scene: fix scaling of negative coordinates

[zsugabubus]

round() rounds away from zero that can cause unwanted lengthening of
dimensions when sides of box differ in their sign:

scale_length(2, -1, 1.5) == 4 (-1.5 -> -2; 1.5 -> 2)
scale_length(2, 1, 1.5) == 3

[vyivel]

The logic seems right to me.

[emersion]

Hm, maybe we could have a round_up function to make this more explicit?

[ascent12]

I haven't really looked into the issue at all, but would using the other rounding functions like ceil()/floor()/trunc()/rint() work?

[zsugabubus]

Sorry, I have made a big huge mistake here with truncation (towards zero) and adding half (scale = 1, offset < 0 => bleh).

Thinking it over, I would go with ceil(). It has the advantage over round() that moving a line on the screen, does not change its size.

[emersion]

wlroots has migrated to gitlab.freedesktop.org. This pull request has been moved to:

https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/3312