html5绘制折线图

时间：2022-01-20 21:09:44

html5绘制折线图详细代码

<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)

			  {d=d-data[i];

				  }

				  else{d=data[i];};

            if (d > max_v) { max_v =d};

          }

          max_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：

html5绘制折线图

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