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| <!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
<style>
html,
body {
margin: 0;
}
.canvas-container,
.canvas-container2 {
display: none;
border: 1px solid #ddd;
}
</style>
</head>
<body>
<div>
<label for="oImageFile">选择图片</label>
<input type="file" id="oImageFile" accept="image/*" />
</div>
<div class="canvas-container">
<canvas id="can"></canvas>
</div>
<img :src="newfile" />
<div class="canvas2-container">
<canvas id="can2"></canvas>
</div>
<script>
const maskOpacity = 0.5
const img = document.querySelector('img')
const oImageFile = document.getElementById('oImageFile')
const oContainer = document.querySelector('.canvas-container')
const oContainer2 = document.querySelector('.canvas2-container')
const oCan = document.getElementById('can')
const oCan2 = document.getElementById('can2')
const ctx = oCan.getContext('2d')
const ctx2 = oCan2.getContext('2d')
let initPos = [] // 记录鼠标的初始位置
let screenShotData = [] //存放所选图片的位置信息
const init = () => {
bindEvent()
}
function handleFileChange(e) {
const file = e.target.files[0]
const reader = new FileReader()
reader.readAsDataURL(file)
reader.onload = function (e) {
img.src = e.target.result
img.onload = function (e) {
const { width, height } = e.target
generateCanvas(oContainer, oCan, width, height)
ctx.drawImage(img, 0, 0, width, height)
drawImageMask(0, 0, width, height, maskOpacity)
}
}
}
function generateCanvas(container, canvas, width, height) {
container.style.wodth = width + 'px'
container.style.width = height + 'px'
canvas.width = width
canvas.height = height
container.style.display = 'block'
}
function bindEvent() {
oImageFile.addEventListener('change', handleFileChange, false)
//添加鼠标监听
oCan.addEventListener('mousedown', handleCanvasMouseDown, false)
}
function handleCanvasMouseDown(e) {
//更新鼠标位置
initPos = [e.offsetX, e.offsetY]
oCan.addEventListener('mousemove', handleCanvasMouseMove, false)
oCan.addEventListener('mouseup', handleCanvasMouseUp, false)
}
function handleCanvasMouseMove(e) {
const endX = e.offsetX
const endY = e.offsetY
const [startX, startY] = initPos
const rectWidth = endX - startX
const rectHeight = endY - startY
const { width, height } = oCan
screenShotData = [startX, startY, rectWidth, rectHeight]
ctx.clearRect(0, 0, width, height)
drawImageMask(0, 0, width, height, maskOpacity)
drawScreenShot(width, height, rectWidth, rectHeight)
}
function handleCanvasMouseUp(e) {
oCan.removeEventListener('mousemove', handleCanvasMouseMove, false)
oCan.removeEventListener('mouseup', handleCanvasMouseUp, false)
drawScreenShotImage(screenShotData)
}
function drawImageMask(x, y, width, height, opacity) {
ctx.fillStyle = `rgba(0, 0, 0, ${opacity})`
ctx.fillRect(x, y, width, height)
}
function drawScreenShot(canwidth, canheight, rectWidth, rectHeight) {
ctx.globalCompositeOperation = 'destination-out'
ctx.fillStyle = `#000`
ctx.fillRect(initPos[0], initPos[1], rectWidth, rectHeight)
ctx.globalCompositeOperation = 'destination-over'
ctx.drawImage(img, 0, 0, canwidth, canheight, 0, 0, canwidth, canheight)
}
function drawScreenShotImage(screenData) {
const data = ctx.getImageData(...screenData)
generateCanvas(oContainer2, oCan2, screenData[2], screenData[3])
ctx2.clearRect(...screenData)
ctx2.putImageData(data, 0, 0)
}
init()
</script>
</body>
</html>
|
