html代碼
todo 實現(xiàn)畫矩形框，圓形roi文章來源地址http://www.zghlxwxcb.cn/news/detail-848156.html
<!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="900" height="800"></canvas>
<div>
<span>坐標(biāo)</span>
<span id="imageXY"></span>
<div>
<span id="imagePix"></span>
</div>
</div>
<script>
const canvas = document.getElementById('mainCanvas');
const ctx = canvas.getContext('2d');
ctx.imageSmoothingEnabled = false;
let imageObj = new Image();
let imageWidth;
let imageHeight;
let scale = 1;
let offsetX = 0;
let offsetY = 0;
let pixdata;
canvas.addEventListener('mousedown', mouseDownListener);
canvas.addEventListener('mouseup', mouseUpListener);
canvas.addEventListener('mousemove', mouseMoveListener);
canvas.addEventListener('mousewheel', mouseWheelListener);
document.getElementById('loadImageButton').addEventListener('click', loadImage);
function initPixData(image){
const canvasHide = document.createElement('canvas');
const context = canvasHide.getContext('2d');
canvasHide.width = image.width;
canvasHide.height = image.height;
context.drawImage(image, 0, 0);
const imageData = context.getImageData(0, 0, image.width, image.height);
pixdata = imageData.data;
console.log(pixdata)
}
function getPixelValue(x, y) {
let pixelValue;
if (pixdata.length === 4) {
pixelValue = {
red: pixel[0],
green: pixel[1],
blue: pixel[2],
alpha: pixel[3]
};
} else if (ipixdata.length === 1) {
pixelValue = {
gray: pixel[0]
};
} else {
throw new Error('Unsupported image format');
}
return pixelValue;
}
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();
}
showImageXY(e);
}
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 createBlock(a, b, r) {
let rect = canvas.getBoundingClientRect();
let canvasX = (a * scale) + offsetX + rect.left;
let canvasY = (b * scale) + offsetY + rect.top;
let radius=r*scale;
ctx.beginPath();
ctx.fillStyle = 'red';
ctx.arc(canvasX, canvasY, radius, 0, Math.PI * 2);
ctx.fill();
}
function drawImage() {
ctx.drawImage(imageObj,
offsetX,
offsetY,
imageWidth * scale,
imageHeight * scale);
createBlock(200,200,200)
}
//計算當(dāng)前鼠標(biāo)坐標(biāo)對應(yīng)的圖片里的像素坐標(biāo)
function showImageXY(e) {
let rect = canvas.getBoundingClientRect();
let x=(e.clientX - rect.left- offsetX)/scale
let y=(e.clientY- rect.top - offsetY)/scale
x=Math.round(x)
y=Math.round(y)
if(x<0 || x>imageWidth){
x="-"
}
if(y<0 || y>imageHeight){
y="-"
}
if(!(x=='-'|| y=='-')){
showImagePixVal(x,y);
}
document.getElementById("imageXY").innerText = `x=${x} y=${y} xInCanvas=${offsetX} yInCanvas=${offsetY} width=${imageWidth} height=${imageHeight}`;
}
function showImagePixVal(x,y){
let idx=((y * (imageWidth * 4)) + (x * 4));
if(pixdata){
let r=pixdata[idx]
let g=pixdata[idx+1]
let b=pixdata[idx+2]
let a=pixdata[idx+3]
document.getElementById("imagePix").innerText = `r=${r} g=${g} b=$ a=${a}`;
}
}
imageObj.onload = () => {
imageWidth = imageObj.width;
imageHeight = imageObj.height;
drawImage();
initPixData(imageObj);
}
</script>
</body>
</html>
文章來源：http://www.zghlxwxcb.cn/news/detail-848156.html
到了這里，關(guān)于js使用canvas實現(xiàn)圖片鼠標(biāo)滾輪放大縮小拖拽預(yù)覽，顯示像素坐標(biāo)，顯示像素值的文章就介紹完了。如果您還想了解更多內(nèi)容，請在右上角搜索TOY模板網(wǎng)以前的文章或繼續(xù)瀏覽下面的相關(guān)文章，希望大家以后多多支持TOY模板網(wǎng)！
