canvas 實現簽名效果
阿新 • • 發佈:2021-09-15
效果圖
概述
線上簽名,現在在很多場景下都能看到,而且在移動端見的比較多。
用canvas
和svg
都可以實現,而且跨平臺能力也很好。
canvas
基於畫素,提供 2D 繪製函式,提供的功能更原始,適合畫素處理、動態渲染和大量資料繪製,可控性高,繪製完了基本不記錄過程,繪圖效能會更好一點,各大廠商也早都實現了canvas
的硬體加速機制。而且能夠以.png
或.jpg
格式儲存結果影象svg
為向量,提供一序列圖形元素,功能更完善,建立了一大堆可互動物件,本性長於互動,但效能會弱些,更適合靜態圖片展示,高保真文件檢視和列印的應用場景。
兩者各有自己擅長的領域,基於以上,以下是用canvas
程式碼
html結構
<div id="canvas">
<p id="clearCanvas">清除</p>
<p id="saveCanvas">儲存</p>
</div>
css樣式
html,
body {
width: 100%;
height: 100%;
}
* {
margin: 0;
padding: 0;
}
#canvas {
position: relative;
width: 100%;
height: 100%;
}
#canvas canvas {
display: block;
}
#clearCanvas,
#saveCanvas {
position: absolute;
bottom: 0;
z-index: 1;
width: 50%;
height: 40px;
border: 1px solid #dedede;
line-height: 40px;
text-align: center;
}
#clearCanvas {
left: 0;
}
#saveCanvas {
right: 0;
}
.errorCanvas {
width: 100%;
height: 100%;
text-align: center;
transform: translateY(40%);
}
js內容
window.onload = function () {
new lineCanvas({
el: document.querySelector('#canvas'),
clearEl: document.querySelector('#clearCanvas'),
saveEl: document.querySelector('#saveCanvas'),
// lineWidth: 1, // 線條粗細
// color: 'black', // 線條顏色
// background: '#fff'
});
}
function lineCanvas(obj) {
this.lineWidth = 5;
this.color = '#000';
this.background = '#fff';
for (var i in obj) {
this[i] = obj[i];
};
this.canvas = document.createElement('canvas');
if (!(this.canvas.getContext && this.canvas.getContext('2d'))) {
this.section = document.createElement('section');
this.section.className = 'errorCanvas';
this.section.innerHTML = '對不起,當前瀏覽器暫不支援此功能!'
this.el.prepend(this.section);
return
}
this.canvas.width = this.el.clientWidth;
this.canvas.height = this.el.clientHeight;
this.el.prepend(this.canvas);
this.cxt = this.canvas.getContext('2d');
this.cxt.fillStyle = this.background;
this.cxt.fillRect(0, 0, this.canvas.width, this.canvas.height);
this.cxt.strokeStyle = this.color;
this.cxt.lineWidth = this.lineWidth;
this.cxt.lineCap = 'round'; // 線條末端新增圓形線帽,減少線條的生硬感
this.cxt.lineJoin = 'round'; // 線條交匯時為原型邊角
// 利用陰影,消除鋸齒
this.cxt.shadowBlur = 1;
this.cxt.shadowColor = '#000';
// 開始繪製
this.canvas.addEventListener('touchstart', function (e) {
this.cxt.beginPath();
this.cxt.moveTo(e.changedTouches[0].pageX, e.changedTouches[0].pageY);
}.bind(this), false);
// 繪製中
this.canvas.addEventListener('touchmove', function (e) {
this.cxt.lineTo(e.changedTouches[0].pageX, e.changedTouches[0].pageY);
this.cxt.stroke();
}.bind(this), false);
// 結束繪製
this.canvas.addEventListener('touchend', function (e) {
this.cxt.closePath();
}.bind(this), false);
// 清除畫布
this.clearEl.addEventListener('click', function () {
this.cxt.clearRect(0, 0, this.canvas.width, this.canvas.height);
}.bind(this), false);
// 儲存圖片
this.saveEl.addEventListener('click', function () {
var imgBase64 = this.canvas.toDataURL();
var imgPng = this.canvas.toDataURL('image/png');
var imgJpg = this.canvas.toDataURL('image/jpeg', 0.8);
console.log(imgPng, imgJpg);
}.bind(this), false);
}