Expose variable allow_upscale to settings

[discomrade]

In /ext/media/main.php, the variable allow_upscale determines whether an image is allowed to upscale when thumbnailing (e.g. 64x64 sprite gets enlarged to 192x192). Upscaling images smaller than a thumbnail will almost inevitably result in a visible loss of quality and unnecessary filesize increase, and it's reasonable to want this disabled.

Should it be disabled by default and configurable in the setup page?

[shish]

Come to think of it I wonder if there's any reason to upscale ever - I can imagine it being useful to have a minimum thumbnail size eg so that people can click on the thumbnail if somebody uploads a 1x1px image; but then I wonder if that could be done via CSS 🤔

[discomrade]

Come to think of it I wonder if there's any reason to upscale ever

I can't think of any reason to upscale.

but then I wonder if that could be done via CSS

I believe it's best done via HTML/CSS.

The simple ways are to make either the <img> or the <a> have a height and width in CSS. But each has a problem:

• changing the <a> size works, but there's no alt text on hover (shows tags and other information).
• changing the <img> size (and telling it not to stretch) adds the empty space inside the borders, creating a grid of squares.
  

To avoid either downside, we can:

• change the <a> size, and give it title text same as the alt text in the <img>. (/core/basethemelet.php)
• keep the <img> alt text (it's good for SEO).

The CSS for this is:

.shm-image-list .thumb {
	margin-bottom: 11px; /* I don't know why the 8px needs to become 11px when changing to grid/flex */
	min-height: var(--thumb-height);
	min-width: var(--thumb-width);
	display: grid;
	justify-items: center;
	align-items: center;
}