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/**
* The main idea and some parts of the code (e.g. drawing variable width Bézier curve) are taken from:
* http://corner.squareup.com/2012/07/smoother-signatures.html
*
* Implementation of interpolation using cubic Bézier curves is taken from:
* http://www.benknowscode.com/2012/09/path-interpolation-using-cubic-bezier_9742.html
*
* Algorithm for approximated length of a Bézier curve is taken from:
* http://www.lemoda.net/maths/bezier-length/index.html
*/
import { Bezier } from './bezier';
import { BasicPoint, Point } from './point';
import { throttle } from './throttle';
declare global {
interface CSSStyleDeclaration {
msTouchAction: string;
}
}
export interface Options {
dotSize?: number | (() => number);
minWidth?: number;
maxWidth?: number;
minDistance?: number;
backgroundColor?: string;
penColor?: string;
throttle?: number;
velocityFilterWeight?: number;
onBegin?: (event: MouseEvent | Touch) => void;
onEnd?: (event: MouseEvent | Touch) => void;
}
export interface PointGroup {
color: string;
points: BasicPoint[];
}
export default class SignaturePad {
// Public stuff
public dotSize: number | (() => number);
public minWidth: number;
public maxWidth: number;
public minDistance: number;
public backgroundColor: string;
public penColor: string;
public throttle: number;
public velocityFilterWeight: number;
public onBegin?: (event: MouseEvent | Touch) => void;
public onEnd?: (event: MouseEvent | Touch) => void;
// Private stuff
/* tslint:disable: variable-name */
private _ctx: CanvasRenderingContext2D;
private _mouseButtonDown: boolean;
private _isEmpty: boolean;
private _lastPoints: Point[]; // Stores up to 4 most recent points; used to generate a new curve
private _data: PointGroup[]; // Stores all points in groups (one group per line or dot)
private _lastVelocity: number;
private _lastWidth: number;
private _strokeMoveUpdate: (event: MouseEvent | Touch) => void;
/* tslint:enable: variable-name */
constructor(
private canvas: HTMLCanvasElement,
private options: Options = {},
) {
this.velocityFilterWeight = options.velocityFilterWeight || 0.7;
this.minWidth = options.minWidth || 0.5;
this.maxWidth = options.maxWidth || 2.5;
this.throttle = ('throttle' in options ? options.throttle : 16) as number; // in milisecondss
this.minDistance = ('minDistance' in options
? options.minDistance
: 5) as number; // in pixels
this.dotSize =
options.dotSize ||
function dotSize(this: SignaturePad): number {
return (this.minWidth + this.maxWidth) / 2;
};
this.penColor = options.penColor || 'black';
this.backgroundColor = options.backgroundColor || 'rgba(0,0,0,0)';
this.onBegin = options.onBegin;
this.onEnd = options.onEnd;
this._strokeMoveUpdate = this.throttle
? throttle(SignaturePad.prototype._strokeUpdate, this.throttle)
: SignaturePad.prototype._strokeUpdate;
this._ctx = canvas.getContext('2d') as CanvasRenderingContext2D;
this.clear();
// Enable mouse and touch event handlers
this.on();
}
public clear(): void {
const { _ctx: ctx, canvas } = this;
// Clear canvas using background color
ctx.fillStyle = this.backgroundColor;
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.fillRect(0, 0, canvas.width, canvas.height);
this._data = [];
this._reset();
this._isEmpty = true;
}
public fromDataURL(
dataUrl: string,
options: { ratio?: number; width?: number; height?: number } = {},
callback?: (error?: string | Event) => void,
): void {
const image = new Image();
const ratio = options.ratio || window.devicePixelRatio || 1;
const width = options.width || this.canvas.width / ratio;
const height = options.height || this.canvas.height / ratio;
this._reset();
image.onload = (): void => {
this._ctx.drawImage(image, 0, 0, width, height);
if (callback) {
callback();
}
};
image.onerror = (error): void => {
if (callback) {
callback(error);
}
};
image.src = dataUrl;
this._isEmpty = false;
}
public toDataURL(type = 'image/png', encoderOptions?: number): string {
switch (type) {
case 'image/svg+xml':
return this._toSVG();
default:
return this.canvas.toDataURL(type, encoderOptions);
}
}
public on(): void {
// Disable panning/zooming when touching canvas element
this.canvas.style.touchAction = 'none';
this.canvas.style.msTouchAction = 'none';
if (window.PointerEvent) {
this._handlePointerEvents();
} else {
this._handleMouseEvents();
if ('ontouchstart' in window) {
this._handleTouchEvents();
}
}
}
public off(): void {
// Enable panning/zooming when touching canvas element
this.canvas.style.touchAction = 'auto';
this.canvas.style.msTouchAction = 'auto';
this.canvas.removeEventListener('pointerdown', this._handleMouseDown);
this.canvas.removeEventListener('pointermove', this._handleMouseMove);
document.removeEventListener('pointerup', this._handleMouseUp);
this.canvas.removeEventListener('mousedown', this._handleMouseDown);
this.canvas.removeEventListener('mousemove', this._handleMouseMove);
document.removeEventListener('mouseup', this._handleMouseUp);
this.canvas.removeEventListener('touchstart', this._handleTouchStart);
this.canvas.removeEventListener('touchmove', this._handleTouchMove);
this.canvas.removeEventListener('touchend', this._handleTouchEnd);
}
public isEmpty(): boolean {
return this._isEmpty;
}
public fromData(pointGroups: PointGroup[]): void {
this.clear();
this._fromData(
pointGroups,
({ color, curve }) => this._drawCurve({ color, curve }),
({ color, point }) => this._drawDot({ color, point }),
);
this._data = pointGroups;
}
public toData(): PointGroup[] {
return this._data;
}
// Event handlers
private _handleMouseDown = (event: MouseEvent): void => {
if (event.which === 1) {
this._mouseButtonDown = true;
this._strokeBegin(event);
}
};
private _handleMouseMove = (event: MouseEvent): void => {
if (this._mouseButtonDown) {
this._strokeMoveUpdate(event);
}
};
private _handleMouseUp = (event: MouseEvent): void => {
if (event.which === 1 && this._mouseButtonDown) {
this._mouseButtonDown = false;
this._strokeEnd(event);
}
};
private _handleTouchStart = (event: TouchEvent): void => {
// Prevent scrolling.
event.preventDefault();
if (event.targetTouches.length === 1) {
const touch = event.changedTouches[0];
this._strokeBegin(touch);
}
};
private _handleTouchMove = (event: TouchEvent): void => {
// Prevent scrolling.
event.preventDefault();
const touch = event.targetTouches[0];
this._strokeMoveUpdate(touch);
};
private _handleTouchEnd = (event: TouchEvent): void => {
const wasCanvasTouched = event.target === this.canvas;
if (wasCanvasTouched) {
event.preventDefault();
const touch = event.changedTouches[0];
this._strokeEnd(touch);
}
};
// Private methods
private _strokeBegin(event: MouseEvent | Touch): void {
const newPointGroup = {
color: this.penColor,
points: [],
};
if (typeof this.onBegin === 'function') {
this.onBegin(event);
}
this._data.push(newPointGroup);
this._reset();
this._strokeUpdate(event);
}
private _strokeUpdate(event: MouseEvent | Touch): void {
if (this._data.length === 0) {
// This can happen if clear() was called while a signature is still in progress,
// or if there is a race condition between start/update events.
this._strokeBegin(event);
return;
}
const x = event.clientX;
const y = event.clientY;
const point = this._createPoint(x, y);
const lastPointGroup = this._data[this._data.length - 1];
const lastPoints = lastPointGroup.points;
const lastPoint =
lastPoints.length > 0 && lastPoints[lastPoints.length - 1];
const isLastPointTooClose = lastPoint
? point.distanceTo(lastPoint) <= this.minDistance
: false;
const color = lastPointGroup.color;
// Skip this point if it's too close to the previous one
if (!lastPoint || !(lastPoint && isLastPointTooClose)) {
const curve = this._addPoint(point);
if (!lastPoint) {
this._drawDot({ color, point });
} else if (curve) {
this._drawCurve({ color, curve });
}
lastPoints.push({
time: point.time,
x: point.x,
y: point.y,
});
}
}
private _strokeEnd(event: MouseEvent | Touch): void {
this._strokeUpdate(event);
if (typeof this.onEnd === 'function') {
this.onEnd(event);
}
}
private _handlePointerEvents(): void {
this._mouseButtonDown = false;
this.canvas.addEventListener('pointerdown', this._handleMouseDown);
this.canvas.addEventListener('pointermove', this._handleMouseMove);
document.addEventListener('pointerup', this._handleMouseUp);
}
private _handleMouseEvents(): void {
this._mouseButtonDown = false;
this.canvas.addEventListener('mousedown', this._handleMouseDown);
this.canvas.addEventListener('mousemove', this._handleMouseMove);
document.addEventListener('mouseup', this._handleMouseUp);
}
private _handleTouchEvents(): void {
this.canvas.addEventListener('touchstart', this._handleTouchStart);
this.canvas.addEventListener('touchmove', this._handleTouchMove);
this.canvas.addEventListener('touchend', this._handleTouchEnd);
}
// Called when a new line is started
private _reset(): void {
this._lastPoints = [];
this._lastVelocity = 0;
this._lastWidth = (this.minWidth + this.maxWidth) / 2;
this._ctx.fillStyle = this.penColor;
}
private _createPoint(x: number, y: number): Point {
const rect = this.canvas.getBoundingClientRect();
return new Point(x - rect.left, y - rect.top, new Date().getTime());
}
// Add point to _lastPoints array and generate a new curve if there are enough points (i.e. 3)
private _addPoint(point: Point): Bezier | null {
const { _lastPoints } = this;
_lastPoints.push(point);
if (_lastPoints.length > 2) {
// To reduce the initial lag make it work with 3 points
// by copying the first point to the beginning.
if (_lastPoints.length === 3) {
_lastPoints.unshift(_lastPoints[0]);
}
// _points array will always have 4 points here.
const widths = this._calculateCurveWidths(_lastPoints[1], _lastPoints[2]);
const curve = Bezier.fromPoints(_lastPoints, widths);
// Remove the first element from the list, so that there are no more than 4 points at any time.
_lastPoints.shift();
return curve;
}
return null;
}
private _calculateCurveWidths(
startPoint: Point,
endPoint: Point,
): { start: number; end: number } {
const velocity =
this.velocityFilterWeight * endPoint.velocityFrom(startPoint) +
(1 - this.velocityFilterWeight) * this._lastVelocity;
const newWidth = this._strokeWidth(velocity);
const widths = {
end: newWidth,
start: this._lastWidth,
};
this._lastVelocity = velocity;
this._lastWidth = newWidth;
return widths;
}
private _strokeWidth(velocity: number): number {
return Math.max(this.maxWidth / (velocity + 1), this.minWidth);
}
private _drawCurveSegment(x: number, y: number, width: number): void {
const ctx = this._ctx;
ctx.moveTo(x, y);
ctx.arc(x, y, width, 0, 2 * Math.PI, false);
this._isEmpty = false;
}
private _drawCurve({ color, curve }: { color: string; curve: Bezier }): void {
const ctx = this._ctx;
const widthDelta = curve.endWidth - curve.startWidth;
// '2' is just an arbitrary number here. If only lenght is used, then
// there are gaps between curve segments :/
const drawSteps = Math.floor(curve.length()) * 2;
ctx.beginPath();
ctx.fillStyle = color;
for (let i = 0; i < drawSteps; i += 1) {
// Calculate the Bezier (x, y) coordinate for this step.
const t = i / drawSteps;
const tt = t * t;
const ttt = tt * t;
const u = 1 - t;
const uu = u * u;
const uuu = uu * u;
let x = uuu * curve.startPoint.x;
x += 3 * uu * t * curve.control1.x;
x += 3 * u * tt * curve.control2.x;
x += ttt * curve.endPoint.x;
let y = uuu * curve.startPoint.y;
y += 3 * uu * t * curve.control1.y;
y += 3 * u * tt * curve.control2.y;
y += ttt * curve.endPoint.y;
const width = Math.min(
curve.startWidth + ttt * widthDelta,
this.maxWidth,
);
this._drawCurveSegment(x, y, width);
}
ctx.closePath();
ctx.fill();
}
private _drawDot({
color,
point,
}: {
color: string;
point: BasicPoint;
}): void {
const ctx = this._ctx;
const width =
typeof this.dotSize === 'function' ? this.dotSize() : this.dotSize;
ctx.beginPath();
this._drawCurveSegment(point.x, point.y, width);
ctx.closePath();
ctx.fillStyle = color;
ctx.fill();
}
private _fromData(
pointGroups: PointGroup[],
drawCurve: SignaturePad['_drawCurve'],
drawDot: SignaturePad['_drawDot'],
): void {
for (const group of pointGroups) {
const { color, points } = group;
if (points.length > 1) {
for (let j = 0; j < points.length; j += 1) {
const basicPoint = points[j];
const point = new Point(basicPoint.x, basicPoint.y, basicPoint.time);
// All points in the group have the same color, so it's enough to set
// penColor just at the beginning.
this.penColor = color;
if (j === 0) {
this._reset();
}
const curve = this._addPoint(point);
if (curve) {
drawCurve({ color, curve });
}
}
} else {
this._reset();
drawDot({
color,
point: points[0],
});
}
}
}
private _toSVG(): string {
const pointGroups = this._data;
const ratio = Math.max(window.devicePixelRatio || 1, 1);
const minX = 0;
const minY = 0;
const maxX = this.canvas.width / ratio;
const maxY = this.canvas.height / ratio;
const svg = document.createElementNS('http://www.w3.org/2000/svg', 'svg');
svg.setAttribute('width', this.canvas.width.toString());
svg.setAttribute('height', this.canvas.height.toString());
this._fromData(
pointGroups,
({ color, curve }: { color: string; curve: Bezier }) => {
const path = document.createElement('path');
// Need to check curve for NaN values, these pop up when drawing
// lines on the canvas that are not continuous. E.g. Sharp corners
// or stopping mid-stroke and than continuing without lifting mouse.
/* eslint-disable no-restricted-globals */
if (
!isNaN(curve.control1.x) &&
!isNaN(curve.control1.y) &&
!isNaN(curve.control2.x) &&
!isNaN(curve.control2.y)
) {
const attr =
`M ${curve.startPoint.x.toFixed(3)},${curve.startPoint.y.toFixed(
3,
)} ` +
`C ${curve.control1.x.toFixed(3)},${curve.control1.y.toFixed(3)} ` +
`${curve.control2.x.toFixed(3)},${curve.control2.y.toFixed(3)} ` +
`${curve.endPoint.x.toFixed(3)},${curve.endPoint.y.toFixed(3)}`;
path.setAttribute('d', attr);
path.setAttribute('stroke-width', (curve.endWidth * 2.25).toFixed(3));
path.setAttribute('stroke', color);
path.setAttribute('fill', 'none');
path.setAttribute('stroke-linecap', 'round');
svg.appendChild(path);
}
/* eslint-enable no-restricted-globals */
},
({ color, point }: { color: string; point: BasicPoint }) => {
const circle = document.createElement('circle');
const dotSize =
typeof this.dotSize === 'function' ? this.dotSize() : this.dotSize;
circle.setAttribute('r', dotSize.toString());
circle.setAttribute('cx', point.x.toString());
circle.setAttribute('cy', point.y.toString());
circle.setAttribute('fill', color);
svg.appendChild(circle);
},
);
const prefix = 'data:image/svg+xml;base64,';
const header =
'<svg' +
' xmlns="http://www.w3.org/2000/svg"' +
' xmlns:xlink="http://www.w3.org/1999/xlink"' +
` viewBox="${minX} ${minY} ${maxX} ${maxY}"` +
` width="${maxX}"` +
` height="${maxY}"` +
'>';
let body = svg.innerHTML;
// IE hack for missing innerHTML property on SVGElement
if (body === undefined) {
const dummy = document.createElement('dummy');
const nodes = svg.childNodes;
dummy.innerHTML = '';
// tslint:disable-next-line: prefer-for-of
for (let i = 0; i < nodes.length; i += 1) {
dummy.appendChild(nodes[i].cloneNode(true));
}
body = dummy.innerHTML;
}
const footer = '</svg>';
const data = header + body + footer;
return prefix + btoa(data);
}
}