万圣节动画-canvas像素点
万圣节到了,写一个小例子了解一下canvas画图方法,canvas可以实现一些有趣的效果,动画实现。以一个简单的页面实现了解一下基础的画图方法。
原文链接
canvas可以实现一些有趣的效果,动画实现。以一个简单的页面实现了解一下基础的画图方法。
效果
预备知识
let canvas = document.getElementById('canvas'); let context = canvas.getContext('2d');
## 开始路径
context.beginPath();
beginPath()方法在画布上开始一条绘制路径,或重置当前的路径。
移动路径
context.moveTo();
moveTo()方法把路径移动到画布中指定点,不创建线条。
添加线条
context.lineTo();
lineTo()方法添加一个新点,在画布中创建该点到指定点的线条。
画图drawImage
context.drawImage(image,x,y);
drawImage()方法可以在画布上绘制图像、画布或视频,也可以绘制图像的某些部分,增加/减少图像的尺寸。
获取像素数据
context.getImageData(x,y,width,height);
getImageData()方法可以获取画布imageData对象,该对象指定了矩形的像素数据。
在imageData对象中每个像素都存在rgba值,以数组形式存储在data属性中。
放回像素数据
context.putImageData(imageData,x,y);
putImageData()方法将获取的图像数据放回到画布上。
实现
html
<canvas id="canvas"></canvas> <button id="click" class="switch">Click</button>
## css
html, body, canvas { width: 100%; height: 100%; margin: 0; } .switch { position: absolute; top: 70%; right: 10%; width: 50px; height: 50px; border-radius: 50px; outline: none; cursor: pointer; animation: switch-animate alternate infinite ease 1s 0s; } @keyframes switch-animate { from { box-shadow: 0 0 30px #ece9c5; } to { box-shadow: 0 0 100px #eae5a7; } }
## js
(function () { class Halloween { constructor(id) { this.canvas = document.getElementById(id); this.ctx = this.canvas.getContext('2d'); this.w = this.canvas.width; this.h = this.canvas.height; this.data = []; } //初始画布 initDraw(img) { this.w = this.canvas.width = img.width; this.h = this.canvas.height = img.height; this.ctx.drawImage(img, 0, 0); this.data = this.ctx.getImageData(0, 0, this.w, this.h); } //显示文字 drawText() { this.ctx.font = '60px Verdana'; this.ctx.fillStyle = '#ffffff'; this.ctx.fillText('万圣节快乐', 350, 280); } //闪电 lightning() { let ctx = this.ctx; ctx.strokeStyle = '#fff'; ctx.lineWidth = 2; ctx.beginPath(); ctx.moveTo(800, 10); ctx.lineTo(600, 100); ctx.lineTo(500, 200); ctx.stroke(); ctx.beginPath(); ctx.moveTo(600, 100); ctx.lineTo(650, 170); ctx.stroke() } //打雷 thunder() { let timer = Math.floor(800 * Math.random()); this.reverse(); this.lightning(); this.drawText(); setTimeout(() => { this.reset(); }, timer); } //反转画布 reverse() { let imgData = this.ctx.getImageData(0, 0, this.w, this.h); for (var i = 0, len = imgData.data.length; i < len; i += 4) { imgData.data[i] = 255 - imgData.data[i]; imgData.data[i + 1] = 255 - imgData.data[i + 1]; imgData.data[i + 2] = 255 - imgData.data[i + 2]; imgData.data[i + 3] = 255; } this.ctx.putImageData(imgData, 0, 0); } //重置画布 reset() { this.ctx.putImageData(this.data, 0, 0); } }
let halloween = new Halloween('canvas'); let canvas = document.getElementById('canvas'); let ctx = canvas.getContext('2d'); let img = new Image(); img.src = '/images/halloween.png'; img.onload = () => { halloween.initDraw(img); } document.getElementById('click').onclick = () => { halloween.thunder(); } })();
# 总结
万圣节快乐?
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