Minor font rendering glitch

[appgurueu]

Luanti version

Luanti 5.11.0-dev-debug-e5542e5b0 (Linux)
Using LuaJIT 2.1.1713773202
Built by GCC 14.2
Running on Linux/6.9.10 x86_64
BUILD_TYPE=Debug
RUN_IN_PLACE=1
USE_CURL=1
USE_GETTEXT=1
USE_SOUND=1

Operating system and version

Fedora 40

CPU model

AMD Ryzen 5 3500U

GPU model

integrated Radeon™ Vega Mobile Gfx × 8

Active renderer

4.6 / any / SDL

Summary

This is how Intel One Mono renders for me:

Note the glitch on the j:

Steps to reproduce

Set Intel One Mono as monospace font with a size of 20, view e.g. using hypertext.

Discovered while testing #15606 but confirmed independent; the mod recommended for testing there is useful to quickly reproduce this.

[SmallJoker]

It also appears that the bottom pixels are cut off. I would expect at least some aliasing for the y and g letters. Red line for height reference, at a 1 px gap.

[appgurueu]

Yeah, it also seems to be cut off. I wonder whether the following is to blame:

unsigned int FontEngine::getTextHeight(const FontSpec &spec)
{
	gui::IGUIFont *font = getFont(spec);

	return font->getDimension(L"Some unimportant example String").Height;
}

/** get line height for a specific font (including empty room between lines) */
unsigned int FontEngine::getLineHeight(const FontSpec &spec)
{
	gui::IGUIFont *font = getFont(spec);

	return font->getDimension(L"Some unimportant example String").Height
			+ font->getKerning(L'S').Y;
}

Using "some unimportant example string" seems very dubious here.

But what confuses me is that this can't fully explain the glitches. There's more going on here. It looks almost a bit as if some rectangle is intruding upon the glyphs and overwriting the pixels, but I don't see why that would be happening.