时间戳

首页 > 解决方案 > 如何根据图表js中的值使用段属性为线条/边框颜色着色？

javascript - 如何根据图表js中的值使用段属性为线条/边框颜色着色？

问题描述

我正在尝试根据值创建具有不同颜色的线条/边框颜色的图表，例如此图像，因此颜色会在某个点上方和下方发生变化。

在此处输入图像描述

我已经浏览了 chartjs 文档（https://www.chartjs.org/docs/latest/samples/line/segments.html）上的片段示例，但这是使用跳过和点，而我正在尝试这样做具有价值，我无法弄清楚。

这是我的代码，它在 ejs 文件中（只有来自 js 的差异是通过 ${} 传入 <%- %> 的变量）：

<canvas id="LineChart" height="100"></canvas>

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/3.5.0/chart.min.js"
    integrity="sha512-asxKqQghC1oBShyhiBwA+YgotaSYKxGP1rcSYTDrB0U6DxwlJjU59B67U8+5/++uFjcuVM8Hh5cokLjZlhm3Vg=="
    crossorigin="anonymous" referrerpolicy="no-referrer"></script>
<script src="https://cdn.jsdelivr.net/npm/chartjs-plugin-datalabels@2"></script>


<script>
var ctx=document.getElementById( 'LineChart' ).getContext( "2d" );

var myChart=new Chart( ctx, {
                type: 'line',
                data: {
                    labels: <%- JSON.stringify( labels )%>,
                    datasets: [ {
                        label: ['a','b','c','d'],
                        data: ['1','2','3','4'],
                        backgroundColor:'rgba(54, 162, 235, 0.5)',
                        borderColor: rgb( 255, 255, 255 ), 
                        segment: {
                           borderColor: function black() {
                               if ( <%=maxValue%> >99) {
                                     return 'black';
                                 }
                             if ( <%=minValue%> >99) {
                                 return 'red';
                             }
                        }
                    },
}],
}
});
</script>

这是chartjs网站上的相关示例代码，（供快速参考）：

const skipped = (ctx, value) => ctx.p0.skip || ctx.p1.skip ? value : undefined;

const down = (ctx, value) => ctx.p0.parsed.y > ctx.p1.parsed.y ? value : undefined;

borderColor: ctx => skipped(ctx, 'rgb(0,0,0,0.2)') || down(ctx, 'rgb(192,75,75)')

我将非常感谢任何帮助！非常感谢。

更新：我大部分都可以解决这个问题（我可以制作一个线性渐变，颜色停止在某个值上），但我面临的问题是选择 x/y 轴来获取像素值，因为我不能正确选择图表，我在遇到问题的地方发表了评论，如果有人可以看一下并建议我一些东西，那将是很大的帮助，这里是小提琴：jsfiddle.net/baozkrw1/1

另外，这里是快速查看的小提琴代码：

HTML：

<h1>Chart One</h1>
<canvas id="LineChart" height="100"></canvas>

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/3.5.0/chart.min.js"
    integrity="sha512-asxKqQghC1oBShyhiBwA+YgotaSYKxGP1rcSYTDrB0U6DxwlJjU59B67U8+5/++uFjcuVM8Hh5cokLjZlhm3Vg=="
    crossorigin="anonymous" referrerpolicy="no-referrer"></script>
<script src="https://cdn.jsdelivr.net/npm/chartjs-plugin-datalabels@2"></script>

JS：

var ctx = document.getElementById('LineChart').getContext("2d");
let width, height, gradient;

function getGradient(ctx, chartArea) {
  const chartWidth = chartArea.right - chartArea.left;
  const chartHeight = chartArea.bottom - chartArea.top;

  if (gradient === null || width !== chartWidth || height !== chartHeight) {
    width = chartWidth;
    height = chartHeight;
    let y = 27; // I want this to be the pixel for value I pass, instead of hard value

    // but I can't select y-axis like this:
    // var yaxis=y.scales[ 'y-axis-0' ];
    // as it says undefined, and if I do like this : 
    //  const { ctx, canvas, scales: { x, y } }=chart;
    // var xaxis=x.scales[ 'x-axis-0' ];
    // It says chart not defined, which I think is because I am not making this a function and passing chart, and I can't figure out how to do it right.


    gradient = ctx.createLinearGradient(0, chartArea.bottom, 0, chartArea.top);
    gradient.addColorStop(y / chartHeight, 'black');
    gradient.addColorStop(0.6, 'yellow');

    gradient.addColorStop(0.9, 'red');

    gradient = ctx.createLinearGradient(0, chartArea.bottom, 0, chartArea.top);
    gradient.addColorStop(y / chartHeight, 'black');
    gradient.addColorStop(0.6, 'yellow');

    gradient.addColorStop(0.9, 'red');
  }
  return gradient;
}
var myChart = new Chart(ctx, {
  type: 'line',
  data: {
    labels: ['10', '20', '30', '40', '50'],
    datasets: [{
      label: 'Hello',
      data: ['1', '2', '3', '4', '5'],
      backgroundColor: 'rgba(255, 255, 78, 1)',
      borderColor: function(context, options) {
        const chart = context.chart;
        const {
          ctx,
          chartArea
        } = chart;
        if (!chartArea) {
          return null;
        }
        return getGradient(ctx, chartArea);
      },
    }]
  },
});

标签： javascriptnode.jschartschart.js

解决方案

您将获得函数正在评估的线段的起点和终点的两个点，p0在p1这里您可以像这样访问 y 值：val = ctx.p0.parsed.y;

现场示例：

var options = {
  type: 'line',
  data: {
    labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange"],
    datasets: [{
      label: '# of Votes',
      data: [12, 19, 3, 5, 2, 3],
      segment: {
        borderColor: (ctx) => {
          val = ctx.p0.parsed.y;
          return val >= 15 ? 'green' : val >= 10 ? 'blue' : val >= 5 ? 'pink' : 'purple'
        }
      }
    }]
  },
  options: {}
}

var ctx = document.getElementById('chartJSContainer').getContext('2d');
new Chart(ctx, options);
<body>
  <canvas id="chartJSContainer" width="600" height="400"></canvas>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/3.5.0/chart.js"></script>
</body>

编辑：

根据我的评论，您与您的 非常接近pixelForValue，您只需要将上下文也传递给您的渐变函数，并且不要使用 v2 默认 ID 来进行比例尺：

borderColor: function(context, options) {
  const chart = context.chart;
  const {
    ctx,
    chartArea
  } = chart;
  if (!chartArea) {
    return null;
  }
  return getGradient(ctx, chartArea, chart);
}

function getGradient(ctx, chartArea, chart) {
  const chartWidth = chartArea.right - chartArea.left;
  const chartHeight = chartArea.bottom - chartArea.top;

  if (gradient === null || width !== chartWidth || height !== chartHeight) {
    width = chartWidth;
    height = chartHeight;
    let y2 = 27; // I want this to be the pixel for value I pass, instead of hard value
    
    const { scales: { x, y } } = chart;

    console.log(x.getPixelForValue(20), x.getPixelForValue(4))
    


    gradient = ctx.createLinearGradient(0, chartArea.bottom, 0, chartArea.top);
    gradient.addColorStop(y2 / chartHeight, 'black');
    gradient.addColorStop(0.6, 'yellow');

    gradient.addColorStop(0.9, 'red');

    gradient = ctx.createLinearGradient(0, chartArea.bottom, 0, chartArea.top);
    gradient.addColorStop(y2 / chartHeight, 'black');
    gradient.addColorStop(0.6, 'yellow');

    gradient.addColorStop(0.9, 'red');
  }
  return gradient;
}

但是您也可以选择使用值和颜色制作一组对象，并使用它来制作渐变：

var ctx = document.getElementById('LineChart').getContext("2d");
let width, height, gradient;

const getcolorStop = (val, max) => (val / max);
const colors = [{
    val: 2,
    color: 'pink',
  },
  {
    val: 12,
    color: 'purple',
  },
  {
    val: 20,
    color: 'green',
  }
]

function getGradient(ctx, chartArea, chart) {
  const chartWidth = chartArea.right - chartArea.left;
  const chartHeight = chartArea.bottom - chartArea.top;

  if (gradient === null || width !== chartWidth || height !== chartHeight) {
    width = chartWidth;
    height = chartHeight;

    const {
      scales: {
        y: {
          max
        }
      }
    } = chart;

    gradient = ctx.createLinearGradient(0, chartArea.bottom, 0, chartArea.top);

    colors.forEach((color) => {
      if (color.val > max) {
        color.val = max;
      }

      gradient.addColorStop(getcolorStop(color.val, max), color.color);
    });
  }
  return gradient;
}
var myChart = new Chart(ctx, {
  type: 'line',
  data: {
    labels: ['10', '20', '30', '40', '50'],
    datasets: [{
      label: 'Hello',
      data: [12, 19, 3, 5, 2, 3],
      backgroundColor: 'rgba(255, 255, 78, 1)',
      borderColor: function(context, options) {
        const chart = context.chart;
        const {
          ctx,
          chartArea
        } = chart;
        if (!chartArea) {
          return null;
        }
        return getGradient(ctx, chartArea, chart);
      },
    }]
  },
});
<h1>Chart One</h1>
<canvas id="LineChart" height="100"></canvas>

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/3.5.0/chart.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/chartjs-plugin-datalabels@2"></script>

推荐阅读