Issue #303 margin adjustment for multi-line labels and titles

[vincentarelbundock]

This change fixes dynamic margins when annotation text is missing (NA, NULL, or empty) and when labels contain multiple lines.

pkgload::load_all()
tinytheme("clean")

set.seed(1)
x <- 1:20
y <- x + rnorm(length(x), sd = 2)

op <- par(mfrow = c(2, 2))
on.exit(par(op), add = TRUE)
on.exit(tinytheme(), add = TRUE)

tinyplot(x, y, main = "xlab = NA", xlab = NA, ylab = "Y")
tinyplot(x, y, main = "xlab present", xlab = "X", ylab = "Y")
tinyplot(x, y,
  main = "Multi-line labels",
  xlab = "X line 1\nX line 2", ylab = "Y line 1\nY line 2")
tinyplot(x, y, main = "Multi-line\nmain title", xlab = "X", ylab = "Y")

Internal changes:

• Added text_line_count() to normalize line counting for labels/subtitles (treat missing text as 0 lines).
• Passed main/sub/xlab/ylab into facet margin logic and adjusted margins by line count (shrink for missing text, expand for multi-line text).
• Used the same line-counting logic for sub in legend layout, so sub = NA no longer reserves extra bottom space.

Testing note:

• Added/updated margin snapshots for missing and multi-line labels (including a 2x2 case).
• Regenerated ridge snapshots because previous renders showed extra empty space at the top; the updated margin logic changed panel placement.

[grantmcdermott]

Super, thanks for taking this on. I kept meaning to, but couldn't find the time...

[vincentarelbundock]

Frankly, I'm not sure I can wrap my head entirely around the margins part of the code. But this seems to be working for the cases I investigated.

So I'd say this is OK for review.

[grantmcdermott]

Left a few quick comments while I had a sec.

I also have a slightly more involved refactor in mind for the core dynamic theme margin adjustment logic. tl;dr Right now, we do things a bit back to front; we assign title space up front and then remove it if it is absent, or increase if it has multiple lines per your PR here. I think we could simplify things for these dnymaic themes, by setting margins that assume no titles a priori and then make (multline) space for them if these titles are present. I'll take a crack at this later today, hopefully.

[grantmcdermott]

I might be misunderstanding, but why calculate in inches (csi) instead of user coords (cxy)?

Where does 0.75 come from? Is it borrowed from one of the (hard-coded) based plot scaling factors? Or, just eye-balling?

[grantmcdermott]

Should we be using get_tpar() here to get theme-specific settings instead of par()?

[grantmcdermott]

Should these par() cases be get_tpar() instead?