scrawl-canvas

Welcome to the Scrawl-canvas Library

Version: 8.14.0 - 1 September 2024

Scrawl-canvas website: scrawl-v8.rikweb.org.uk.

• learning materials: scrawl-v8.rikweb.org.uk/learn.
• documentation: scrawl-v8.rikweb.org.uk/documentation.
• tests/demos: scrawl-v8.rikweb.org.uk/demonstrations.

Scrawl-canvas on CodePen: codepen.io/collection/RzzMjw.

Scrawl-canvas on Discord: discord.com/channels/...

Do you want to contribute? Don't be afraid - reach out and let's see what website magic we can create together!

What?

Scrawl-canvas is a Javascript library for working with the HTML5 <canvas> element. The library:

• Defines a set of factory functions for creating a wide range of graphic artefacts and effects, which can be drawn on a canvas.
• Includes an adaptable - yet easy to use - protocol for positioning, displaying and animating artefacts and effects across the canvas.
• Adds functionality to make <canvas> elements responsive, adapting their size to their surrounding environment while remaining fully interactive.
• Helps make canvas elements more accessible for both keyboard and AT users.

https://user-images.githubusercontent.com/5357530/141673995-df239c38-2ba1-43f3-831c-b655524f2f40.mp4

Why?

Working with the native Canvas API is hard work - particularly when the desired result is more complex than a couple of coloured boxes in a static display.

But the benefits of using canvases for graphical displays and animations are also great:

• Canvases are part of the DOM (unlike Flash);
• They are natively wired for events and user interactions;
• They use immediate mode redering (which makes them very quick); and
• The canvas-related APIs are designed to be used with Javascript.

Sadly these advantages are also significant barriers:

• Working directly with the canvas-related APIs means writing significant amounts of Javascript boilerplate code.
• <canvas> elements can be resized and styled using CSS, but changing the CSS size does not affect the element's drawing dimensions - leading to ugly results.
• Events work on the canvas, not on the graphical objects within the canvas - we cannot use those objects as links or hot-spots (click/tap events), we cannot give them the equivalent of a CSS hover state (focus/blur events), we cannot drag-and-drop them around the display (move events).
• Tracking a user's interaction with the various parts of a canvas display, for analytics and research on web page performance, is particularly difficult.
• We cannot easily save and share displays, effects and animations; each <canvas> element's output is tightly coupled to the code that defines that output.
• Of most concern, canvases are entirely graphical - visual - by nature; they come with significant accessibility issues. Given the ever-stricter requirements for websites to be accessible to all users, this makes using a canvas to present important information a dangerous proposition.

Scrawl-canvas overcomes these barriers

Scrawl-canvas is fast, and developer-friendly. It's suitable for building infographics, games, interactive videos - whatever we can imagine for a 2D graphical presentation. And it is modular - we can break the code for a particular effect into its own module file which can be reused in other projects.

Scrawl-canvas offers all of this while never losing its hard focus on making the <canvas> element accessible, responsive and fully interactive while at the same time offering a pleasant developer experience.

Also, Scrawl-canvas supports developers coding in TypeScript by means of a TS definitions file included in the repository.

Installation and use

There are three main ways to include Scrawl-canvas in your project:

Download, unpack, use

1. Download the zipped file from GitHub
2. Unzip the file to a folder in your project.
3. Import the library into the script code where you will be using it.

Alternatively, a zip package of the v8.14.0 files can be downloaded from this link: scrawl.rikweb.org.uk/downloads/scrawl-canvas_8-14-0.zip - that package only includes the minified file.

<!-- Hello world -->
<!DOCTYPE html>
<html>
<head>
    <title>Scrawl-canvas Hello World</title>
</head>
<body>
    
    <canvas id="my-canvas" data-scrawl-canvas></canvas>

    <!-- The library is entirely modular and needs to be imported into a module script -->
    <script type="module">

        import * as scrawl from './relative-or-absolute/path/to/scrawl-canvas/min/scrawl.js';

        // Get a handle to the canvas element
        let canvas = scrawl.findCanvas('my-canvas');

        // Setup the scene to be displayed in the canvas
        scrawl.makeLabel({

            name: 'hello',
            start: [20, 20],

            text: 'Hello, World!',
            fontString: 'bold 40px Garamond, serif',
        });

        // Render the canvas scene once
        canvas.render();

    </script>

</body>
</html>

CDN - unpkg.com

This will pull the requested npm package directly into your web page:

<script type="module">
    import * as scrawl from 'https://unpkg.com/scrawl-canvas@8.14.0';
    [...]
</script>

NPM/Yarn

1. Add the library to your project using NPM or Yarn
2. Import the library into the script code where you will be using it.

// either
$> npm install scrawl-canvas

// or
$> yarn add scrawl-canvas

// then in your script file
import * as scrawl from 'scrawl-canvas';

// Scrawl-canvas has no dependencies
// - it can be used as-is, with no further installation steps required

Local development and testing

After forking this repo down to your local machine, cd into the scrawl-canvas folder, run yarn install or npm install (for the local build toolchain - the library itself has no external dependencies) and start a local server.

$> cd ./path/to/Scrawl-canvas/folder
$> yarn install
$> yarn dev

Testing

The code base does not include any unit testing frameworks. Instead, we rely on a set of Demo tests which allow us to perform integration testing and user interface testing.

Why this approach? Because most of the Scrawl-canvas functionality revolves around various forms of user interaction and animation, which requires visual inspection of the Demo tests to check that the canvas display - and thus, by inference, the underlying code - performs as expected.

Demos that include user interaction allow us to test specific aspects of the code base.

Linting

The tool chain includes the ESLint package to impose some basic checks on code. We use the default checks supplied by the package (as indicated in the rules documentation page). To run the linter:

$> yarn lint

The tool chain also includes the Knip package to check for unused files and exports in the source Javascript. To run Knip:

$> yarn knip

TypeScript support

Scrawl-canvas supports TypeScript through a TypeScript Definitions (d.ts) file. The definitions file aims to be as accurate, comprehensive and informative as possible, but specifically excludes support for internal (private) SC object attributes and functions.

To view the library's API types, try the tsdocs.dev website.

To aid development, we test the definitions file against the entire suite of Demo code .js files supplied as part of the library. From the root of the project, run the following command:

$> yarn test

Documentation

The source code has been extensively commented. We generate documentation from that code using Docco. Documentation is regenerated each time the library is rebuilt.

Minification

We minify the source code using rollup and its terser plugin.

Building the library

Running the following command on the command line will recreate the minified file, and regenerate the documentation:

$> yarn build

Star History

Development team

Developed by Rik Roots: [e-mail]