用html5绘制折线图的实例代码

(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>

用html5绘制折线图的实例代码

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