文字自适应背景的若干方案
当页面元素为客户自定义上传图片等场景时，系统不能预先知道图片的主色调，进而导致该区域内字体内容视觉不明显。
CSS3 字体阴影或描边
将字体的颜色与字体的描边或者阴影取反色值，达到两种颜色必定能有一种颜色显眼的效果。同理，若非文字元素，可加边框。
- 优点: 效果可控，实现成本低。
- 缺点: 必须增加描边等额外的样式属性，可能与原设计不符。
<!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>
<style>
.bg {
width: 600px;
height: 300px;
display: table-cell;
text-align: center;
vertical-align: middle;
animation-name: bg-change;
animation-duration: 4s;
animation-iteration-count: infinite;
animation-direction: alternate;
}
.text {
display: inline-block;
font-size: 32px;
}
.stroke {
color: #fff;
-webkit-text-stroke: 1px #000;
}
.shadow {
color: #000;
text-shadow: 3px 3px 3px #fff;
}
@keyframes bg-change {
from {
background: #000;
}
to {
background: #fff;
}
}
</style>
</head>
<body>
<div class="bg">
<span class="text">
<span class="stroke"> 我是描边 </span>
<br />
<span class="shadow"> 我是阴影 </span>
</span>
</div>
</body>
</html>
CSS3 背景混色
借助混色模式的反色模式(或其他与场景更契合的模式)，实现动态变化元素的颜色。
- 优点: 效果尚可，实现成本低。
- 缺点: 指适应父节点，效果并不完全可控。
<!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>
<style>
.bg {
width: 600px;
height: 300px;
display: table-cell;
text-align: center;
vertical-align: middle;
animation-name: bg-change;
animation-duration: 4s;
animation-iteration-count: infinite;
animation-direction: alternate;
}
.text {
display: inline-block;
font-size: 32px;
mix-blend-mode: difference;
color: #fff;
}
@keyframes bg-change {
from {
background: #000;
}
to {
background: #fff;
}
}
</style>
</head>
<body>
<div class="bg">
<span class="text"> 我是文字 </span>
</div>
</body>
</html>
Canvas 区域色值控制
获取canvas指定区域的平均色值，计算出反色值赋予目标元素。
- 优点: 效果可控性强。
- 缺点: 必须借助canvas，实现成本高。
<!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>
<style>
#text {
position: absolute;
top: 140px;
left: 200px;
font-size: 32px;
}
</style>
</head>
<body>
<canvas id="c1" width="600" height="300"></canvas>
<div id="text">我是文字.....</div>
<script>
const c1 = document.getElementById("c1");
const text = document.getElementById("text");
const ctx = c1.getContext("2d");
let theme = false;
/**
* ArrayBuffer 转换为rgbData
*/
function genRgbaData(data) {
const perChunkSize = 4;
return Array.from(data).reduce((rgba, item, index) => {
const subIndex = Math.floor(index / perChunkSize);
if (!rgba[subIndex]) {
rgba[subIndex] = [];
}
rgba[subIndex].push(item);
return rgba;
}, []);
}
/**
* 获取区域内的平均色值
*/
function getColorByAvg(imgRgbaData, sizes) {
const avgColor = {
r: 0,
g: 0,
b: 0,
};
imgRgbaData.forEach((rgba) => {
avgColor.r += rgba[0];
avgColor.g += rgba[1];
avgColor.b += rgba[2];
});
const area = sizes.width * sizes.height;
avgColor.r = (avgColor.r / area) | 0;
avgColor.g = (avgColor.g / area) | 0;
avgColor.b = (avgColor.b / area) | 0;
return avgColor;
}
/**
* 反向色值
*/
function getReverseColor(color) {
const reverseColor = {
r: 255 - color.r,
g: 255 - color.g,
b: 255 - color.b,
};
return reverseColor;
}
function drawImage() {
theme = !theme;
const imgSrc = theme ? "./imgs/light.png" : "./imgs/dark.png";
const img = new Image();
img.src = imgSrc;
img.onload = function () {
ctx.drawImage(img, 0, 0, 600, 300);
const starX = 200,
starY = 140,
chunkWidth = 180,
chunkHeight = 40;
const ImageData = ctx.getImageData(
starX,
starY,
chunkWidth,
chunkHeight
);
const rgbData = genRgbaData(ImageData.data);
const colorInfo = getColorByAvg(rgbData, {
width: chunkWidth,
height: chunkHeight,
});
const reverseColor = getReverseColor(colorInfo);
const txtColor = `rgb(${reverseColor.r}, ${reverseColor.g}, ${reverseColor.b})`;
text.style.color = txtColor;
};
const st = setTimeout(() => {
clearTimeout(st);
drawImage();
}, 4000);
}
drawImage();
</script>
</body>
</html>
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