A small JS library for beautiful drawing and handwriting on the HTML Canvas
This is a fork of jakubfiala/atrament.
Atrament is a library for drawing and hand writing on the HTML canvas. Its goal is for drawing to feel natural and comfortable, and the result to be smooth and pleasing. Atrament does not store the stroke paths itself - instead, it draws directly onto the canvas bitmap, just like an ink pen onto a piece of paper ("atrament" means ink in Slovak and Polish). This makes it suitable for certain applications, and not quite ideal for others — see Alternatives.
Features:
- Draw/Fill/Erase modes
- Adjustable adaptive smoothing
- Events tracking the drawing - this allows the app to "replay" or reconstruct the drawing, e.g. for undo functionality
- Adjustable line thickness and colour
Enjoy!
npm i -S @substrate-system/atrament<canvas id="sketchpad" width="500" height="500"></canvas>In your JavaScript, create an Atrament instance passing it your canvas object:
import Atrament from 'atrament';
const canvas = document.querySelector('#sketchpad');
const sketchpad = new Atrament(canvas);You can also pass the width, height and default colour to the constructor (see note on high DPI screens)
const sketchpad = new Atrament(canvas, {
width: 500,
height: 500,
color: 'orange',
});That's it, happy drawing!
sketchpad.clear();sketchpad.weight = 20; // in pixelssketchpad.color = '#ff485e'; // just like CSSNote
For Fill mode, you must also set the fillWorker config option in the
constructor. See next section
import { MODE_DRAW, MODE_ERASE, MODE_FILL, MODE_DISABLED } from 'atrament';
sketchpad.mode = MODE_DRAW; // default
sketchpad.mode = MODE_ERASE; // eraser tool
sketchpad.mode = MODE_FILL; // click to fill area (see next section for more info)
sketchpad.mode = MODE_DISABLED; // no modification (will still fire stroke events)Tweak smoothing - higher values make the drawings look smoother, lower values
make drawing feel a bit more responsive. Set to 0.85 by default.
sketchpad.smoothing = 1.3;Toggle adaptive stroke, i.e. line width changing based on drawing speed and
stroke progress. This simulates the variation in ink discharge of a physical
pen. true by default.
sketchpad.adaptiveStroke = false;Set pressure sensitivity. Note: if your input device sends pressure data, adaptive stroke will have no effect, since its purpose is to emulate changing pen pressure
// the lower bound of the pressure scale:
// at pressure = 0 the stroke width will be multiplied by 0
sketchpad.pressureLow = 0;
// the lower bound of the pressure scale:
// at pressure = 1 the stroke width will be multiplied by 2
sketchpad.pressureHigh = 2;
// at pressure = 0.5 the stroke width remains the same
// Amount of low-pass filtering applied to the pressure values.
// more smoothing might help remove artifacts at the end of strokes
// where the pressure-sensitive stylus has very low pressure.
// Range: 0-1 Default: 0.3
sketchpad.pressureSmoothing = 0.4;The secondaryMouseButton option enables drawing using the secondary (right)
mouse button - e.g. as a quick eraser. This is false by default.
sketchpad.secondaryMouseButton = true;Ignore strokes with modifier keys pressed (e.g. Alt/Ctrl/Cmd/Windows key).
false by default.
sketchpad.ignoreModifiers = true;Record stroke data (enables the strokerecorded event). false by default.
sketchpad.recordStrokes = true;From version 5.0.0, Atrament will not bundle the fill Worker within the main bundle. This is so applications that don't require fill mode benefit from about a 60% smaller import size. The fill module can be imported separately and injected into Atrament via the constructor.
If you're using Vite, you can use the ?worker import
syntax to inline the worker:
import Atrament from '@substrate-system/atrament';
import FillWorker from '@substrate-system/atrament/fill?worker';
const sketchpad = new Atrament(canvas, {
fill: new FillWorker()
});For non-Vite environments or pre-bundled browser builds, create the worker manually using the worker file URL:
import Atrament from '@substrate-system/atrament';
const fillWorker = new Worker(
new URL('@substrate-system/atrament/fill', import.meta.url),
{ type: 'module' }
);
const sketchpad = new Atrament(canvas, {
fill: fillWorker
});For direct browser usage with the minified bundle:
<script type="module">
import Atrament from './node_modules/@substrate-system/atrament/dist/index.min.js';
const fillWorker = new Worker(
'./node_modules/@substrate-system/atrament/dist/fill/worker.min.js',
{ type: 'module' }
);
const sketchpad = new Atrament(canvas, {
fill: fillWorker
});
</script>- Atrament models its output as a set of independent strokes. Only one stroke can be drawn at a time.
- Each stroke consists of a list of segments, which correspond to all the pointer positions recorded during drawing.
- Each segment consists of a point which contains
xandycoordinates, atimewhich is the number of milliseconds since the stroke began, until the segment was drawn, and apressurevalue (0.-1.) which is either the recorded stylus pressure or 0.5 if no pressure data is available. - Each stroke also contains information about the drawing settings at the time of drawing (see Events > Stroke recording).
These events fire when the canvas is first drawn on, and when it's cleared.
The state is stored in the dirty property.
sketchpad.addEventListener('dirty', () => console.info(sketchpad.dirty));
sketchpad.addEventListener('clean', () => console.info(sketchpad.dirty));These events inform that a stroke has started/finished. They also return
x and y properties denoting where on the canvas the event occurred.
sketchpad.addEventListener('strokestart', () => console.info('strokestart'));
sketchpad.addEventListener('strokeend', () => console.info('strokeend'));These only fire in fill mode. The fillstart event also contains
x and y properties denoting the starting point of the fill operation
(where the user has clicked).
sketchpad.addEventListener('fillstart', ({ x, y }) =>
console.info(`fillstart ${x} ${y}`),
);
sketchpad.addEventListener('fillend', () => console.info('fillend'));Sometimes you might want to tweak Atrament's settings as soon as the user
begins/ends a stroke, but before Atrament actually draws anything.
The pointerdown/up events allow you to do this. The argument is
the PointerEvent itself.
sketchpad.addEventListener('pointerdown', (event) => {
console.info('pointerdown', event);
})
sketchpad.addEventListener('pointerup', (event) => console.info('pointerup', event));The following events only fire if the recordStrokes property is set to true.
strokerecorded fires at the same time as strokeend and contains data
necessary for reconstructing the stroke.
segmentdrawn fires during stroke recording every time the draw method is
called. It contains the same data as strokerecorded.
sketchpad.addEventListener('strokerecorded', ({ stroke }) => {
console.info(stroke),
});
/*
{
segments: [
{
point: { x, y },
time,
pressure,
}
],
color,
weight,
smoothing,
adaptiveStroke,
}
*/
sketchpad.addEventListener('segmentdrawn', ({ stroke }) => {
console.info(stroke),
});To enable functionality such as undo/redo, stroke post-processing, and SVG export in apps using Atrament, the library can be configured to record and programmatically draw the strokes.
The first step is to enable recordStrokes, and add a listener for
the strokerecorded event:
atrament.recordStrokes = true;
atrament.addEventListener('strokerecorded', ({ stroke }) => {
// store `stroke` somewhere
});The stroke can then be reconstructed using methods of the Atrament class:
// set drawing options
atrament.mode = stroke.mode;
atrament.weight = stroke.weight;
atrament.smoothing = stroke.smoothing;
atrament.color = stroke.color;
atrament.adaptiveStroke = stroke.adaptiveStroke;
// don't want to modify original data
const segments = stroke.segments.slice();
const firstPoint = segments.shift().point;
// beginStroke moves the "pen" to the given position and starts the path
atrament.beginStroke(firstPoint.x, firstPoint.y);
let prevPoint = firstPoint;
while (segments.length > 0) {
const segment = segments.shift();
// the `draw` method accepts the current real coordinates
// (i. e. actual cursor position), and the previous processed (filtered)
// position. It returns an object with the current processed position.
const { x, y } = atrament.draw(
segment.point.x,
segment.point.y,
prevPoint.x,
prevPoint.y,
segment.pressure
);
// the processed position is the one where the line is actually drawn to
// so we have to store it and pass it to `draw` in the next step
prevPoint = { x, y };
}
// endStroke closes the path
atrament.endStroke(prevPoint.x, prevPoint.y);Atrament does not provide its own undo/redo functionality to keep the scope as small as possible. However, using stroke recording and programmatic drawing, it is possible to implement undo/redo with a relatively small amount of code. See @nidoro and @feored's example here.
The demo app is useful for development. It's a plain HTML website which can be served with any local server.
npm startAtrament's philosophy is to provide a simple and small tool that takes care of everything from pointer events to drawing pixels on screen. Atrament uses the native Canvas API to draw strokes, instead of computing custom curves. This means it's very lightweight (5.9kB gzipped with fill mode, 2.4kB without) and pretty much as fast as the browser allows.
This does mean Atrament's rendering quality is limited by the Canvas API.
If your application requires higher drawing quality, there are libraries such as
perfect-freehand which
compute their own curves and achieve somewhat more pleasing, higher-fidelity
results. This comes at the expense of size (perfect-freehand is almost 2kB
gzipped to generate the curve shape, but you need to take care of rendering
it, handling pointer interactions, etc.).
For a more fully-featured solution including drawing shapes, graphs, text, built-in Undo/Redo and many other features, you might want to consider a larger tool such as excalidraw.