首页 前端知识 【canvas】前端创造的图片粒子动画效果:HTML5 Canvas 技术详解

【canvas】前端创造的图片粒子动画效果:HTML5 Canvas 技术详解

2024-05-07 13:05:24 前端知识 前端哥 280 424 我要收藏

前端创造的图片粒子动画效果:HTML5 Canvas 技术详解

我们将深入探讨如何通过 HTML5 的 Canvas 功能,将上传的图片转换成引人入胜的粒子动画效果。这种效果将图片分解成小粒子,并在用户与它们交互时产生动态变化。我们将分步骤详细解析代码,让你能够理解每一行代码的作用,并自己实现这一效果。
在这里插入图片描述

环境准备

首先,你需要一个简单的 HTML 元素和一些样式设置:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Particle Image Animation from Uploaded Image</title>
    <style>
        body {
            display: flex;
            justify-content: center;
            align-items: center;
            height: 100vh;
            margin: 0;
            background-color: #f0f0f0;
            overflow: hidden;
        }
        canvas, input {
            display: block;
            margin: auto;
        }
    </style>
</head>
<body>
    <input type="file" id="upload" accept="image/*">
    <canvas id="canvas" hidden></canvas>
</body>
</html>

这段 HTML 设置了一个文件输入控件供用户上传图片,以及一个 Canvas 元素用于渲染动画效果。样式使页面内容居中显示,并将背景设置为浅灰色。

JavaScript 部分

JavaScript 脚本是这个效果的核心,下面我们逐一解析每个部分的功能。

1. 初始化和载入图片:
const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
let particles = [];
const numOfParticles = 5000;
const uploadInput = document.getElementById('upload');

uploadInput.addEventListener('change', function(event) {
    const file = event.target.files[0];
    if (file && file.type.startsWith('image')) {
        const reader = new FileReader();
        reader.onload = function(e) {
            const maxSize = 500; // 最大尺寸
                        let width = img.width;
                        let height = img.height;
                        let scale = Math.min(maxSize / width, maxSize / height);
                        if (scale < 1) {
                            width *= scale;
                            height *= scale;
                        }
                        canvas.width = width;
                        canvas.height = height;
                        ctx.drawImage(img, 0, 0, width, height);
                        canvas.hidden = false;
                        const imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
                        createParticles(imageData);
                        animate();
            };
        };
        reader.readAsDataURL(file);
    }
});

在这部分代码中,我们首先获取 Canvas 元素并配置基本画布(context)。监听文件输入控件的变化事件,当用户选择一个图片文件时,使用 FileReader 对象读取文件内容,将其转换为 Base64 编码的 URL,然后载入 <img> 元素。图片载入完毕后,把它绘制到 Canvas 上,然后提取图片的像素数据。

2. 创建粒子:
function createParticles(imageData) {
    particles = [];
    const { width, height } = imageData;
    for (let i = 0; i < numOfParticles; i++) {
        const x = Math.random() * width;
        const y = Math.random() * height;
        const color = imageData.data[(~~y * width + ~~x) * 4];
        particles.push(new Particle(x, y, color));
    }
}

这个函数根据图片的像素数据随机生成指定数量的粒子。每个粒子具有位置(x,y)和基于图片某一点的颜色。粒子的初始位置是随机分布的。

3. 定义粒子对象:
function Particle(x, y, color) {
    this.x = x;
    this.originalX = x;
    this.y = y;
    this.originalY = y;
    this.color = `rgba(${color},${color},${color}, 0.5)`;

    this.draw = function() {
        ctx.fillStyle = this.color;
        ctx.fillRect(this.x, this.y, 2, 2);
    };

    this.update = function() {
        let dx = this.originalX - this.x;
        let dy = this.originalY - this.y;
        this.x += dx * 0.1;
        this.y += dy * 0.1;

        this.draw();
    };
}

粒子对象具有 drawupdate 方法。draw 方法用来在 Canvas 上绘制粒子,update 方法则负责更新粒子的位置,使它们逐渐回到原始位置。

4. 动画循环和鼠标交互:
function animate() {
    ctx.clearRect(0, 0, canvas.width, canvas.height);
    particles.forEach(particle => particle.update());
    requestAnimationFrame(animate);
}

animate 函数清空画布并更新所有粒子的位置,然后通过 requestAnimationFrame 递归调用自身以形成动画循环。

完整代码

复制这段代码到一个.html文件,可以直接在浏览器允许该demo,实际操作一番。

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Particle Image Animation from Uploaded Image</title>
    <style>
        body {
            display: flex;
            justify-content: center;
            align-items: center;
            height: 100vh;
            margin: 0;
            background-color: #f0f0f0;
            overflow: hidden;
        }

        canvas,
        input {
            display: block;
            margin: auto;
        }
    </style>
</head>

<body>
    <input type="file" id="upload" accept="image/*">
    <canvas id="canvas" hidden></canvas>
    <script>
        const canvas = document.getElementById('canvas');
        const ctx = canvas.getContext('2d');
        let particles = [];
        const numOfParticles = 5000;
        const uploadInput = document.getElementById('upload');

        uploadInput.addEventListener('change', function (event) {
            const file = event.target.files[0];
            if (file && file.type.startsWith('image')) {
                const reader = new FileReader();
                reader.onload = function (e) {
                    const img = new Image();
                    img.src = e.target.result;
                    img.onload = function () {
                        const maxSize = 500; // 最大尺寸
                        let width = img.width;
                        let height = img.height;
                        let scale = Math.min(maxSize / width, maxSize / height);
                        if (scale < 1) {
                            width *= scale;
                            height *= scale;
                        }
                        canvas.width = width;
                        canvas.height = height;
                        ctx.drawImage(img, 0, 0, width, height);
                        canvas.hidden = false;
                        const imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
                        createParticles(imageData);
                        animate();
                    };
                };
                reader.readAsDataURL(file);
            }
        });

        function createParticles(imageData) {
            particles = [];
            const { width, height } = imageData;
            for (let i = 0; i < numOfParticles; i++) {
                const x = Math.random() * width;
                const y = Math.random() * height;
                const color = imageData.data[(~~y * width + ~~x) * 4];
                particles.push(new Particle(x, y, color));
            }
        }

        function Particle(x, y, color) {
            this.x = x;
            this.originalX = x;
            this.y = y;
            this.originalY = y;
            this.color = `rgba(${color},${color},${color}, 0.5)`;

            this.draw = function () {
                ctx.fillStyle = this.color;
                ctx.fillRect(this.x, this.y, 2, 2);
            };

            this.update = function () {
                let dx = this.originalX - this.x;
                let dy = this.originalY - this.y;
                this.x += dx * 0.1;
                this.y += dy * 0.1;

                this.draw();
            };
        }

        function animate() {
            ctx.clearRect(0, 0, canvas.width, canvas.height);
            particles.forEach(particle => particle.update());
            requestAnimationFrame(animate);
        }

        canvas.addEventListener('mousemove', function (e) {
            const rect = canvas.getBoundingClientRect();
            const mouseX = e.clientX - rect.left;
            const mouseY = e.clientY - rect.top;

            particles.forEach(particle => {
                const dx = mouseX - particle.x;
                const dy = mouseY - particle.y;
                const dist = Math.sqrt(dx * dx + dy * dy);

                if (dist < 50) {
                    const angle = Math.atan2(dy, dx);
                    particle.x -= Math.cos(angle);
                    particle.y -= Math.sin(angle);
                }
            });
        });
    </script>
</body>

</html>
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