javascript - Chart.js — 绘制任意垂直线

Question

如何使用 Chart.js 在 x 轴上的特定点绘制垂直线？

特别是，我想在折线图上画一条线来指示当前日期。这是图表的模型: http://i.stack.imgur.com/VQDWR.png

Answer 1

更新 - 此答案适用于 Chart.js 1.x，如果您正在寻找 2.x 答案，请查看评论和其他答案。

您扩展折线图并在绘制函数中包含绘制线条的逻辑。

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预览

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HTML

<div>
    <canvas id="LineWithLine" width="600" height="400"></canvas>
</div>

脚本

var data = {
    labels: ["JAN", "FEB", "MAR", "APR", "MAY", "JUN", "JUL", "AUG", "SEP", "OCT", "NOV", "DEC"],
    datasets: [{
        data: [12, 3, 2, 1, 8, 8, 2, 2, 3, 5, 7, 1]
    }]
};

var ctx = document.getElementById("LineWithLine").getContext("2d");

Chart.types.Line.extend({
    name: "LineWithLine",
    draw: function () {
        Chart.types.Line.prototype.draw.apply(this, arguments);

        var point = this.datasets[0].points[this.options.lineAtIndex]
        var scale = this.scale

        // draw line
        this.chart.ctx.beginPath();
        this.chart.ctx.moveTo(point.x, scale.startPoint + 24);
        this.chart.ctx.strokeStyle = '#ff0000';
        this.chart.ctx.lineTo(point.x, scale.endPoint);
        this.chart.ctx.stroke();

        // write TODAY
        this.chart.ctx.textAlign = 'center';
        this.chart.ctx.fillText("TODAY", point.x, scale.startPoint + 12);
    }
});

new Chart(ctx).LineWithLine(data, {
    datasetFill : false,
    lineAtIndex: 2
});

选项属性 lineAtIndex 控制画线的点。

fiddle - http://jsfiddle.net/dbyze2ga/14/