js实现canvas截图功能

关键代码

使用canvas的导出功能和drawImage函数

class CropShape{cropShape(shape){let {x,y,w,h} = shapeconsole.log(x,y,w,h)const roiCanvas = document.createElement('canvas');document.getElementById('app').append(roiCanvas)const roiCtx = roiCanvas.getContext('2d');roiCanvas.width = w;roiCanvas.height = h;roiCtx.drawImage(this.stage.image, x, y, w, h, 0, 0, w, h);const dataURL = roiCanvas.toDataURL('image/png');return dataURL;}downloadImage(dataURL, filename) {const link = document.createElement('a');link.href = dataURL;link.download = filename;document.body.appendChild(link);link.click();document.body.removeChild(link);}
}

使用示例

let cimg = new CropShape()
let img = cimg.cropShape({x:1,y:1,w:10,h:10
})
cimg.downloadImage(cimg,'result.png')

绘制roi代码 demo

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Canvas Screenshot with ROI</title><style>canvas {border: 1px solid black;}</style>
</head>
<body><input type="file" id="upload" accept="image/*"><canvas id="canvas"></canvas><canvas id="roiCanvas" style="display:none;"></canvas><img id="croppedImage" alt="Cropped Image" /><script>const upload = document.getElementById('upload');const canvas = document.getElementById('canvas');const ctx = canvas.getContext('2d');const roiCanvas = document.getElementById('roiCanvas');const roiCtx = roiCanvas.getContext('2d');const croppedImage = document.getElementById('croppedImage');let image = new Image();let startX, startY, endX, endY;let isDrawing = false;upload.addEventListener('change', function(event) {const file = event.target.files[0];const reader = new FileReader();reader.onload = function(e) {image.src = e.target.result;};reader.readAsDataURL(file);});image.onload = function() {canvas.width = image.width;canvas.height = image.height;ctx.drawImage(image, 0, 0);};canvas.addEventListener('mousedown', function(event) {startX = event.offsetX;startY = event.offsetY;isDrawing = true;});canvas.addEventListener('mousemove', function(event) {if (isDrawing) {endX = event.offsetX;endY = event.offsetY;draw();}});canvas.addEventListener('mouseup', function(event) {if (isDrawing) {endX = event.offsetX;endY = event.offsetY;isDrawing = false;cropImage();}});function draw() {ctx.clearRect(0, 0, canvas.width, canvas.height);ctx.drawImage(image, 0, 0);ctx.strokeStyle = 'red';ctx.lineWidth = 2;ctx.strokeRect(startX, startY, endX - startX, endY - startY);}function cropImage() {const width = endX - startX;const height = endY - startY;roiCanvas.width = width;roiCanvas.height = height;roiCtx.drawImage(canvas, startX, startY, width, height, 0, 0, width, height);const dataURL = roiCanvas.toDataURL();croppedImage.src = dataURL;croppedImage.style.display = 'block';}</script>
</body>
</html>