Invert colored text related background

Question

I want to invert text color based on the background of the text, like in this image:

.

So I've tried the following code, but it didn't work:

#warp,
#text,
#tri {
  position: absolute;
  top: 0;
  left: 0;
  width: 150px;
  height: 150px;
  z-index: 1;
}

#warp {
  background-color: orange;
}

#text {
  text-align: center;
  z-index: 3;
}

#text h1 {
  margin: 0;
  line-height: 150px;
  mix-blend-mode: difference;
}

#tri {
  background-color: black;
  clip-path: polygon(0 0, 0 100%, 99.8% 150px);
  -webkit-clip-path: polygon(0 0, 0 100%, 99.8% 150px);
  z-index: 2;
}

<div id="warp">
  <div id="text">
    <h1>TEXT</h1>
  </div>
  <div id="tri"></div>
</div>

I found some results about background-image & inverted text, but I don't know how to do it with DIVs.

Answer 1

If you just add the same text to the tri layer, it works:

Edit: In order to allow selecting the text, I've added another transparent layer that wraps all the text as one unit. It does, however, makes updates more repetitive. As a solution, I've added the attached JavaScript code (which isn't necessary).

var text = "TEXT";
var textElements = document.getElementsByTagName("h1");
for (var i=0; i<textElements.length; i++) {
  textElements[i].innerHTML = text;
}

#warp,
#text,
#tri,
#selectable {
  position: absolute;
  top: 0;
  left: 0;
  width: 150px;
  height: 150px;
}

#warp {
  background-color: orange;
}

#text {
  text-align: center;
  z-index: 1;
}

h1 {
  margin: 0;
  line-height: 150px;
  mix-blend-mode: difference;
}

#tri {
  background-color: black;
  clip-path: polygon(0 0, 0 100%, 99.8% 150px);
  -webkit-clip-path: polygon(0 0, 0 100%, 99.8% 150px);
  z-index: 2;
  color: blue;
  text-align: center;
}

#selectable {
  text-align: center;
  z-index: 5;
  color: transparent;
}

<div id="warp">
  <div id="text">
    <h1>TEXT</h1>
  </div>
  <div id="tri">
    <h1>TEXT</h1>
  </div>
  <div id="selectable">
    <h1>TEXT</h1>
  </div>
</div>

Answer 2

You can avoid clip-path by using linear-gradient as background and the mix-blend-mode will work perfectly:

#text {
  width: 150px;
  height: 150px;
  z-index: 1;
}

#text {
  text-align: center;
  background: linear-gradient(to top right, black 50%, orange 51%);
}

#text h1 {
  margin: 0;
  line-height: 150px;
  mix-blend-mode: difference;
  color: #fff;
}

<div id="text">
  <h1>TEXT</h1>
</div>