幀動(dòng)畫的實(shí)現(xiàn)，關(guān)鍵是Canvas API ctx.drawImage() （9個(gè)參數(shù)）和 setInterval 定時(shí)器。
設(shè)置圖片的視圖窗口，每次執(zhí)行定時(shí)任務(wù)，位移展示下一幀圖片。
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>幀動(dòng)畫</title>
</head>
<body>
<canvas id="canvas" width="400" height="300"></canvas>
<div class="">
<button class="start-btn" type="button">重新吃</button>
<button class="end-btn" type="button">不吃了</button>
<button class="pause-btn" type="button">歇一歇</button>
<button class="continue-btn" type="button">繼續(xù)吃</button>
</div>
<script type="text/javascript">
const canvas = document.getElementById("canvas")
canvas.style.border = "1px solid black"
const ctx = canvas.getContext("2d")
const img = new Image() // 創(chuàng)建圖片對(duì)象
let timer // 定時(shí)器標(biāo)識(shí)符
let millisec = 300 // 執(zhí)行時(shí)間間隔
let colIndex = 0 // 列數(shù)
let rowIndex = 0 // 行數(shù)
const timerFun = () => { // 聲明定時(shí)器執(zhí)行函數(shù)
console.log("設(shè)置定時(shí)器");
ctx.clearRect(0, 0, canvas.style.width, canvas.style.height) // 清除畫布
if (rowIndex < 3) { // 如果是前5幀
ctx.drawImage(img, colIndex * 240, rowIndex * 240, 200, 200, 50, 50, 200, 200) // 圖片對(duì)象，x坐標(biāo)，y坐標(biāo)（注：圖片上定位的坐標(biāo)），width，height（圖片上截取的大?。瑇坐標(biāo)，y坐標(biāo)（注：圖片在畫布上的起點(diǎn)，即左上角），width，height（縮放，不是裁剪）
colIndex++ // 下一幀
if (colIndex > 4) {
colIndex = 0
rowIndex++
}
} else {
colIndex = 0
rowIndex = 0
}
}
img.onload = () => {
timer = setInterval(timerFun, millisec)
}
img.src = "image/apple.jpg"
const startBtn = document.getElementsByClassName('start-btn')[0]
const endBtn = document.getElementsByClassName('end-btn')[0]
const pauseBtn = document.getElementsByClassName('pause-btn')[0]
const continueBtn = document.getElementsByClassName('continue-btn')[0]
startBtn.addEventListener('click', () => {
console.log("點(diǎn)擊開始", timer)
clearInterval(timer)
colIndex = 0 // 列數(shù)
rowIndex = 0 // 行數(shù)
timer = setInterval(timerFun, millisec)
})
endBtn.addEventListener('click', () => {
console.log("點(diǎn)擊結(jié)束", timer)
clearInterval(timer)
colIndex = 0
rowIndex = 0
ctx.drawImage(img, colIndex * 240, rowIndex * 240, 200, 200, 50, 50, 200, 200)
timer = 0
})
pauseBtn.addEventListener('click', () => {
console.log("點(diǎn)擊暫停", timer)
clearInterval(timer)
timer = 0
})
continueBtn.addEventListener('click', () => {
if (timer) {
alert('吃著呢，別催')
return
}
console.log("點(diǎn)擊繼續(xù)", timer)
timer = setInterval(timerFun, millisec)
})
</script>
</body>
</html>
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