Background text of attributed string does not work properly on High Sierra when it wraps to multiple lines.

[parro-it]

When a fragment of an attributed string that has background attribute wraps to multiple lines,
the background attribute extends to the end of the last line containing the fragment.

The problem happens only on macOS High Sierra. macOS Sierra is not affected.
The GIF below is taken from the drawtext example:

We discover the problem on libui-node parro-it/libui-node#101

[mischnic]

Could this be a bug in High Sierra because the background is drawn by Core Text and not libui itself?

libui/darwin/attrstr.m

Lines 298 to 309 in cda991b

	// TODO make sure this works properly with line paragraph spacings (after figuring out what that means, of course)
	if (uiprivFUTURE_kCTBackgroundColorAttributeName != NULL) {
	CGColorRef color;
	CFRange range;
	color = mkcolor(r, g, b, a);
	range.location = start;
	range.length = end - start;
	CFAttributedStringSetAttribute(p->mas, range, *uiprivFUTURE_kCTBackgroundColorAttributeName, color);
	CFRelease(color);
	return;
	}

Also, how does it behave on 10.11 and earlier? I guess no background is drawn?

libui/darwin/future.m

Lines 11 to 12 in cda991b

	// added in OS X 10.12; we need 10.8
	CFStringRef *uiprivFUTURE_kCTBackgroundColorAttributeName = NULL;