canvas高级动画示例

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canvas高级动画示例

演示地址 https://qzruncode.github.io/example/index.html

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style type="text/css">

        canvas {

            border: 1px solid black;

        }

    </style>

</head>

<body>

    <canvas id="canvas" width="500px" height="500px"></canvas>

    <script>

        const canvas = document.getElementById('canvas');

        const ctx = canvas.getContext('2d');

        var cRect = canvas.getBoundingClientRect();

        var raf;

        var running = false;

        var ball = {

            x: 100,

            y: 100,

            vx: 5,

            vy: 2,

            radius: 25,

            color: 'red',

            draw: function () {

                ctx.beginPath();

                ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, true);

                ctx.closePath();

                ctx.fillStyle = this.color;

                ctx.fill();

            }

        };

        function clear() {

            // ctx.clearRect(0, 0, canvas.width, canvas.height);

            // 尾影效果使用下面

            ctx.fillStyle = 'rgba(255, 255, 255, 0.3)';

            ctx.fillRect(0, 0, canvas.width, canvas.height);

        }

        function draw() {

            clear();

            ball.draw();

            // 移动

            ball.x += ball.vx;

            ball.y += ball.vy;

            // 曲线运动

            ball.vy *= .99;

            ball.vy += .25;

            // 边界

            if (ball.y + ball.vy > canvas.height || ball.y + ball.vy < 0) {

                ball.vy = -ball.vy;

            }

            if (ball.x + ball.vx > canvas.width || ball.x + ball.vx < 0) {

                ball.vx = -ball.vx;

            }

            raf = window.requestAnimationFrame(draw);

        }

        canvas.addEventListener('mousemove', function (e) {

            if (!running) {

                clear();

                ball.x = Math.round(e.clientX - cRect.left);

                ball.y = Math.round(e.clientY - cRect.top);

                ball.draw();   // 直接调用draw只会绘制一帧

            }

        });

        canvas.addEventListener('click', function (e) {

            if (!running) {

                raf = window.requestAnimationFrame(draw);

                running = true;

            }

        });

        canvas.addEventListener('mouseout', function (e) {

            window.cancelAnimationFrame(raf);

            running = false;

        });

        ball.draw();

    </script>

</body>

</html>