ChartJS取决于数据的不同背景渐变（折线图）

问题描述

我正在尝试使用ChartJS折线图创建类似如下的内容。我已经可以按需使用顶部渐变，但是我找不到能在数据值低于0时更改底部渐变的方法。

I am trying to create something that looks like this using ChartJS line graph. I've got the top gradient working as I want, I just cannot find a way to get the bottom gradient to change when my data value is below 0.

我我曾尝试根据我的数据使用一系列不同的背景颜色，并且尝试使用插件beforeDraw更改背景颜色（它将所有背景颜色都更改为相同的颜色）。

I've tried using an array of different background colors based on my data and I have tried using plugin beforeDraw to change the background color (it changed them all to the same color).

推荐答案

Chart.js问题似乎符合您的目标。 是使用。幸运的是， berosoboy已经这个。下面是一个工作示例。我已对其进行了少许修改，以删除对 window.myColors 的引用。

Chart.js issue #3071 Multiple fill colors for line chart seems to match your objective. The official response is to use a CanvasGradient. Fortunately, 'berosoboy' has posted an inline plugin to do this. A working example is included below. I've modified it slightly to remove references to window.myColors.

let posColour = 'rgba(0, 255, 0, .1)',
  negColour = 'rgba(255, 0, 0, .1)',
  myBarChart = new Chart(document.getElementById('chart'), {
    type: 'line',
    data: {
      labels: ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j'],
      datasets: [{
        label: 'Series1',
        data: [1, -1, 1, -1, 1, -1, 1, -1, 1, -1]
      }]
    },
    options: {
      maintainAspectRatio: false
    },
    // source: https://github.com/chartjs/Chart.js/issues/3071#issuecomment-371001496
    plugins: [{
      beforeRender: function(c, options) {
        var dataset = c.data.datasets[0];
        var yScale = c.scales['y-axis-0'];
        var yPos = yScale.getPixelForValue(0);

        var gradientFill = c.ctx.createLinearGradient(0, 0, 0, c.height);
        gradientFill.addColorStop(0, posColour);
        gradientFill.addColorStop(yPos / c.height - 0.01, posColour);
        gradientFill.addColorStop(yPos / c.height + 0.01, negColour);
        gradientFill.addColorStop(1, negColour);

        var model = c.data.datasets[0]._meta[Object.keys(dataset._meta)[0]].$filler.el._model;
        model.backgroundColor = gradientFill;
      }
    }]
  });

<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.2/Chart.min.js"></script>
<canvas id="chart"></canvas>

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