目录
前言
一、HTML5 Canvas 简介
二、签字功能的实现
效果演示
完整代码
前言
在现代互联网应用中，有时我们需要让用户在网页上进行签字操作，比如确认文件、填写电子表格或者签署合同。利用 HTML5 的 canvas 画布，我们可以轻松地实现这一功能，为用户提供方便快捷的在线签字体验。
一、HTML5 Canvas 简介
HTML5 的 canvas 元素是一种强大的图形渲染工具，它允许开发者使用 JavaScript 在网页上绘制各种图形、动画和交互式内容。通过 canvas，开发者可以创建丰富多彩的视觉效果，并实现复杂的用户交互体验。
HTML5 Canvas的关键特性：
图形绘制能力：Canvas 元素提供了绘制路径、矩形、圆形、直线、文本等基本图形的功能，同时还支持图像的绘制和变换操作，使得开发者能够轻松地创建各种视觉效果。
动画和交互：借助 JavaScript，开发者可以在 Canvas 上创建复杂的动画效果，并添加交互式的操作。这使得 Canvas 成为开发游戏、数据可视化和其他需要动态效果的应用的理想选择。
性能优势：由于 Canvas 是基于 GPU 加速的，因此它具有良好的性能表现，能够处理大量的图形元素和动画效果，而不会对页面的整体性能产生太大影响。
灵活性：Canvas 元素可以轻松地与其他 HTML 元素结合使用，使得开发者可以在页面上创建复杂的混合媒体效果，同时还可以响应用户的交互操作。
二、签字功能的实现
效果演示
完整代码
HTML代码
<!DOCTYPE html>
<html class="no-js">
<head><meta name="viewport"content="width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0,user-scalable=no,viewport-fit=cover"><meta http-equiv="Cache-Control" content="no-cache, no-store, must-revalidate" /><meta http-equiv="expires" CONTENT="Wed, 26 Feb 1997 08:21:57 GMT"><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta http-equiv="Pragma" content="no-cache"><meta http-equiv="Cache" content="no-cache"><meta http-equiv="Expires" content="0"><meta charset="utf-8"><title>画图</title><link rel="stylesheet" href="css/bootstrap.css"><style>* {margin: 0;padding: 0;}html,body {width: 100%;height: 100%;text-align: center;}canvas {max-width: 100%;border: 2px dotted #ccc;}</style>
</head><body><script src="./index.js"></script><script>//初始化var sign = new Draw( {// canvas:document.getElementById('canvas'),lineWidth: 10, // 线条宽度width: 400, // canvas 宽height: 400, //canvas 高strokeStyle: '#333333' // 线条颜色} );window.onload = function () {// 点击输出图片document.querySelector( '.ouput' ).onclick = function () {var img = new Image();img.style.width = '200px';img.src = sign.ouput();img.onload = function () {document.body.appendChild( img );}document.querySelector( 'img' ) && document.querySelector( 'img' ).remove();}// 点击清除document.querySelector( '.clear' ).onclick = function () {sign.clear();}// 点击撤销document.querySelector( '.undo' ).onclick = function () {if ( sign.state.undopath.length > 0 ) {sign.undo();} else {console.log( '还没有签名' );}}}</script><div class="buttons"><button type="button" class="btn btn-primary ouput">生成图片</button><button type="button" class="btn btn-light undo">撤销</button><button type="button" class="btn btn-light clear">清除画布</button></div>
</body></html>js代码
( function ( global, factory ) {typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :typeof define === 'function' && define.amd ? define( factory ) :( global = global || self, global.Draw = factory() );
}( this, ( function () {'use strict';var classCallCheck = function ( instance, Constructor ) {if ( !( instance instanceof Constructor ) ) {throw new TypeError( "Cannot call a class as a function" );}};var createClass = function () {function defineProperties ( target, props ) {for ( var i = 0; i < props.length; i++ ) {var descriptor = props[i];descriptor.enumerable = descriptor.enumerable || false;descriptor.configurable = true;if ( "value" in descriptor ) descriptor.writable = true;Object.defineProperty( target, descriptor.key, descriptor );}}return function ( Constructor, protoProps, staticProps ) {if ( protoProps ) defineProperties( Constructor.prototype, protoProps );if ( staticProps ) defineProperties( Constructor, staticProps );return Constructor;};}();/*** * @description 手写签字版*/var Draw = function () {function Draw () {var params = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : {};classCallCheck( this, Draw );this.el = params.el || document.createElement( 'canvas' );this.state = {undopath: [],index: -1,old: void 0,isStart: false,width: params.width || 400,height: params.height || 400,lineWidth: params.lineWidth || 1,isTouch: 'ontouchstart' in window,strokeStyle: params.strokeStyle || '#333333'};var _state = this.state,width = _state.width,height = _state.height,lineWidth = _state.lineWidth;this.el.width = width * 2;this.el.height = height * 2;document.body.appendChild( this.el );this.ctx = this.el.getContext( '2d' );this.ctx.scale( 2, 2 );this.ctx.lineWidth = lineWidth;this.ctx.lineJoin = 'round';this.ctx.lineCap = 'round';this.init();}createClass( Draw, [{key: 'onStart',value: function onStart () {++this.state.index;this.state.isStart = true;}}, {key: 'onMove',value: function onMove ( e ) {e.preventDefault();if ( !this.state.isStart ) return;var pos = this.pos( e );var index = this.state.index;this.ctx.strokeStyle = this.state.strokeStyle;if ( this.state.old ) {this.ctx.beginPath();this.ctx.moveTo( this.state.old.x, this.state.old.y );this.ctx.lineTo( pos.x, pos.y );this.ctx.stroke();}this.state.old = pos;if ( this.state.undopath[index] ) {this.state.undopath[index].push( { x: this.state.old.x, y: this.state.old.y } );} else {this.state.undopath[index] = [{x: this.state.old.x,y: this.state.old.y,strokeStyle: this.ctx.strokeStyle,lineWidth: this.ctx.lineWidth}];}}}, {key: 'onEnd',value: function onEnd () {this.state.old = void 0;this.state.isStart = false;}}, {key: 'pos',value: function pos ( e ) {var x = 0,y = 0;if ( e.touches ) {x = e.touches[0].pageX;y = e.touches[0].pageY;} else {x = e.offsetX / 2;y = e.offsetY / 2;}return { x: x, y: y };}}, {key: 'ouput',value: function ouput () {// 输出图片return this.el.toDataURL();}}, {key: 'init',value: function init () {// 绑定事件var isTouch = this.state.isTouch;this.el.addEventListener( isTouch ? 'touchstart' : 'mousedown', this.onStart.bind( this ), false );this.el.addEventListener( isTouch ? 'touchmove' : 'mousemove', this.onMove.bind( this ), false );this.el.addEventListener( isTouch ? 'touchend' : 'mouseup', this.onEnd.bind( this ), false );this.el.addEventListener( isTouch ? 'touchcancel' : 'mouseout', this.onEnd.bind( this ), false );}}, {key: 'destroyed',value: function destroyed () {if ( this.el ) {var isTouch = this.state.isTouch;this.el.removeEventListener( isTouch ? 'touchstart' : 'mousedown', this.onStart.bind( this ) );this.el.removeEventListener( isTouch ? 'touchmove' : 'mousemove', this.onMove.bind( this ) );this.el.removeEventListener( isTouch ? 'touchend' : 'mouseup', this.onEnd.bind( this ) );this.el.removeEventListener( isTouch ? 'touchcancel' : 'mouseout', this.onEnd.bind( this ) );}}}, {key: 'clear',value: function clear () {// 清除画布this.state.index = -1;this.state.undopath = [];this.ctx.clearRect( 0, 0, this.el.width, this.el.height );}}, {key: 'undo',value: function undo () {// 撤销this.state.index >= 0 && --this.state.index;var undopath = this.state.undopath;this.state.undopath.pop();this.ctx.clearRect( 0, 0, this.el.width, this.el.height );if ( undopath ) {this.ctx.beginPath();for ( var z = 0; z < undopath.length; ++z ) {this.ctx.moveTo( undopath[z][0].x, undopath[z][0].y );this.ctx.lineWidth = undopath[z][0].lineWidth;this.ctx.strokeStyle = undopath[z][0].strokeStyle;for ( var i = 0; i < undopath[z].length; ++i ) {this.ctx.lineTo( undopath[z][i].x, undopath[z][i].y );}}this.ctx.stroke();this.ctx.closePath();} else {this.state.undopath = [];}}}] );return Draw;}();return Draw;} ) ) );
