/**
* 默认画笔线宽
* @type {number}
*/
var defaultStrokeWidth = 1; //画矩形选取框的线宽
/**
* 选取划线的canvasExt
* @type {{drawRect: canvasExt.drawRect}}
*/
var canvasExt = {
/**
*  画矩形
* @param canvasId canvasId
* @param penColor 画笔颜色
* @param strokeWidth 线宽
*/
drawRect: function (canvasId, penColor, strokeWidth) {
var that = this;
that.penColor = penColor;
that.penWidth = strokeWidth;
var canvas = document.getElementById(canvasId);
//canvas 的矩形框
var canvasRect = canvas.getBoundingClientRect();
//canvas 矩形框的左上角坐标
var canvasLeft = canvasRect.left;
var canvasTop = canvasRect.top;
// 要画的矩形的起点 xy
var x = 0;
var y = 0;
//鼠标点击按下事件，画图准备
canvas.onmousedown = function (e) {
//设置画笔颜色和宽度
var color = that.penColor;
var penWidth = that.penWidth;
// 确定起点
x = e.clientX - canvasLeft;
y = e.clientY - canvasTop;
// 添加layer
$("#" + canvasId).addLayer({
type: 'rectangle',
strokeStyle: color,
strokeWidth: penWidth,
name: 'areaLayer',
fromCenter: false,
x: x, y: y,
width: 1,
height: 1
});
// 绘制
$("#" + canvasId).drawLayers();
$("#" + canvasId).saveCanvas();
//鼠标移动事件，画图
canvas.onmousemove = function (e) {
// 要画的矩形的宽高
var width = e.clientX - canvasLeft - x;
var height = e.clientY - canvasTop - y;
// 清除之前画的
$("#" + canvasId).removeLayer('areaLayer');
$("#" + canvasId).addLayer({
type: 'rectangle',
strokeStyle: color,
strokeWidth: penWidth,
name: 'areaLayer',
fromCenter: false,
x: x, y: y,
width: width,
height: height
});
$("#" + canvasId).drawLayers();
}
};
//鼠标抬起
canvas.onmouseup = function (e) {
var color = that.penColor;
var penWidth = that.penWidth;
canvas.onmousemove = null;
var width = e.clientX - canvasLeft - x;
var height = e.clientY - canvasTop - y;
$("#" + canvasId).removeLayer('areaLayer');
$("#" + canvasId).addLayer({
type: 'rectangle',
strokeStyle: color,
strokeWidth: penWidth,
name: 'areaLayer',
fromCenter: false,
x: x, y: y,
width: width,
height: height
});
$("#" + canvasId).drawLayers();
$("#" + canvasId).saveCanvas();
// 把body转成canvas
html2canvas(document.body, {
scale: 1,
// allowTaint: true,
useCORS: true,  //跨域使用
// foreignObjectRendering: true
}).then(canvas => {
var capture_x, capture_y
if (width > 0) {
//从左往右画
capture_x = x + that.penWidth
} else {
//从右往左画
capture_x = x + width + that.penWidth
}
if (height > 0) {
//从上往下画
capture_y = y + that.penWidth
} else {
//从下往上画
capture_y = y + height + that.penWidth
}
printClip(canvas, capture_x, capture_y, Math.abs(width), Math.abs(height))
});
// 移除画的选取框
$("#" + canvasId).removeLayer('areaLayer');
// 隐藏用于华画取框的canvas
$("#" + canvasId).hide()
}
}
};
/**
* 选取截屏
* @param canvasId
*/
function clipScreenshots(canvasId) {
canvasExt.drawRect(canvasId, "red", defaultStrokeWidth);
}
/**
* 打印截取区域
* @param canvas 截取的canvas
* @param capture_x 截取的起点x
* @param capture_y 截取的起点y
* @param capture_width 截取的起点宽
* @param capture_height 截取的起点高
*/
function printClip(canvas, capture_x, capture_y, capture_width, capture_height) {
// 创建一个用于截取的canvas
var clipCanvas = document.createElement('canvas')
clipCanvas.width = capture_width
clipCanvas.height = capture_height
// 截取
clipCanvas.getContext('2d').drawImage(canvas, capture_x, capture_y, capture_width, capture_height, 0, 0, capture_width, capture_height)
var clipImgBase64 = clipCanvas.toDataURL()
// // 生成图片
// var clipImg = new Image()
// clipImg.src = clipImgBase64
// var con = confirm('打印截图吗?取消则保存截图')
// if (con) {
//   $(clipImg).print()
// } else {
//   downloadIamge(clipImgBase64)
// }
// alert二维码解析内容
const qrcode = new QRCode.Decoder();
qrcode
.scan(clipImgBase64)
.then(r###lt => {
console.log(r###lt.data);
alert(r###lt.data)
})
.catch(error => {
console.error(error);
alert("出错：" + error)
});
}
/**
* 下载保存图片
* @param imgUrl 图片地址
*/
function downloadIamge(imgUrl) {
// 图片保存有很多方式，这里使用了一种投机的简单方法。
// 生成一个a元素
var a = document.createElement('a')
// 创建一个单击事件
var event = new MouseEvent('click')
// 生成文件名称
var timestamp = new Date().getTime();
var name = imgUrl.substring(22, 30) + timestamp + '.png';
a.download = name
// 将生成的URL设置为a.href属性
a.href = imgUrl;
// 触发a的单击事件 开始下载
a.dispatchEvent(event);
}