canvas刮刮卡

2021-11-28 17:04:16 作者：互联网
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        html,
        body,
        .img {
            width: 100%;
            height: 100%;
            background-color: blanchedalmond;
        }

        .img {
            background: url("./images/9.jpg") no-repeat center/contain;
        }

        #canvas {
            position: absolute;
            top: 0;
            left: 0;
            z-index: 999;
        }
    </style>
</head>

<body>
    <canvas id="canvas" width="800" height="400">
        您的浏览器不支持canvas，请更换浏览器
    </canvas>
    <div class="img"></div>
    <script>
        window.onload = function () {
            if (canvas.getContext) {
                canvas.width = document.documentElement.clientWidth
                canvas.height = document.documentElement.clientHeight
                const ctx = canvas.getContext('2d')
                const image = new Image()
                image.src = './images/2.jpg'
                image.onload = function () {
                    draw()
                }
                ctx.lineCap = 'round'
                ctx.lineWidth = 40
                canvas.addEventListener('touchstart', (event) => {
                    const x = event.changedTouches[0].clientX
                    const y = event.changedTouches[0].clientY
                    ctx.beginPath()
                    ctx.save()
                    ctx.globalCompositeOperation = 'destination-out'
                    ctx.lineTo(x, y)
                    ctx.stroke()
                    ctx.restore()
                })
                canvas.addEventListener('touchmove', (event) => {
                    const x = event.changedTouches[0].clientX
                    const y = event.changedTouches[0].clientY
                    ctx.save()
                    ctx.globalCompositeOperation = 'destination-out'
                    ctx.lineTo(x, y)
                    ctx.stroke()
                    ctx.restore()
                })
                canvas.addEventListener('touchend', event => {
                    const imageData = ctx.getImageData(0, 0, canvas.width, canvas.height)
                    const allPixel = imageData.data
                    let transparentPixel = 0
                    for (let i = 0; i < allPixel.length / 4; i++) {
                        if (allPixel[4 * i + 3] === 0) {
                            transparentPixel++
                        }
                    }
                    if (transparentPixel * 4 >= allPixel.length / 3) {
                        canvas.style.transition = "all 2s"
                        canvas.style.opacity = 0

                        setTimeout(() => {
                            canvas.style.display = 'none'
                        }, 2000);
                    }

                })

                function draw() {
                    ctx.drawImage(image, 0, 0, canvas.width, canvas.height)
                }
            }
        }
    </script>
</body>

</html>
标签：canvas,const,image,ctx,刮刮卡,height,event
来源： https://www.cnblogs.com/letgofishing/p/15615627.html