html代码
todo 实现画矩形框，圆形roi
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Canvas Image Viewer</title>
<style>
canvas {
border: 1px solid black;
}
</style>
</head>
<body>
<div>
<button id="loadImageButton">Load Image</button>
</div>
<canvas id="mainCanvas" width="600" height="400"></canvas>
<script>
const canvas = document.getElementById('mainCanvas');
const ctx = canvas.getContext('2d');
let imageObj = new Image();
let imageWidth;
let imageHeight;
let scale = 1;
let offsetX = 0;
let offsetY = 0;
canvas.addEventListener('mousedown', mouseDownListener);
canvas.addEventListener('mouseup', mouseUpListener);
canvas.addEventListener('mousemove', mouseMoveListener);
canvas.addEventListener('mousewheel', mouseWheelListener);
document.getElementById('loadImageButton').addEventListener('click', loadImage);
function loadImage() {
const input = document.createElement('input');
input.type = 'file';
input.accept = 'image/*';
input.click();
input.onchange = e => {
const file = e.target.files[0];
const reader = new FileReader();
reader.onload = readerEvent => {
const url = readerEvent.target.result;
imageObj.src = url;
};
reader.readAsDataURL(file);
};
}
let isDragging = false;
let lastX;
let lastY;
function mouseDownListener(e) {
let rect = canvas.getBoundingClientRect();
isDragging = true;
lastX = e.clientX - rect.left;
lastY = e.clientY - rect.top;
}
function mouseUpListener(e) {
isDragging = false;
}
function mouseMoveListener(e) {
if (isDragging) {
let rect = canvas.getBoundingClientRect();
offsetX -= (e.clientX - rect.left) - lastX;
offsetY -= (e.clientY - rect.top) - lastY;
lastX = e.clientX - rect.left;
lastY = e.clientY - rect.top;
ctx.clearRect(0, 0, canvas.width, canvas.height);
drawImage();
}
}
function mouseWheelListener(e) {
let delta = Math.max(-1, Math.min(1, (e.wheelDelta || -e.detail)));
if (scale > 0.1 && scale < 10 && delta < 0) {
scale *= 0.9;
}
if (scale > 0.1 && scale < 10 && delta > 0) {
scale *= 1.1;
}
ctx.clearRect(0, 0, canvas.width, canvas.height);
drawImage();
}
function drawImage() {
ctx.drawImage(imageObj,
-offsetX,
-offsetY,
imageWidth * scale,
imageHeight * scale);
}
imageObj.onload = () => {
imageWidth = imageObj.width;
imageHeight = imageObj.height;
drawImage();
}
</script>
</body>
</html>
