Recalculate transform origin on a scaled element

Question

I have an element which has to be scaled from 100px from the left while already having a scale of 0.5. When transforming the origin it is on 50px on the left side and scaling from the wrong side of the line.

When scaling the element I want it to scale from the purple line. Without using the left CSS property.

I tried to use this formula but it was slightly off:

x + (x * scale)

* {
  margin: 0;
  padding: 0;
}

.box {
  position: relative;
  width: 100px;
  height: 100px;
  margin-top: -10px;
}

.example-initial {
  background: blue;
  transform: scale(0.2);
  transform-origin: 100px 0px;
}

.example-wrong {
  background: green;
  transform: scale(0.5);
  transform-origin: 100px 0px;
}

.example-right {
  background: red;
  transform: scale(0.5);
  transform-origin: 200px 0px;
}

.transform-origin-line-example {
  position: absolute;
  left: 100px;
  width: 1px;
  height: 200px;
  background: purple;
  top: 0;
}

<div class="example-initial box"></div>

<div class="example-wrong box"></div>

<div class="example-right box"></div>

<div class="transform-origin-line-example"></div>

Answer 1

The formula you're looking for is:

(x * (1 / (1 - 0.1));

x is the left position.
1 is the full scale.
0.1 is the used scale.

* {
  margin: 0;
  padding: 0;
}

.box {
  position: relative;
  background: red;
  width: 100px;
  height: 100px;
  transform: scale(0.1);
  transform-origin: calc(100px * (1 / 0.9)) 0px;
} 

.example-box {
  position: relative;
  background: blue;
  width: 100px;
  height: 100px;
  transform: scale(0.5);
  transform-origin: calc(100px * (1 / 0.5))  0px;
}

.transform-origin-line-example {
  position: absolute;
  left: 100px;
  width: 1px;
  height: 200px;
  background: green;
  top: 0;
}

<div class="box"></div>

<div class="example-box"></div>

<div class="transform-origin-line-example"></div>