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：
用html5绘制折线图的实例代码

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