React Canvas App

This is a demo and starter template for an interactive canvas based animation. I use it in personal projects for experimenting in generative art and physics simulations.

Quick start

• Pull done a copy with degit: npx degit https://github.com/luke-codewalker/react-canvas-app#main <your-project-name>.
• Install all dependencies with npm i
• Run it in development mode with npm start

Customize

To customize the app there are two places to edit, depending on what you want to do:

Animation in src/art/draw.ts

This file contains the code for setting up and running your animation frame by frame. It is essentially a factory function that receives the canvas, the drawing context and any custom external dependencies you speficy.

import { Animation } from "../lib/canvas";
const size = 20;

export const draw: Animation<[number]> = (canvas: HTMLCanvasElement, context: CanvasRenderingContext2D, [stepSize]) => {
    // this code is run before the animation whenever the external dependencies change or the animation is reset
    let x = 0;
    const y = canvas.height / 2;
    context.fillStyle = '#333';

    // this function is called to paint each frame of the animation
    return ({ frameCount, stopAnimation, startAnimation, resetAnimation }) => {
        // this is a closure so we can access anything from setup
        context.clearRect(0, 0, canvas.width, canvas.height);
        context.fillRect(x, y, size, size);
        x = (x + stepSize) % canvas.width;

        if (frameCount === 314) {
            // you can stop an (re)start the animation any time you like
            stopAnimation();
            setTimeout(startAnimation, 1000)
        };

        if (frameCount === canvas.width) {
            // if you want to start over use resetAnimation(), this will call your draw function again
            // and start a new animation loop
            resetAnimation();
        }
    }
}

It is run once and the function you return from it is run on every animation cycle to paint a new frame to the canvas. Thanks to the magic of React hooks the factory is run again automatically if any of the dependencies change (that's also how resetAnimation() works).

Async animation

The function to paint each frame can return a promise so you can also do asynchronous operations that will be awaited between renders:

import { Animation } from "../lib/canvas";

export const draw: Animation<[number]> = (canvas: HTMLCanvasElement, context: CanvasRenderingContext2D, [stepSize]) => {
    return async () => {
        const res = await fetch('https://random-data-api.com/api/color/random_color');
        const data = await res.json();
        context.fillStyle = data.hex_value;
        context.fillRect(0, 0, canvas.width, canvas.height);
        await new Promise<void>((resolve) => {
            setTimeout(() => resolve(), 5000);
        })
    }
}

Interactivity in src/app/App.ts

This is the place where the stateful logic lives (which you can pass as dependencies into the animation). If you want to change any of the controls or add event listeners this is the place to do it.

It's a React app, so you can do anything here you can do in React.