Rendering / Returning HTML5 Canvas in ReactJS

react hooks + canvas
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I am trying to render a canvas using React. The graphics inside the canvas would also be handled by Reacts render method.

The current code does render a canvas with the graphics I want. But I am looking for a way to return a canvas with my graphics from within the render method. The reason I want this, is cause I want this to work in "React Way".

Ideally, I would want my code to be something like this:

return(
  <div>
    <canvas id='my_canvas_with_graphics_rendered_in_react'></canvas>
  </div>
);

First, I want to know if this is even possible. Or if I should look for an alternative.

Maybe Im missing the point of React, if that is the case please let me know. I do hope there is a solution, because from what I've read React touts itself as the V in MVC. That is why, if possible, this would be a perfect solution for what I'm trying to do. I would not have to worry about the rendering inside my canvas. I would simply supply the data to the component and React would re-render the changes.

I have marked of in the return statement where I believe the correct code should go.

The HTML code:

<div id='wrapper'>
    <canvas id='canvas'></canvas>
</div>

The jsx code:

var MyCanvas = React.createClass({
    render:function(){
        var line = this.props.lines;
        var ctx = this.props.canvas.getContext("2d");

        ctx.strokeStyle = 'rgba(0,0,0,0.5)';
        ctx.beginPath();
        ctx.moveTo(line[0].x0, line[0].y0);
        // .... more code .....
        ctx.stroke();

        return(
            <div>
                /* *********************************
                ??? RETURN MY RENDERED CANVAS
                    WITH GRAPHIC LINES. ????
             This is where I want to return the canvas 
                *********************************  */
            </div>
        );

    }
});


var wrapper = document.getElementById('wrapper');
var canvas = document.getElementById('canvas');
var line1 = { x0: 0, y0: 10, x1: 20, y1: 30 };
var line2 = { x0: 40, y0: 50, x1: 60, y1: 70 };

var myCanvas = <MyCanvas canvas={ canvas } lines={ [line1, line2] } />;
React.render(myCanvas, wrapper);

Hope I made myself clear.

Your only error was that you were not familar with react refs. try this:

class ConnectionChart extends React.Component {

    componentDidMount() {
        let canvas = ReactDOM.findDOMNode(this.refs.myCanvas);
        let ctx = canvas.getContext('2d');

        ctx.fillStyle = 'rgb(200,0,0)';
        ctx.fillRect(10, 10, 55, 50);
    }

    render() {
        return (
            <div>
                <canvas ref="myCanvas" />
            </div>
        );
    }
}

You might have get rid of the ES6 style but you get the idea. Of cause u can paint in other methods too ^^

I am trying to render a canvas using React. The graphics inside the canvas would also be handled by Reacts render method. The current code does render a  javascript - game - Rendering/Returning HTML5 Canvas in ReactJS . rendering graphics with react (2) I am trying to render a canvas using React. The graphics inside the canvas would also be handled by Reacts

Instead of using the canvas in your render method, you'd do something like this:

var MyCanvas = React.createClass({
  componentDidMount: function () {
    React.getDOMNode(this).appendChild(this.props.canvas);
  },
  render: function() {
    return <div />;
  }
});

You just render an empty div and wait for React to mount that. When mounted, you append your canvas to the actual DOM node that React created.

The reason for this is that the render method only returns virtual DOM nodes that React then translates to real DOM nodes. And since you have a real DOM node, you can't convert that to a virtual node. Another reason for is that you should only return nodes from render that React controls. And since you're managing the canvas from outside of Reacts control, you should use real DOM apis do manage it.

First we need our <canvas> and <img> elements. class Canvas extends React.​Component {render() { return( <div> <canvas ref="canvas"  I am trying to set up a canvas render system for some React components (they also can render in SVG, depending on their properties). I haven't settled on how best to do this, but the approach I'm currently taking is to have a CanvasManager component, combined with canvasContents methods on the child components that take a context and draw their intended contents.

The key is overriding the right React lifecycle methods to do the drawing. The render method creates the canvas DOM element and you can add a refs callback to set a reference to it, but you have to wait until the component is mounted to draw on the canvas.

Here's an example that uses a callback ref as the React docs recommend. It is designed to render a static (non-animated) graphic component based on props and updates when props change. It also subscribes to the window resize event so that it can be dynamically sized via CSS (such as width: 100%). This example is based on the code from this Gist.

export default class CanvasComponent extends React.Component {

    constructor(props) {
        super(props);

        this._resizeHandler = () => {
            /* Allows CSS to determine size of canvas */
            this.canvas.width = this.canvas.clientWidth;
            this.canvas.height = this.canvas.clientHeight;

            this.clearAndDraw();
        }
    }

    componentDidMount() {
        window.addEventListener('resize', this._resizeHandler);

        /* Allows CSS to determine size of canvas */
        this.canvas.width = this.canvas.clientWidth;
        this.canvas.height = this.canvas.clientHeight;

        this.clearAndDraw();
    }

    componentWillUnmount() {
        window.removeEventListener('resize', this._resizeHandler);
    }

    componentDidUpdate(prevProps, prevState) {
        if (this.props.secondRect !== prevProps.secondRect) {
            this.clearAndDraw();
        }
    }

    clearAndDraw() {
        const ctx = this.canvas.getContext('2d');
        if (ctx) {
            ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);
            this.draw(ctx);
        }
    }

    draw(ctx) {
        ctx.fillStyle = 'rgb(200, 0, 0)';
        ctx.fillRect(10, 10, 50, 50);

        if (this.props.secondRect) {
            ctx.fillStyle = 'rgba(0, 0, 200, 0.5)';
            ctx.fillRect(30, 30, 50, 50);
        }
    }

    render() {
        return (
            <canvas ref={canvas => this.canvas = canvas} />
        );
    }
}

You can set the secondRect prop from the parent component or set it from state to see the component update when the prop updates. You can extend this idea to build any kind of data-driven canvas rendering, such as a chart or graph.

fillRect(0,0, 100, 100); } render() { return ( <canvas ref="canvas" width={300} Thanks https://github.com/reactjs/react-art for providing good  dangerouslySetInnerHTML should not be used unless absolutely necessary. According to the docs, "This is mainly for cooperating with DOM string manipulation libraries".When you use it, your giving up the benefit of React's DOM management.

I thought I would update this answer using the React.createRef() because the this.refs is now legacy. Refs and the DOM

import React from "react";
import * as PropTypes from "prop-types";

class Canvas extends React.Component {
    constructor() {
        super()
        this.canvas = React.createRef()
    }
    componentDidMount() {
        const ctx = this.canvas.current.getContext('2d')
        this.props.draw(ctx);
    }
    render() {
        return <canvas ref={this.canvas} />;        
    }
}
Canvas.propTypes = {
  draw: PropTypes.func.isRequired
};
export default Canvas

You would use this Canvas by supplying the draw context.

<Canvas  
  draw={ctx => {
    ctx.beginPath();
    ctx.arc(95, 50, 40, 0, 2 * Math.PI);
    ctx.closePath();
    ctx.stroke();
    }
  }
/>

If you've worked with an HTML5 <canvas> before, you'll also know that to get a context with createRef(); } render() { return ( <div> <canvas ref={this. A lot of building with React is about maintaining the state of the view. Re-rendering the entire tree shouldn't cause your canvas to flicker. But if you think that re-rendering is causing this issue, you could use shouldComponentUpdate lifecycle function and return false whenever you don't want to to update.

In this tutorial I will use React Hooks to create an html canvas drawing website. I will start from zero return ( <canvas ref={canvasRef} width={window.innerWidth​} In the current implementation every render first clears the canvas and then draws all the locations. JavaScript · React · Reactjs · React Hook  Using React with canvas element. Anton Lavrenov . Follow. Feb 1, 2016 · 4 min read. We have React that helps us to work with massive mutable DOM in a nice immutable functional style. That is

If you've worked with an HTML5 <canvas> before, you'll also know that to When you come to render the canvas element, add a prop called ref that A lot of building with React is about maintaining the state of the view. provided through the props to return the canvas context to the parent component. Techniques for Animating on the Canvas in React If you've worked with an HTML5 <canvas> before, you'll also know that to get a context with which to draw on the canvas, you need to call

The HTML5 canvas element behaves differently than standard HTML elements, especially when embedded in a React.js application. In this guide, we will take a look at how to set up a basic React.js… The application will render the canvas element, and will draw a heart at Back to the App.js return():. react-canvas. Introductory blog post. React Canvas adds the ability for React components to render to <canvas> rather than DOM.. This project is a work-in-progress. Though much of the code is in production on flipboard.com, the React canvas bindings are relatively new and the API is subject to change.

Comments
  • A note from React docs: "Although string refs are not deprecated, they are considered legacy, and will likely be deprecated at some point in the future. Callback refs are preferred."
  • Good answer but they are considered legacy now see -> facebook.github.io/react/docs/…
  • First question: Does it matter if I call my graphics drawing routines in componentDidMount or render?
  • Second question: Would managing the canvas from within React (its creation and referencing) be more to Reacts way of doing things? My idea is to make this component part of a larger set of React components.
  • First question: Yes, it matters. render can be called any number of times during the lifetime of the component instance, whereas componentDidMount will only be called once. Be sure to implement componentWillUnmount as well and do cleanup there.
  • Second question: Depends on what you want to do with the canvas. The problem is that the canvas API is imperitive and not declarative, so you'd need something like this to do it: github.com/Flipboard/react-canvas
  • Note that React.getDOMNode() is deprecated: facebook.github.io/react/docs/component-api.html
  • I edited the example to also show the best practice of checking if relevant props or state changed in componentDidUpdate before redrawing the canvas. If you don't check that the props or state actually changed, you may end up redrawing the canvas much more frequently than necessary.