javascript Canvas 实现打字机效果
js + canvas 应用案例
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<!DOCTYPE html>
<html lang="zh-cn">
<head>
<meta charset="utf-8">
<title>typewritter</title>
<style type="text/css">
body {
display: flex;
flex-direction: column;
align-items: center;
}
canvas#myCanvas
{
width:500px;
height:300px;
background:#eeeeee;
border-radius: 5px;
}
</style>
</head>
<body>
打字机效果
<div id="canvasWrapper">
<canvas id="myCanvas"></canvas>
</div>
<script type="text/javascript">
function TypeWritter(canvasID,config={}) {
this.canvas = document.querySelector(canvasID);
this.canvas.setAttribute('width',this.canvas.offsetWidth+'px');
this.canvas.setAttribute('height',this.canvas.offsetHeight+'px');
this.ctx = this.canvas.getContext("2d");
this.CANVAS_CONFIG = Object.assign({
paddingX : 20, // 画布垂直边距
paddingY : 10, // 画布水平边距
},config);
this.FONT_CONFIG = {
fillStyle:'#000000',
textBaseline:'top',// 默认为alphabetic，为便于计算字符位置做了修改
font:'20px sens-serif'
};
this.V_SPACING = parseInt(parseInt(this.FONT_CONFIG.font)*0.5); // 字符垂直间距
this.H_SPACING = parseInt(parseInt(this.FONT_CONFIG.font)*0.2); // 字符水平间距
this.resetCursor();
}
TypeWritter.prototype = {
constructor:TypeWritter,
randomColor:()=> '#' + Math.floor(Math.random()*16777215).toString(16).padStart(6, '0'),
clear:function () {
this.ctx.clearRect(0,0,this.canvas.offsetWidth,this.canvas.offsetHeight);
this.resetCursor();
return this;
},
resetCursor:function(x=undefined,y=undefined) {
const _x = (typeof x == 'undefined')?this.CANVAS_CONFIG.paddingX:x;
const _y = (typeof y == 'undefined')?this.CANVAS_CONFIG.paddingY:y;
this.cursor_pos = {x:_x,y:_y};
return this;
},
print_char:async function (char,x=undefined,y=undefined,font_config={}) {
Object.assign(this.ctx,this.FONT_CONFIG,font_config);
// ctx.beginPath(); // beginPath 用于 draw 相关的图形操作对text无效
textMetrics = this.ctx.measureText(char);
// 未传入光标位置时，使用上次打印输出之后的位置
x = (typeof x == 'undefined')?this.cursor_pos.x:x;
y = (typeof y == 'undefined')?this.cursor_pos.y:y;
const bIsLineBreak = ['\n','\r'].includes(char);// 文字中有换行标记
//水平方向溢出
const bIsHOverflow = (x + textMetrics.width)>(this.canvas.offsetWidth-2*this.CANVAS_CONFIG.paddingX);
if (bIsLineBreak || bIsHOverflow) {
this.cursor_pos.x = this.CANVAS_CONFIG.paddingX;
this.cursor_pos.y = y + parseInt(this.ctx.font) + this.V_SPACING;
}
if (bIsLineBreak) return this;
console.log(`当前字符 ${char}, 位于 x=${x},y=${y}`); //计算位置
this.ctx.fillText(char,this.cursor_pos.x,this.cursor_pos.y);
Object.assign(this.cursor_pos,{
x:this.cursor_pos.x + textMetrics.width+this.H_SPACING,
y:this.cursor_pos.y
}); // 光标位置
// ctx.lineTo(col*25,row*25);
// ctx.stroke();
return this;
},
write:async function(string,interval=100) {
for(let char of string)
await this.print_char(char,undefined,undefined,{
fillStyle:this.randomColor()
}).then(()=>this.sleep(interval))
return this;
},
sleep:function (interval=0) { //interval millionseconds
let animate_id = null;
interval = Number.isNaN(Number(interval))?1000:Number(interval);
return new Promise((resolve,reject) => {
const _sleep = (_starttime = 0) => {
if((new Date().getTime()-_starttime)<interval)
animate_id = window.requestAnimationFrame(_sleep.bind(null,_starttime)); // 递归
else {
window.cancelAnimationFrame(animate_id);
resolve(this);
}
}
window.requestAnimationFrame(_sleep.bind(null,new Date().getTime()))
});
}
}
window.onload = function() {
let tw = new TypeWritter("#myCanvas");
const poem = `
青天有月来几时，我今停杯一问之。
人攀明月不可得，月行却与人相随。
皎如飞镜临丹阙，绿烟灭尽清辉发。
但见宵从海上来，宁知晓向云间没。
白兔捣药秋复春，嫦娥孤栖与谁邻。
今人不见古时月，今月曾经照古人。
古人今人若流水，共看明月皆如此。
唯愿当歌对酒时，月光长照金樽里。`; //先显示
tw.write(poem)
.then(writer=>writer.sleep(5000))
.then(writer=>writer.clear())
.then(writer=>writer.write(poem));
}
</script>
</body>
</html>
本文由作者按照 CC BY 4.0 进行授权