Unable to set different line colors based on marker values and color in chart js line graph

[ttvettuparambil]

Expected behavior

The line chart should render with the line color changing based on the marker colors.
This is an example screenshot of what the output should be.
https://pasteboard.co/6PKRCJzsaKa6.png
Currently the code that I have written using chart JS (v 4.2.1) is not rendering in the browser.
I am trying to do this using vanilla javascript. I am welcome to any suggestions. If there is an alternate method, kindly suggest it to me also.

Current behavior

The code is not rendering in the frontend and the there is error in console window. (screenshot attached below.)
https://pasteboard.co/Rma2XuY1jAz7.png

Reproducible sample

https://codepen.io/Thomas-1/pen/oNPVqQp

Optional extra steps/info to reproduce

No response

Possible solution

No response

Context

This is an example screenshot of what I am trying to achieve.
https://pasteboard.co/HgPrWMUziKIS.png

chart.js version

v4.2.1

Browser name and version

Microsoft Edge Version 111.0.1661.44 (Official build) (64-bit)

Link to your project

No response

[stockiNail]

@ttvettuparambil I think you could the segment option (instead of custom plugin) in line chart: https://www.chartjs.org/docs/latest/charts/line.html#segment

[stockiNail]

@ttvettuparambil another possible solution is to use chartjs-plugin-gradient.

[ttvettuparambil]

@ttvettuparambil I think you could the segment option (instead of custom plugin) in line chart: https://www.chartjs.org/docs/latest/charts/line.html#segment

Hello stockiNail, thank you for the reply. I have managed to use segments to bring colors in different segments but still have not gotten the required result.

currently I have modified my code as can be seen in the link below.
https://pastebin.com/JdFtjE4s

I am trying to use ctx object to access p0 and p1 points and give a gradient.addColorStop to p0 and p1 points so that theoretically the gradient should appear in each segment depending on the color of the points, but unfortunately let gradient = ctx.createLinearGradient(ctx.p0.x, ctx.p0.y, ctx.p1.x, ctx.p1.y) in test() is having an error in console although I can access p1 and p1 objects just fine.
Could you please take a look into the above pastebin url and see if I am missing anything. The chart designed using my code currently looks like this (screenshot attached below).
https://pasteboard.co/QoxILiee5MVP.png

[ttvettuparambil]

const test = (ctx) => {
// let gradient = ctx.createLinearGradient(ctx.p0.x, ctx.p0.y, ctx.p1.x, ctx.p1.y);
gradient.addColorStop(0, ctx.p0.options.backgroundColor);
gradient.addColorStop(1, ctx.p1.options.backgroundColor);
console.log(ctx p0 color::::>,ctx.p0.options.backgroundColor);
console.log(ctx p1 color::::>,ctx.p1.options.backgroundColor);
return gradient;
}
When I uncomment the first line in the function, I am getting "ctx.createLinearGradient is not a function" error in browser console. Could somebody tell me why it is like that.

[ttvettuparambil]

const test = (ctx) => {
// let gradient = ctx.createLinearGradient(ctx.p0.x, ctx.p0.y, ctx.p1.x, ctx.p1.y);
gradient.addColorStop(0, ctx.p0.options.backgroundColor);
gradient.addColorStop(1, ctx.p1.options.backgroundColor);
console.log(ctx p0 color::::>,ctx.p0.options.backgroundColor);
console.log(ctx p1 color::::>,ctx.p1.options.backgroundColor);
return gradient;
}
When I uncomment the first line in the function, I am getting "ctx.createLinearGradient is not a function" error in browser console. Could somebody tell me why it is like that.

[ttvettuparambil]

On logging the ctx object in console window for both segment{ borderColor } as well as datasets { borderColor } I have found that addcolorstop property is not available in segment{ borderColor }. So I guess segment method to add gradient for line is out of the question. Can you show me as to how to implement chartjs-plugin-gradient in vanilla js.
Also related question, how to make segment line color same as that of p1 point using segments ?

[ttvettuparambil]

I have found the solution (kind of.) Since gradient is not possible in ctx (context) object in borderColor in segments object, I decided to apply a solid color for each segment in the graph with the color changing based on the ctx.p1.options.backgroundColor value. This is the code that I have used to acheive this.
It now looks something like this.
https://pasteboard.co/EbJAm3uL4xji.png

function drawCustomScoreChart(panel) {
vals = setDataForReadinessScore()
var data = vals["y"];
console.log(data is:::::::>,data);
var colors = getReadinessScoreColors()
console.log(colors::::::::::>,colors);
const test = (ctx) => {
console.log(ctx object::::::>,ctx);
console.log(ctx p0 color::::>,ctx.p0.options.backgroundColor);
console.log(ctx p1 color::::>,ctx.p1.options.backgroundColor);
return ctx.p1.options.backgroundColor;
// return gradient;
}

  var myChart = new Chart(panel, {
    type: 'line',
    data: {
      labels: vals["x"],
      datasets: [{
        label: 'Sales',
        data: data,
        tension:0.4,
        borderColor:'#000',
        pointBackgroundColor:colors,
        borderWidth: 3,
        segment: {

            borderColor: ctx => test(ctx),

        }
      }],
     
    },
    options: {
        maintainAspectRatio: false,
    //   aspectRatio: 3/1,
      responsive: true,
      showScale: false,
      scales: {
        y: {
            beginAtZero: true
        },
        x: {
            beginAtZero:true
        },  
        yAxes: [{
          ticks: {
            beginAtZero: true
          }
        }],
      },
    //   extra code
    plugins: {
        legend: {
          display: false
        }
      },
    },
 
  });

}
I would like it if gradient option would be applied by default to chart.js library.

[ttvettuparambil]

@ttvettuparambil another possible solution is to use chartjs-plugin-gradient.

@stockiNail @can you give me a working example of this plugin along with a quick summary on the plugin options ?

[stockiNail]

On logging the ctx object in console window for both segment{ borderColor } as well as datasets { borderColor } I have found that addcolorstop property is not available in segment{ borderColor }. So I guess segment method to add gradient for line is out of the question. Can you show me as to how to implement chartjs-plugin-gradient in vanilla js. Also related question, how to make segment line color same as that of p1 point using segments ?

@ttvettuparambil apologize for late reply but I was busy on other stuff.
Well, the ctx that you are getting as argument is not the context of the canvas but the context of the scriptable option.
See the doc: https://www.chartjs.org/docs/latest/charts/line.html#segment

To have the canvas context, you should access to the chart instance, as following:

const canvasContext = ctx.chart.ctx;
canvasContext.createLineagGradient...

[stockiNail]

@ttvettuparambil another possible solution is to use chartjs-plugin-gradient.

@stockiNail @can you give me a working example of this plugin along with a quick summary on the plugin options ?

Yes, I can but let me take time a bit. But having a look to your code, I see (but maybe I'm wrong) that the gradient must be applied to the single segment and based on the values of p0 and p1, therefore the plugin is not a good solution for this use case because the plugin is applied to the whole line based on values of dataset.

[stockiNail]

const test = (ctx) => {
// let gradient = ctx.createLinearGradient(ctx.p0.x, ctx.p0.y, ctx.p1.x, ctx.p1.y);
gradient.addColorStop(0, ctx.p0.options.backgroundColor);
gradient.addColorStop(1, ctx.p1.options.backgroundColor);
console.log(ctx p0 color::::>,ctx.p0.options.backgroundColor);
console.log(ctx p1 color::::>,ctx.p1.options.backgroundColor);
return gradient;
}

I didn't test it but it should be:

const test = (context) => {
  const {chart, p0, p1} = context;
  const ctx = chart.ctx;
  let gradient = ctx.createLinearGradient(p0.x, p0.y, p1.x, p1.y);
  gradient.addColorStop(0, p0.options.backgroundColor);
  gradient.addColorStop(1, p1.options.backgroundColor);
  return gradient;
}

[ttvettuparambil]

const test = (ctx) => {
// let gradient = ctx.createLinearGradient(ctx.p0.x, ctx.p0.y, ctx.p1.x, ctx.p1.y);
gradient.addColorStop(0, ctx.p0.options.backgroundColor);
gradient.addColorStop(1, ctx.p1.options.backgroundColor);
console.log(ctx p0 color::::>,ctx.p0.options.backgroundColor);
console.log(ctx p1 color::::>,ctx.p1.options.backgroundColor);
return gradient;
}

Hello @stockiNail, Thank you for your response, Seems however the snippet is not working properly. I called the function in segment: { borderColor } and put the snippet but now it is rendering only green color gradient. This is the screenshot of the output now.
https://pasteboard.co/4VDXH8dIiBag.png
If you look at the screenshot, the first 2 points have orange color. The third one is having dark green color and the fourth point having green color, but the entire gradient line is having green color.

segment: {
borderColor: ctx => test(ctx),
}
const test = (context) => {
const {chart, p0, p1} = context;
const ctx = chart.ctx;
let gradient = ctx.createLinearGradient(p0.x, p0.y, p1.x, p1.y);
gradient.addColorStop(0, p0.options.backgroundColor);
gradient.addColorStop(1, p1.options.backgroundColor);
return gradient;
}

[ttvettuparambil]

@ttvettuparambil another possible solution is to use chartjs-plugin-gradient.

@stockiNail @can you give me a working example of this plugin along with a quick summary on the plugin options ?

Yes, I can but let me take time a bit. But having a look to your code, I see (but maybe I'm wrong) that the gradient must be applied to the single segment and based on the values of p0 and p1, therefore the plugin is not a good solution for this use case because the plugin is applied to the whole line based on values of dataset.

Ok thank you for clarifying this point for me.

[ttvettuparambil]

On logging the const ctx = chart.ctx; I dont see any p0 and p1 objects in the output. So I am not sure how the green gradient color is even rendering.