Using translate3d and scale for transformations

Question

I wanted to make a div that follows the cursor and simultaneously grows/shrinks as an animation.
I changed the position of the div using top and left but the animation is sometimes a bit choppy.

I wanted to use translate3d to make the animations smooth, but I'm struggling to combine translate3d with scale

const moveCursor = event => {
    const cursorWidth = cursor.offsetWidth / 2;
    cursor.style.left = event.pageX - cursorWidth + "px";
    cursor.style.top = event.pageY - cursorWidth + "px";
};

I wanted to modify this function to use translate3d instead of top and left and keep the existing scale transformation values from the animation

I came up with this, but it isn't working

const moveCursor = event => {
    const cursorWidth = cursor.offsetWidth / 2;
    const xCoordinate = event.pageX - cursorWidth + "px";
    const yCoordinate = event.pageY - cursorWidth + "px";

    const matrix = window.getComputedStyle(cursor).transform;
    const scalingFactor = parseFloat(matrix.split(",")[3]);

    cursor.style.transform = `translate3d(${xCoordinate},${yCoordinate},0px) scale(${scalingFactor})`
};

Where am I going wrong?

const cursor = document.getElementById("cursor");
const moveCursor = event => {
  const cursorWidth = cursor.offsetWidth / 2;
  cursor.style.left = event.pageX - cursorWidth + "px";
  cursor.style.top = event.pageY - cursorWidth + "px";
};
document.addEventListener("mousemove", moveCursor);

#background {
  position: relative;
  height: 100vh;
  width: 100vw;
  overflow: hidden;
  background-color: #0e0e0e;
  color: ivory;
  font-size: 3rem;
  text-align: center;
}

#cursor {
  width: 15rem;
  height: 15rem;
  will-change: transform;
  background: ivory;
  position: absolute;
  mix-blend-mode: difference;
  border-radius: 50%;
  animation: grow-shrink 4s infinite alternate;
}

@keyframes grow-shrink {
  0% {
    transform: scale(1.2);
  }
  25% {
    transform: scale(0.8);
  }
  50% {
    transform: scale(1.2);
  }
  75% {
    transform: scale(0.8);
  }
  100% {
    transform: scale(1);
  }
}

<div id="background">
  Lorem Ipsum
  <div id="cursor"></div>
</div>

Kaiido · Accepted Answer · 2020-07-27T04:39:00.820

The animation will override the values you set with elem.style.
To circumvent this you could add a wrapper element only for translation and keep the scale animation on the wrapped element, or you should have been able to use css-variables to update the translation values in the animation, except that Chrome doesn't update the animation for I don't know what reasons:

This snippet will only work in Firefox

const cursor = document.getElementById("cursor");
const moveCursor = event => {
  const cursorWidth = cursor.offsetWidth / 2;
  cursor.style.setProperty( '--translate-x', event.pageX - cursorWidth + "px" );
  cursor.style.setProperty( '--translate-y', event.pageY - cursorWidth + "px" );
;}
document.addEventListener("mousemove", moveCursor);

#background {
  position: relative;
  height: 100vh;
  width: 100vw;
  overflow: hidden;
  background-color: #0e0e0e;
  color: ivory;
  font-size: 3rem;
  text-align: center;
}

#cursor {
  width: 15rem;
  height: 15rem;
  will-change: transform;
  background: ivory;
  position: absolute;
  mix-blend-mode: difference;
  border-radius: 50%;
  animation: grow-shrink 4s infinite alternate;
  --translate-x: 0px;
  --translate-y: 0px;
  --translate: translate( var(--translate-x), var(--translate-y) );
}

@keyframes grow-shrink {
  0% {
    transform: var(--translate) scale(1.2);
  }
  25% {
    transform: var(--translate) scale(0.8);
  }
  50% {
    transform: var(--translate) scale(1.2);
  }
  75% {
    transform: var(--translate) scale(0.8);
  }
  100% {
    transform: var(--translate) scale(1);
  }
}

<div id="background">
  Lorem Ipsum
  <div id="cursor"></div>
</div>

So this leaves us with the wrapper solution:

const cursor = document.getElementById("trans-wrapper");
const moveCursor = event => {
  const cursorWidth = cursor.offsetWidth / 2;
  cursor.style.left = event.pageX - cursorWidth + "px";
  cursor.style.top = event.pageY - cursorWidth + "px";
};
document.addEventListener("mousemove", moveCursor);

#background {
  position: relative;
  height: 100vh;
  width: 100vw;
  overflow: hidden;
  background-color: #0e0e0e;
  color: ivory;
  font-size: 3rem;
  text-align: center;
}

#cursor {
  width: 15rem;
  height: 15rem;
  will-change: transform;
  background: ivory;
  border-radius: 50%;
  animation: grow-shrink 4s infinite alternate;
}
#trans-wrapper {
  width: 15rem;
  height: 15rem;
  will-change: transform;
  position: absolute;
  mix-blend-mode: difference;  
}


@keyframes grow-shrink {
  0% {
    transform: scale(1.2);
  }
  25% {
    transform: scale(0.8);
  }
  50% {
    transform: scale(1.2);
  }
  75% {
    transform: scale(0.8);
  }
  100% {
    transform: scale(1);
  }
}

<div id="background">
  Lorem Ipsum
  <div id="trans-wrapper">
    <div id="cursor"></div>
  </div>
</div>

Using translate3d and scale for transformations

1 Answers1

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