- 实现思路：用二分法通过context.measureText测试文字宽高，不断计算字体大小
<!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>
</head>
<style>
body {
display: grid;
place-items: center;
}
#demo-div {
display: inline;
background-color: skyblue;
position: relative;
}
#demo-div::after {
position: absolute;
content: '';
width: 0;
height: 50px;
left: 50%;
top: 50%;
transform: translate(-50%, -50%);
border-left: 1px dashed red;
}
#demo-div::before {
position: absolute;
content: '';
width: 200px;
height: 0;
left: 50%;
top: 50%;
transform: translate(-50%, -50%);
border-top: 1px dashed purple;
}
.btn-list {
display: flex;
column-gap: 10px;
margin-bottom: 20px;
}
</style>
<body>
<canvas id="demo-canvas" style="width: 400px; height: 200p;background-color: red;"></canvas>
<div class="btn-list">
<button id="times">Times</button>
<button id="hanab">Hanab</button>
<button id="magnetob">MAGNETOB</button>
<button id="abc">abc</button>
<button id="cn">中</button>
</div>
<div id="demo-div">initial</div>
<script>
const generatePreview = async (
str,
width,
height,
font,
fontUrl,
initFontSize,
) => {
try {
const dpr = window.devicePixelRatio;
const canvas = document.getElementById('demo-canvas');
canvas.width = width * dpr;
canvas.height = height * dpr;
const ctx = canvas.getContext('2d')
ctx.scale(dpr, dpr);
ctx.fillStyle = 'pink';
ctx.fillRect(0, 0, 400, 200);
ctx.fillStyle = 'black';
ctx.font = `normal ${initFontSize}px Times New Roman`;
ctx.textAlign = 'center';
ctx.textBaseline = 'middle';
const getActualHeight = () => {
const { actualBoundingBoxAscent, actualBoundingBoxDescent } = ctx.measureText(str);
return actualBoundingBoxAscent + actualBoundingBoxDescent;
};
const getActualWidth = () => {
const { actualBoundingBoxLeft, actualBoundingBoxRight } = ctx.measureText(str);
return actualBoundingBoxLeft + actualBoundingBoxRight;
};
const dichotomizeCulcalate = (size, max, culcalate) => {
let preResult;
let minSize = size;
let maxSize = size;
do {
preResult = culcalate();
if (preResult > max) {
maxSize = minSize;
minSize = Math.floor(minSize / 2);
} else {
minSize = Math.floor((maxSize - minSize) / 2) + minSize;
}
ctx.font = `normal ${minSize}px ${font}`;
if (maxSize === minSize) break;
} while (preResult !== culcalate());
};
dichotomizeCulcalate(initFontSize, width, getActualWidth);
dichotomizeCulcalate(Number(ctx.font.split('px').shift()), height, getActualHeight);
ctx.fillText(
str,
(width - getActualWidth()) / 2 + ctx.measureText(str).actualBoundingBoxLeft,
(height - getActualHeight()) / 2 + ctx.measureText(str).actualBoundingBoxAscent,
);
return new Promise((resolve, reject) => {
canvas.toBlob((blob) => {
if (blob) {
resolve({
previewBlobUrl: createObjectURL(blob),
previewBlob: blob,
});
} else {
reject(new Error('预览图生成失败'));
}
});
});
} catch (error) {
console.log(error)
}
};
const INIT_FONTSIZE = 500;
const INIT_WIDTH = 400;
const INIT_HEIGHT = 200;
const div = document.getElementById('demo-div')
document.getElementById('times').addEventListener('click', () => {
generatePreview('Times', INIT_WIDTH, INIT_HEIGHT, 'Times', 'Times.ttc', INIT_FONTSIZE)
div.innerText = 'Times'
div.style.fontFamily = 'Times'
})
document.getElementById('hanab').addEventListener('click', () => {
generatePreview('Hanab', INIT_WIDTH, INIT_HEIGHT, 'Hanab', 'Hanab.ttf', INIT_FONTSIZE)
div.innerText = 'Hanab'
div.style.fontFamily = 'Hanab'
})
document.getElementById('magnetob').addEventListener('click', () => {
generatePreview('MAGNETOB', INIT_WIDTH, INIT_HEIGHT, 'MAGNETOB', 'MAGNETOB.ttf', INIT_FONTSIZE)
div.innerText = 'MAGNETOB'
div.style.fontFamily = 'MAGNETOB'
})
document.getElementById('abc').addEventListener('click', () => {
generatePreview('abc', INIT_WIDTH, INIT_HEIGHT, 'MAGNETOB', 'MAGNETOB.ttf', INIT_FONTSIZE)
div.innerText = 'abc'
})
document.getElementById('cn').addEventListener('click', () => {
generatePreview('中', INIT_WIDTH, INIT_HEIGHT, 'MAGNETOB', 'MAGNETOB.ttf', INIT_FONTSIZE)
div.innerText = '中'
})
</script>
</body>
</html>
