点击交互
使用 isPointInPath(x, y) 判断鼠标点击位置在不在图形内
<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head><body><canvas id="canvas" style="border:1px solid #ccc;display:block;margin:10px auto;"></canvas></div><script>const canvas = document.getElementById('canvas')canvas.width = 800canvas.height = 800const context = canvas.getContext('2d')const balls = []for(let i = 0; i < 10; i++) {const ball = {x: Math.random() * canvas.width,y: Math.random() * canvas.height,r: Math.random() * 50 + 20}balls[i] = ball}draw()canvas.addEventListener('mouseup', detect)function draw() {for(let i = 0; i < balls.length; i++) {context.beginPath()context.arc(balls[i].x, balls[i].y, balls[i].r, 0, Math.PI*2)context.fillStyle = '#058'context.fill()}}function detect(event) {const x = event.clientX - canvas.getBoundingClientRect().leftconst y = event.clientY - canvas.getBoundingClientRect().topfor (let i = 0; i < balls.length; i++) {context.beginPath()context.arc(balls[i].x, balls[i].y, balls[i].r, 0, Math.PI * 2)if (context.isPointInPath(x, y)) {context.fillStyle = 'red'context.fill()}}}</script>
</body></html>图示：
鼠标移动事件
<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head><body><canvas id="canvas" style="border:1px solid #ccc;display:block;margin:10px auto;"></canvas></div><script>const canvas = document.getElementById('canvas')canvas.width = 800canvas.height = 800const context = canvas.getContext('2d')const balls = []for(let i = 0; i < 10; i++) {const ball = {x: Math.random() * canvas.width,y: Math.random() * canvas.height,r: Math.random() * 50 + 20}balls[i] = ball}draw()canvas.addEventListener('mousemove', detect)function draw(x, y) {context.clearRect(0, 0, canvas.width, canvas.height)for(let i = 0; i < balls.length; i++) {context.beginPath()context.arc(balls[i].x, balls[i].y, balls[i].r, 0, Math.PI*2)if(context.isPointInPath(x, y)) {context.fillStyle = 'red'} else {context.fillStyle = '#058'}context.fill()}}function detect(event) {const x = event.clientX - canvas.getBoundingClientRect().leftconst y = event.clientY - canvas.getBoundingClientRect().topdraw(x, y)}</script>
</body></html>图示:
在Canvas上使用HTML元素进行交互
<!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>#canvas-wrapper {width: 1200px;height: 800px;position: relative;margin: 20px auto;}#canvas {border: 1px solid #aaa;}#controller {position: absolute;top: 30px;left: 30px;background-color: rgba(0, 85, 116, 0.7);padding: 5px 20px 25px 20px;border-radius: 10px 10px;}#controller h1 {color: white;font-weight: bold;font-family: Microsoft Yahei;}#controller #canvas-btn {display: inline-block;background-color: #8b0;color: white;font-size: 14px;padding: 5px 15px;border-radius: 6px;text-decoration: none;margin-top: 10px;margin-right: 20px;}#controller #canvas-btn:hover {background-color: #7a0;}#controller .color-btn {display: inline-block;font-size: 14px;padding: 5px 15px;border-radius: 6px;text-decoration: none;margin-top: 10px;margin-right: 5px;}#white-color-btn {background: white;}#black-color-btn {background: black;}</style>
</head><body><div id="canvas-wrapper"><canvas id="canvas"></canvas><div id="controller"><h1>Canvas 绘图之旅</h1><a href="#" id="canvas-btn">停止运动</a><a href="#" class="color-btn" id="white-color-btn"> </a><a href="#" class="color-btn" id="black-color-btn"> </a></div></div><script>const canvas = document.getElementById('canvas')canvas.width = 1200canvas.height = 800const context = canvas.getContext('2d')const balls = []let isMoving = truelet themeColor = 'white'for(let i = 0; i < 100; i++) {const R = Math.floor(Math.random() * 255)const G = Math.floor(Math.random() * 255)const B = Math.floor(Math.random() * 255)const radius = Math.random() * 50 + 20const ball = {color: `rgb(${R}, ${G}, ${B})`,radius,x: Math.random() * (canvas.width - 2*radius) + radius,y: Math.random() * (canvas.height - 2*radius) + radius,vx: (Math.random() * 5 + 5) * Math.pow(-1, Math.floor(Math.random()*100)),vy: (Math.random() * 5 + 5) * Math.pow(-1, Math.floor(Math.random() * 100)),}balls[i] = ball}setInterval(function() {draw(context)if(isMoving) {update(canvas.width, canvas.height)}}, 50)document.getElementById('canvas-btn').onclick = function() {if (isMoving) {isMoving = falsethis.text = '开始运动'} else {isMoving = truethis.text = '停止运动'}}document.getElementById('white-color-btn').onclick = function() {themeColor = 'white'return false}document.getElementById('black-color-btn').onclick = function () {themeColor = 'black'return false}function draw(cxt) {cxt.clearRect(0, 0, cxt.canvas.width, cxt.canvas.height)if (themeColor === 'black') {cxt.fillStyle = 'black'cxt.fillRect(0, 0, cxt.canvas.width, cxt.canvas.height)}for(let i = 0; i < balls.length; i++) {cxt.fillStyle = balls[i].colorcxt.beginPath()cxt.arc(balls[i].x, balls[i].y, balls[i].radius, 0, Math.PI*2)cxt.closePath()cxt.fill()}}function update(canvasWidth, canvasHeight) {for (let i = 0; i < balls.length; i++) {balls[i].x += balls[i].vxballs[i].y += balls[i].vyif (balls[i].x - balls[i].radius <= 0) {balls[i].vx = -balls[i].vxballs[i].x = balls[i].radius}if (balls[i].x + balls[i].radius >= canvasWidth) {balls[i].vx = -balls[i].vxballs[i].x = canvasWidth - balls[i].radius}if (balls[i].y - balls[i].radius <= 0) {balls[i].vy = -balls[i].vyballs[i].y = balls[i].radius}if (balls[i].y - balls[i].radius >= canvasHeight) {balls[i].vy = -balls[i].vyballs[i].y = canvasHeight - balls[i].radius}}}</script>
</body></html>图示：
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