v) { max_v =d};    
          }    
          max_vmax_v = max_v * 1.1;    
          // 将数据换算为坐标    
          var points = [];    
          for( var i=0; i < data.length; i++){    
            var v= data[i];    
            var px = cell_width *　(i +1);    
            var py = a_canvas.height/2 - a_canvas.height*(v / max_v)/2;    
            points.push({"x":px,"y":py});    
          }    
          // 绘制折现    
          context.beginPath();    
          context.moveTo(points[0].x, points[0].y);    
          for(var i= 1; i< points.length; i++){    
            context.lineTo(points[i].x,points[i].y);    
          }    
          context.lineWidth = 2;    
          context.strokeStyle = "#8BA9FF";    
          context.stroke();    
          //绘制坐标图形    
          for(var i in points){    
            var p = points[i];    
            context.beginPath();    
            context.arc(p.x,p.y,4,0,2*Math.PI);    
            //实心圆    
           /*    
            context.fillStyle = "#000";*/    
            //空心圆    
            context.strokeStyle = "#000";    
            context.stroke();    
            context.fillStyle="white";    
            context.fill();    
          }    
          //添加文字    
          for(var i in points)    
          {  var p = points[i];    
            context.beginPath();    
            context.fillStyle="black";    
            context.fillText(data[i], p.x + 1, p.y - 15);    
              }    
        },false);    
      })();    
</script>
</html>
运行结果如下：