用html5绘制折线图的实例代码
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2022-05-04 22:14:08
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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：
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