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這篇文章將為大家詳細(xì)講解有關(guān)JS怎么實(shí)現(xiàn)移動(dòng)端在線簽協(xié)議功能，小編覺得挺實(shí)用的，因此分享給大家做個(gè)參考，希望大家閱讀完這篇文章后可以有所收獲。
在一個(gè)風(fēng)和日麗的下午，剛準(zhǔn)備下班，突然接到需求說要做一個(gè)在線簽協(xié)議功能，當(dāng)時(shí)心里想著不就百度一頓拷貝就完事了嗎(因?yàn)槲覜]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(xié)議模板
分析
如上圖，需要做的就是做一個(gè)簽字板可以在上面寫字，寫完后點(diǎn)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(gè)第一反應(yīng)肯定就是使用canvas繪制路徑
我的思路是:
一個(gè)字一個(gè)字寫，每寫一個(gè)字點(diǎn)一下記錄，最后拼接，但想到用戶體驗(yàn)問題就pass了這個(gè)思路。
最后的思路：一行可以寫很多個(gè)字，可以讓用戶滑動(dòng)canvas，一直寫下去(因?yàn)閰f(xié)議模板最后還要抄寫一段話)
canvas繪制路徑--實(shí)現(xiàn)簽名功能
<canvas id="canvas" >您的手機(jī)不支持在線簽署</canvas>
const canvasPaint = {};//定義一個(gè)全局對象，把canvas的各種狀態(tài)存進(jìn)去
canvasPaint.canvas = document.getElementById("canvas");
canvasPaint.ctx = document.getElementById("canvas").getContext("2d");
canvasPaint.ctx.lineCap = 'round';//讓結(jié)束線帽呈現(xiàn)圓滑狀
canvasPaint.ctx.lineJoin = 'round';//交匯時(shí)呈現(xiàn)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(jiān)聽畫布上的滑動(dòng)事件
canvasPaint.canvas.addEventListener('touchstart', startEventHandler, {passive: false});
function startEventHandler(event) {
event.preventDefault();
canvasPaint.ctx.beginPath();//每次都是一個(gè)新路徑,不寫會和上個(gè)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(gè)是絕配哦， event.preventDefault() 阻止默認(rèn)行為，防止在畫布上寫字時(shí)觸發(fā)了瀏覽器自帶的下拉動(dòng)作之類的。那 passive: false 是谷歌56版本后提出的新屬性，設(shè)置為 false 就是告訴瀏覽器我有阻止默認(rèn)行為的代碼，剛開始不要給我滑動(dòng)，你需要執(zhí)行我的 event.preventDefault() 這句代碼，如果設(shè)置為了 true ,瀏覽器會自動(dòng)忽略這句代碼，從而不能阻止成功，默認(rèn)是 true ，所以這里就是坑之一了。
我們繼續(xù)編寫移動(dòng)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(xù)為拖動(dòng)畫布功能設(shè)置的狀態(tài)
canvasPaint.ctx.lineTo(//使用lineTo將移動(dòng)過的坐標(biāo)繪制成線
canvasPaint.mouseX,
canvasPaint.mouseY
);
canvasPaint.ctx.stroke();//繪制
}
}
function endEventHandler(event) {
event.preventDefault();
//抬起手指時(shí)取消move和end事件的監(jiān)聽
canvasPaint.canvas.removeEventListener('touchmove', moveEventHandler, false);
canvasPaint.canvas.removeEventListener('touchend', endEventHandler, false);
}canvas--清除屏幕功能
這個(gè)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(zhuǎn)換為img對象，然后使用drawImage繪制到協(xié)議上去
preLoadImg(['/assets/index/images/agree.jpg', canvasPaint.canvas.toDataURL()], result);
//agree.jpg為協(xié)議名，canvasPaint.canvas.toDataURL()就是簽好的字轉(zhuǎn)換為base64的結(jié)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(gè)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(zhuǎn)換完之后再將結(jié)果傳入回調(diào)函數(shù)(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(jì)算畫布比例
canvasPaint.context2.drawImage(imgArr[0], 0, 0, 500, 707);//img0是底圖原協(xié)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(zhuǎn)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(zhuǎn)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(zhuǎn)任意角度和放到任意位置了
長字手寫--畫布拖動(dòng)
上面簽字完成后，我們其實(shí)已經(jīng)用了另一個(gè)canvas合成了文字和原協(xié)議，現(xiàn)在我們要做無限拖動(dòng)功能，其實(shí)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(nèi)的確認(rèn)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(gè)移動(dòng)簽字板功能，這里實(shí)現(xiàn)的是左右移動(dòng)，相關(guān)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(shí)應(yīng)該把開始寫字事件去掉，同時(shí)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(dòng)簽字板";
//能簽字時(shí)應(yīng)該把開始寫字事件綁定上去，同時(shí)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(xié)議中并顯示最終圖片
提交抄寫按鈕點(diǎn)擊后執(zhí)行下面的函數(shù)
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(zhuǎn)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;
}在一個(gè)風(fēng)和日麗的下午，剛準(zhǔn)備下班，突然接到需求說要做一個(gè)在線簽協(xié)議功能，當(dāng)時(shí)心里想著不就百度一頓拷貝就完事了嗎(因?yàn)槲覜]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(xié)議模板
分析
如上圖，需要做的就是做一個(gè)簽字板可以在上面寫字，寫完后點(diǎn)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(gè)第一反應(yīng)肯定就是使用canvas繪制路徑
我的思路是:
一個(gè)字一個(gè)字寫，每寫一個(gè)字點(diǎn)一下記錄，最后拼接，但想到用戶體驗(yàn)問題就pass了這個(gè)思路。
最后的思路：一行可以寫很多個(gè)字，可以讓用戶滑動(dòng)canvas，一直寫下去(因?yàn)閰f(xié)議模板最后還要抄寫一段話)
canvas繪制路徑--實(shí)現(xiàn)簽名功能
<canvas id="canvas" >您的手機(jī)不支持在線簽署</canvas>
const canvasPaint = {};//定義一個(gè)全局對象，把canvas的各種狀態(tài)存進(jìn)去
canvasPaint.canvas = document.getElementById("canvas");
canvasPaint.ctx = document.getElementById("canvas").getContext("2d");
canvasPaint.ctx.lineCap = 'round';//讓結(jié)束線帽呈現(xiàn)圓滑狀
canvasPaint.ctx.lineJoin = 'round';//交匯時(shí)呈現(xiàn)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(jiān)聽畫布上的滑動(dòng)事件
canvasPaint.canvas.addEventListener('touchstart', startEventHandler, {passive: false});
function startEventHandler(event) {
event.preventDefault();
canvasPaint.ctx.beginPath();//每次都是一個(gè)新路徑,不寫會和上個(gè)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(gè)是絕配哦， event.preventDefault() 阻止默認(rèn)行為，防止在畫布上寫字時(shí)觸發(fā)了瀏覽器自帶的下拉動(dòng)作之類的。那 passive: false 是谷歌56版本后提出的新屬性，設(shè)置為 false 就是告訴瀏覽器我有阻止默認(rèn)行為的代碼，剛開始不要給我滑動(dòng)，你需要執(zhí)行我的 event.preventDefault() 這句代碼，如果設(shè)置為了 true ,瀏覽器會自動(dòng)忽略這句代碼，從而不能阻止成功，默認(rèn)是 true ，所以這里就是坑之一了。
我們繼續(xù)編寫移動(dòng)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(xù)為拖動(dòng)畫布功能設(shè)置的狀態(tài)
canvasPaint.ctx.lineTo(//使用lineTo將移動(dòng)過的坐標(biāo)繪制成線
canvasPaint.mouseX,
canvasPaint.mouseY
);
canvasPaint.ctx.stroke();//繪制
}
}
function endEventHandler(event) {
event.preventDefault();
//抬起手指時(shí)取消move和end事件的監(jiān)聽
canvasPaint.canvas.removeEventListener('touchmove', moveEventHandler, false);
canvasPaint.canvas.removeEventListener('touchend', endEventHandler, false);
}canvas--清除屏幕功能
這個(gè)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(zhuǎn)換為img對象，然后使用drawImage繪制到協(xié)議上去
preLoadImg(['/assets/index/images/agree.jpg', canvasPaint.canvas.toDataURL()], result);
//agree.jpg為協(xié)議名，canvasPaint.canvas.toDataURL()就是簽好的字轉(zhuǎn)換為base64的結(jié)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(gè)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(zhuǎn)換完之后再將結(jié)果傳入回調(diào)函數(shù)(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(jì)算畫布比例
canvasPaint.context2.drawImage(imgArr[0], 0, 0, 500, 707);//img0是底圖原協(xié)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(zhuǎn)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(zhuǎn)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(zhuǎn)任意角度和放到任意位置了
長字手寫--畫布拖動(dòng)
上面簽字完成后，我們其實(shí)已經(jīng)用了另一個(gè)canvas合成了文字和原協(xié)議，現(xiàn)在我們要做無限拖動(dòng)功能，其實(shí)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(nèi)的確認(rèn)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(gè)移動(dòng)簽字板功能，這里實(shí)現(xiàn)的是左右移動(dòng)，相關(guān)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(shí)應(yīng)該把開始寫字事件去掉，同時(shí)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(dòng)簽字板";
//能簽字時(shí)應(yīng)該把開始寫字事件綁定上去，同時(shí)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(xié)議中并顯示最終圖片
提交抄寫按鈕點(diǎn)擊后執(zhí)行下面的函數(shù)
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(zhuǎn)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;
}關(guān)于“JS怎么實(shí)現(xiàn)移動(dòng)端在線簽協(xié)議功能”這篇文章就分享到這里了，希望以上內(nèi)容可以對大家有一定的幫助，使各位可以學(xué)到更多知識，如果覺得文章不錯(cuò)，請把它分享出去讓更多的人看到。
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