在任何非白色背景上将文本颜色更改为白色 [英] Change text color to white on any non-white background

问题描述

使用mix-blend-mode: difference可以将背景颜色为黑色时将文本颜色更改为白色.将鼠标移到文本上可以查看效果:

Changing the text color to white when the background color is black works great using mix-blend-mode: difference. Move the mouse to the text to see the effect:

const blackBox = document.querySelector(".black-box");
window.addEventListener('mousemove', function(event) {
  blackBox.style.left = `${event.pageX - 50}px`;
  blackBox.style.top = `${event.pageY - 50}px`;
});

.wrapper {
  background-color: white;
}
h1 {
  position: relative;
  z-index: 2;
  color: white;
  mix-blend-mode: difference;
}

.black-box {
  width: 100px;
  height: 100px;
  position: absolute;
  z-index: 1;
  background-color: black;
}

<div class="wrapper">
  <h1>Lorem Ipsum</h1>
</div>
<div class="black-box"></div>

如果背景不是黑色，则不会产生白色文本，这是可以理解的:

This understandably doesn't result in white text if the background is anything other than black:

const box = document.querySelector(".box");
window.addEventListener('mousemove', function(event) {
  box.style.left = `${event.pageX - 50}px`;
  box.style.top = `${event.pageY - 50}px`;
});

.wrapper {
  background-color: white;
}
h1 {
  position: relative;
  z-index: 2;
  color: white;
  mix-blend-mode: difference;
}

.box {
  width: 100px;
  height: 100px;
  position: absolute;
  z-index: 1;
  background-image: url("https://placekitten.com/100/100")
}

<div class="wrapper">
  <h1>Lorem Ipsum</h1>
</div>
<div class="box"></div>

有什么方法可以使背景一旦与白色不同，文本就会从黑色变为白色?

Is there any way to make it so the text changes color from black to white as soon as the background differs from white?

推荐答案

这是一个依靠背景颜色而不是mix-blend-mode的想法.诀窍是要使用与图像相同尺寸的渐变，并以相同的方式模拟混合模式:

Here is an idea that rely on background coloration and not mix-blend-mode. The trick is to have a gradient with the same dimension as the image that you move the same way to simulate the blend mode:

const box = document.querySelector(".box");
const h1 = document.querySelector("h1");
window.addEventListener('mousemove', function(event) {
  box.style.left = `${event.pageX - 50}px`;
  box.style.top = `${event.pageY - 50}px`;
  
  h1.style.backgroundPosition = `${event.pageX - 50}px ${event.pageY - 50}px`;
});

.wrapper {
  background-color: white;
}
h1 {
  position: relative;
  z-index: 2;
  color: white;
  background: 
    /*gradient                   position   /    size  */
    linear-gradient(#fff,#fff) -100px -100px/100px 100px fixed no-repeat,
    #000;
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  color: transparent;
}

.box {
  width: 100px;
  height: 100px;
  position: absolute;
  z-index: 1;
  background-image: url("https://placekitten.com/100/100")
}

<div class="wrapper">
  <h1>Lorem Ipsum</h1>
</div>
<div class="box"></div>

我已经考虑过background-attachment:fixed相对于视口放置渐变，因为您的元素是position:absolute，没有祖先放置，因此它也相对于视口放置.

I have considered background-attachment:fixed to place the gradient relatively to the viewport since your element is position:absolute with no ancestor positioned so it's also positioned relatively to the viewport.

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