Wrong image width calculation in ImageVariantsUtility.php

[stephankellermayr]

Bug Report

Prerequisites

• Can you reproduce the problem on TYPO3 v11.5 LTS
• Can you reproduce the problem on TYPO3 v12.4 LTS
• Did you perform a cursory search
  to see if your bug or enhancement is already reported?

Description

Once again, a brilliant mathematician has pulled off a stroke of genius and caused the widths of the images not to be calculated correctly:

For example, the CSS states:

.textmedia-item, .textpic-item {
	width: calc(50% -(40px / 2));
}

Which, for example, leads to an image size of 620px with a container width of 1280px. logical, because $1280 * 0.5 - 40 / 2 = 620$

PHP produces the same result in this case, as the gutters are removed first and then the multiplier is applied.
Mathematically a different way, but in this case the same result: $(1280 - 40) * 0.5 = 620$

However, if a different multiplier is used, such as 25% instead of 50%, the situation is unfortunately different.
CSS calculates: $1280 * 0.25 - 40 / 2 = 300$
And PHP calculates: $(1280 - 40) * 0.25 = 310$

Ergo:
If you want to reflect the calculation of image/text widths used in SCSS in PHP code, you would first have to apply the multiplier and then subtract half the gutter.