Chart.js：使用maxTicksLimit时均匀分布刻度 [英] Chart.js: evenly distribute ticks when using maxTicksLimit

问题描述

我使用Chart.js版本2.1.3制作折线图。

I made a line chart using Chart.js version 2.1.3.

        var canvas = $('#gold_chart').get(0);
        var ctx = canvas.getContext('2d');
        var fillPatternGold = ctx.createLinearGradient(0, 0, 0, canvas.height);
        fillPatternGold.addColorStop(0, '#fdca55');
        fillPatternGold.addColorStop(1, '#ffffff');

        var goldChart = new Chart(ctx, {
            type: 'line',
            animation: false,
            data: {
                labels: dates,
                datasets: [{
                    label: '',
                    data: prices,
                    pointRadius: 0,
                    borderWidth: 1,
                    borderColor: '#a97f35',
                    backgroundColor: fillPatternGold
                }]
            },
            title: {
                position: 'bottom',
                text: '\u7F8E\u5143 / \u76CE\u53F8'
            },
            options: {
                legend: {
                    display: false
                },
                tooltips: {
                    callback: function(tooltipItem) {
                        return tooltipItem.yLabel;
                    }
                },
                scales: {
                    xAxes: [{
                        ticks: {
                            maxTicksLimit: 8
                        }
                    }]
                }
            }
        });

输出结果如下：

如您所见，我通过 maxTicksLimit 。但是，分布不均匀。如何让滴答均匀分布？

As you can see, I limited the maximum count of ticks to 8 via maxTicksLimit. However, the distribution is not even. How can I make the ticks distribute evenly?

p.s。数据集中总有289条记录，每5分钟记录一次数据。 价格变量的样本值为：

p.s. there are always 289 records in the dataset, and the data is recorded every 5 minutes. Sample values of prices variable are:

[
  {"14:10", 1280.3},
  {"14:15", 1280.25},
  {"14:20", 1282.85}
]

我尝试了不同的 maxTicksLimit 值，但结果仍未均匀分配。

I tried different values of maxTicksLimit, and the results are still not distributed evenly.

推荐答案

Chart.js使用整数 skipRatio （计算出有多少要跳过的标签）。使用Chart.js v2.1.x，您可以编写自己的插件以使用小数skipRatio

Chart.js uses an integral skipRatio (to figure out how many labels to skip). With Chart.js v2.1.x, you can write your own plugin to use a fractional skipRatio

预览

脚本

Chart.pluginService.register({
    afterUpdate: function (chart) {
        var xScale = chart.scales['x-axis-0'];
        if (xScale.options.ticks.maxTicksLimit) {
            // store the original maxTicksLimit
            xScale.options.ticks._maxTicksLimit = xScale.options.ticks.maxTicksLimit;
            // let chart.js draw the first and last label
            xScale.options.ticks.maxTicksLimit = (xScale.ticks.length % xScale.options.ticks._maxTicksLimit === 0) ? 1 : 2;

            var originalXScaleDraw = xScale.draw
            xScale.draw = function () {
                originalXScaleDraw.apply(this, arguments);

                var xScale = chart.scales['x-axis-0'];
                if (xScale.options.ticks.maxTicksLimit) {
                    var helpers = Chart.helpers;

                    var tickFontColor = helpers.getValueOrDefault(xScale.options.ticks.fontColor, Chart.defaults.global.defaultFontColor);
                    var tickFontSize = helpers.getValueOrDefault(xScale.options.ticks.fontSize, Chart.defaults.global.defaultFontSize);
                    var tickFontStyle = helpers.getValueOrDefault(xScale.options.ticks.fontStyle, Chart.defaults.global.defaultFontStyle);
                    var tickFontFamily = helpers.getValueOrDefault(xScale.options.ticks.fontFamily, Chart.defaults.global.defaultFontFamily);
                    var tickLabelFont = helpers.fontString(tickFontSize, tickFontStyle, tickFontFamily);
                    var tl = xScale.options.gridLines.tickMarkLength;

                    var isRotated = xScale.labelRotation !== 0;
                    var yTickStart = xScale.top;
                    var yTickEnd = xScale.top + tl;
                    var chartArea = chart.chartArea;

                    // use the saved ticks
                    var maxTicks = xScale.options.ticks._maxTicksLimit - 1;
                    var ticksPerVisibleTick = xScale.ticks.length / maxTicks;

                    // chart.js uses an integral skipRatio - this causes all the fractional ticks to be accounted for between the last 2 labels
                    // we use a fractional skipRatio
                    var ticksCovered = 0;
                    helpers.each(xScale.ticks, function (label, index) {
                        if (index < ticksCovered)
                            return;

                        ticksCovered += ticksPerVisibleTick;

                        // chart.js has already drawn these 2
                        if (index === 0 || index === (xScale.ticks.length - 1))
                            return;

                        // copy of chart.js code
                        var xLineValue = this.getPixelForTick(index);
                        var xLabelValue = this.getPixelForTick(index, this.options.gridLines.offsetGridLines);

                        if (this.options.gridLines.display) {
                            this.ctx.lineWidth = this.options.gridLines.lineWidth;
                            this.ctx.strokeStyle = this.options.gridLines.color;

                            xLineValue += helpers.aliasPixel(this.ctx.lineWidth);

                            // Draw the label area
                            this.ctx.beginPath();

                            if (this.options.gridLines.drawTicks) {
                                this.ctx.moveTo(xLineValue, yTickStart);
                                this.ctx.lineTo(xLineValue, yTickEnd);
                            }

                            // Draw the chart area
                            if (this.options.gridLines.drawOnChartArea) {
                                this.ctx.moveTo(xLineValue, chartArea.top);
                                this.ctx.lineTo(xLineValue, chartArea.bottom);
                            }

                            // Need to stroke in the loop because we are potentially changing line widths & colours
                            this.ctx.stroke();
                        }

                        if (this.options.ticks.display) {
                            this.ctx.save();
                            this.ctx.translate(xLabelValue + this.options.ticks.labelOffset, (isRotated) ? this.top + 12 : this.options.position === "top" ? this.bottom - tl : this.top + tl);
                            this.ctx.rotate(helpers.toRadians(this.labelRotation) * -1);
                            this.ctx.font = tickLabelFont;
                            this.ctx.textAlign = (isRotated) ? "right" : "center";
                            this.ctx.textBaseline = (isRotated) ? "middle" : this.options.position === "top" ? "bottom" : "top";
                            this.ctx.fillText(label, 0, 0);
                            this.ctx.restore();
                        }
                    }, xScale);
                }
            };
        }
    },
});

---

小提琴 - http://jsfiddle.net/bh63pe1v/

这篇关于Chart.js：使用maxTicksLimit时均匀分布刻度的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！