JS實現移動端在線簽協議功能

2019-11-19 10:59:39

字體：大中小

來源：轉載

供稿：網友

在一個風和日麗的下午，剛準備下班，突然接到需求說要做一個在線簽協議功能，當時心里想著不就百度一頓拷貝就完事了嗎(因為我沒用過canvas，所謂初生牛犢不怕虎 )，誰知做起來如此吃力，下面就來記錄下歷程。

協議模板

分析

如上圖，需要做的就是做一個簽字板可以在上面寫字，寫完后點擊完成可以生成如上圖的圖片所示，把簽好的字放到指定的位置。

做這個第一反應肯定就是使用canvas繪制路徑

我的思路是:

一個字一個字寫，每寫一個字點一下記錄，最后拼接，但想到用戶體驗問題就pass了這個思路。

最后的思路：一行可以寫很多個字，可以讓用戶滑動canvas，一直寫下去(因為協議模板最后還要抄寫一段話)

canvas繪制路徑--實現簽名功能

<canvas id="canvas" style="top:0">您的手機不支持在線簽署</canvas>const canvasPaint = {};//定義一個全局對象，把canvas的各種狀態存進去canvasPaint.canvas = document.getElementById("canvas");canvasPaint.ctx = document.getElementById("canvas").getContext("2d");canvasPaint.ctx.lineCap = 'round';//讓結束線帽呈現圓滑狀canvasPaint.ctx.lineJoin = 'round';//交匯時呈現圓滑狀canvasPaint.ctx.strokeWidth = 5;//描邊寬度canvasPaint.ctx.lineWidth = 5;//線條寬度

初始化好畫布后，我們需要監聽畫布上的滑動事件

canvasPaint.canvas.addEventListener('touchstart', startEventHandler, {passive: false});function startEventHandler(event) { event.preventDefault(); canvasPaint.ctx.beginPath();//每次都是一個新路徑,不寫會和上個字的最后一筆連起來 canvasPaint.canvas.addEventListener('touchmove', moveEventHandler, {passive: false}); canvasPaint.canvas.addEventListener('touchend', endEventHandler, {passive: false});}

passive: false 和 event.preventDefault() 這兩個是絕配哦， event.preventDefault() 阻止默認行為，防止在畫布上寫字時觸發了瀏覽器自帶的下拉動作之類的。那 passive: false 是谷歌56版本后提出的新屬性，設置為 false 就是告訴瀏覽器我有阻止默認行為的代碼，剛開始不要給我滑動，你需要執行我的 event.preventDefault() 這句代碼，如果設置為了 true ,瀏覽器會自動忽略這句代碼，從而不能阻止成功，默認是 true ，所以這里就是坑之一了。

我們繼續編寫移動劃線邏輯

function moveEventHandler(event) { event.preventDefault(); var coverPos = canvasPaint.canvas.getBoundingClientRect(); canvasPaint.mouseX = event.clientX - coverPos.left; canvasPaint.mouseY = event.clientY - coverPos.top; if (canvasPaint.canPaint) {//后續為拖動畫布功能設置的狀態 canvasPaint.ctx.lineTo(//使用lineTo將移動過的坐標繪制成線 canvasPaint.mouseX, canvasPaint.mouseY ); canvasPaint.ctx.stroke();//繪制 }}function endEventHandler(event) { event.preventDefault(); //抬起手指時取消move和end事件的監聽 canvasPaint.canvas.removeEventListener('touchmove', moveEventHandler, false); canvasPaint.canvas.removeEventListener('touchend', endEventHandler, false);}

canvas--清除屏幕功能

這個功能比較簡單就一句話

function clearCanvas() { canvasPaint.ctx.clearRect(0, 0, canvasPaint.canvas.width, canvasPaint.canvas.height);}

提交簽名功能

首先需要將畫布上的文字轉換為img對象，然后使用drawImage繪制到協議上去

preLoadImg(['/assets/index/images/agree.jpg', canvasPaint.canvas.toDataURL()], result);//agree.jpg為協議名，canvasPaint.canvas.toDataURL()就是簽好的字轉換為base64的結果function preLoadImg(source, callBack, args) { var pr = []; source.forEach(url => { var p = loadImage(url) .then(function (img) { return img; }) .catch(function (err) { console.log(err); }); pr.push(p); }); Promise.all(pr) .then(function (imgArray) { callBack(imgArray, args); });}function loadImage(url) { return new Promise((resolve, reject) => { var img = new Image(); img.onload = function () { resolve(img); }; img.onerror = reject; img.src = url; });}

由于img賦值src是異步的，我們必須要一個完整的image對象，所以我們使用promise包裝，使得我們所有圖片都轉換完之后再將結果傳入回調函數(result)中

function result(imgArr) { drawName(imgArr);}function drawName(imgArr) { //繪制名字和底部的名字和日期 canvasPaint.canvas2 = document.getElementById('canvas2'); canvasPaint.context2 = canvasPaint.canvas2.getContext('2d'); canvasPaint.ratio = canvasPaint.canvas.height / canvasPaint.canvas.width; //計算畫布比例 canvasPaint.context2.drawImage(imgArr[0], 0, 0, 500, 707);//img0是底圖原協議 canvasPaint.context2.save(); canvasPaint.context2.translate(50, 190); canvasPaint.context2.rotate(270 * Math.PI / 180); canvasPaint.context2.drawImage(imgArr[1], 80, 50, 33, 33 * canvasPaint.ratio);//畫反轉后的名字 canvasPaint.context2.restore(); canvasPaint.context2.save(); canvasPaint.context2.translate(67, 723);//下方的字 canvasPaint.context2.rotate(270 * Math.PI / 180); canvasPaint.context2.drawImage(imgArr[1], 80, 50, 33, 33 * canvasPaint.ratio);//畫反轉后的名字 canvasPaint.context2.restore(); canvasPaint.context2.save(); canvasPaint.context2.translate(400, 625);//下方的字 canvasPaint.context2.font = "11px 微軟雅黑"; canvasPaint.context2.fillStyle = "#000"; canvasPaint.context2.textAlign = "center"; canvasPaint.context2.textBaseline = "middle"; var time = new Date().toLocaleString().split(' ')[0]; canvasPaint.context2.fillText(time, 0, 0); canvasPaint.context2.restore(); prevDrawStatement();}

這里最主要的還是要理解下畫布的rotate和translate方法，就可以把文字旋轉任意角度和放到任意位置了

長字手寫--畫布拖動

上面簽字完成后，我們其實已經用了另一個canvas合成了文字和原協議，現在我們要做無限拖動功能，其實也很簡單。

在此之前我們需要清空之前的畫布

function prevDrawStatement() { clearCanvas();//清除畫布 canvasPaint.finish.innerHTML = "提交抄寫"; canvasPaint.pencilBtn.style.display = 'block'; canvasPaint.secondState.style.display = 'block'; canvasPaint.tips.innerHTML = "(最后一步)請抄寫屏幕上方引號內的確認語句"; canvasPaint.tips.style.color = 'red'; setTimeout(function () { canvasPaint.tips.style.color = '#666'; }, 2000); state = STATEMENT;//開始寫句子}

右上角有個移動簽字板功能，這里實現的是左右移動，相關代碼如下

function togglePencil() { if (canvasPaint.canPaint) { canvasPaint.canPaint = false; canvasPaint.pencilBtn.innerText = "使用簽字筆"; //不能簽字時應該把開始寫字事件去掉，同時加上document事件 canvasPaint.canvas.removeEventListener('touchstart', startEventHandler, false); document.addEventListener('touchstart', documentStartEventHandler, {passive: false}); } else { canvasPaint.canPaint = true; canvasPaint.pencilBtn.innerText = "移動簽字板"; //能簽字時應該把開始寫字事件綁定上去，同時去掉document事件 canvasPaint.canvas.addEventListener('touchstart', startEventHandler, {passive: false}); document.removeEventListener('touchstart', documentStartEventHandler, false); }}function documentStartEventHandler(event) { event.preventDefault(); canvasPaint.y = event.clientY; canvasPaint.top = parseFloat(canvasPaint.canvas.style.top);//畫板距離頂部的值 document.addEventListener('touchmove', documentMoveEventHandler, {passive: false}); document.addEventListener('touchend', documentEndEventHandler, {passive: false});}function documentMoveEventHandler(event) { event.preventDefault(); canvasPaint.newY = event.clientY - canvasPaint.y; if (!canvasPaint.canPaint) { canvasPaint.canvas.style.top = canvasPaint.newY + canvasPaint.top + 'px'; if (parseFloat(canvasPaint.canvas.style.top) > 0) {//限制邊界  canvasPaint.canvas.style.top = 0 + 'px'; } }}function documentEndEventHandler(event) { event.preventDefault();}

合成長句到協議中并顯示最終圖片

提交抄寫按鈕點擊后執行下面的函數

function statementDraw(imgArr) { canvasPaint.context2.save(); canvasPaint.context2.translate(52, 690); canvasPaint.context2.rotate(270 * Math.PI / 180); canvasPaint.context2.drawImage(imgArr[0], 80, 50, 33, 33 * canvasPaint.ratio);//畫反轉后的名字 canvasPaint.context2.restore(); console.log(canvasPaint.canvas2.toDataURL()); document.getElementById('resultImg').setAttribute('src', canvasPaint.canvas2.toDataURL()); document.getElementById('resultImg').style.position = 'absolute'; document.getElementById('resultImg').style.left = 0; document.getElementById('resultImg').style.top = 0; document.getElementById('resultImg').style.zIndex = 50;}