javascript - (Vue, ChartJS) Create gradient background for chart from child component canvas context - Stack Overflow

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I want to give my chart a gradient background color, but I can't access the canvas context as my chart gets rendered in a wrapper ponent I wrote.

What I want to achieve:

My actual wrapper rather looks like this:

<script>
import { Line, mixins } from "vue-chartjs";
const { reactiveProp } = mixins;

export default {
  extends: Line,
  mixins: [reactiveProp],
  props: ["options"],
  ponents: {},
  mounted() {
    // this.chartData is created in the mixin
    this.renderChart(this.chartData, this.options);
  }
};
</script>

I'm using my wrapper for different line charts and let it's parent pass down the relevant data - sometimes using the wrapper ponent several times per page.

All configuration (options, labels, etc.) gets done in the parent ponent, which uses the wrapper.

Is there a way to get the canvas context from the wrapper to the parent ponent, which uses the wrapper?

To create the gradient, you need something like this:

this.gradient = this.$refs.canvas
  .getContext("2d")
  .createLinearGradient(0, 0, 0, 450);

this.gradient.addColorStop(0, "rgba(255, 0,0, 0.5)");
this.gradient.addColorStop(0.5, "rgba(255, 0, 0, 0.25)");
this.gradient.addColorStop(1, "rgba(255, 0, 0, 0)");

..but this.$refs.canvas is undefined in the parent ponent, which prevents me from getting the context, so I can't create a gradient.

I want to give my chart a gradient background color, but I can't access the canvas context as my chart gets rendered in a wrapper ponent I wrote.

What I want to achieve:

My actual wrapper rather looks like this:

<script>
import { Line, mixins } from "vue-chartjs";
const { reactiveProp } = mixins;

export default {
  extends: Line,
  mixins: [reactiveProp],
  props: ["options"],
  ponents: {},
  mounted() {
    // this.chartData is created in the mixin
    this.renderChart(this.chartData, this.options);
  }
};
</script>

I'm using my wrapper for different line charts and let it's parent pass down the relevant data - sometimes using the wrapper ponent several times per page.

All configuration (options, labels, etc.) gets done in the parent ponent, which uses the wrapper.

Is there a way to get the canvas context from the wrapper to the parent ponent, which uses the wrapper?

To create the gradient, you need something like this:

this.gradient = this.$refs.canvas
  .getContext("2d")
  .createLinearGradient(0, 0, 0, 450);

this.gradient.addColorStop(0, "rgba(255, 0,0, 0.5)");
this.gradient.addColorStop(0.5, "rgba(255, 0, 0, 0.25)");
this.gradient.addColorStop(1, "rgba(255, 0, 0, 0)");

..but this.$refs.canvas is undefined in the parent ponent, which prevents me from getting the context, so I can't create a gradient.

• javascript
• vue.js
• vuejs2
• chart.js
• vue-chartjs

Share Improve this question Follow asked Jun 25, 2018 at 11:05 Bennett DamsBennett Dams 7,05366 gold badges2929 silver badges4848 bronze badges 1

• 1 hey, I'm trying achieve something similar, I have a doubt, how exactly do you pass this.gradient to your chartData object? – Gagan Ganapathy Ajjikuttira Commented Jul 21, 2020 at 14:54

Add a ment  | 

1 Answer 1

Sorted by: Reset to default 4

You can access this.$refs.canvas in your chart ponent. If you want to access it from your parent ponent there are several ways.

The fast unclean way is over this.$children https://v2.vuejs/v2/api/#vm-children

A better way would be to setup the gradient stuff into a own method and pass in all data as props to your chart ponent.

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