Allow PositionStack to specify the directions on negatives and positives seperately

[yutannihilation]

Context: I need this to finish #3529 (comment)

PositionStack allows to flip the stacking direction by reverse parameter, but it forces the data on the positive side and on the negative side have the same direction.

ggplot2/R/position-stack.r

Lines 191 to 204 in 528a374

	if (any(negative)) {
	neg <- collide(neg, NULL, "position_stack", pos_stack,
	vjust = params$vjust,
	fill = params$fill,
	reverse = params$reverse
	)
	}
	if (any(!negative)) {
	pos <- collide(pos, NULL, "position_stack", pos_stack,
	vjust = params$vjust,
	fill = params$fill,
	reverse = params$reverse
	)
	}

However, it's not a rare case we want to stack them in the opposite direction (i.e. reverse the direction only on the negative side) to draw data properly. geom_area() is the very example for this. I wonder if PositionStack can accept these.

For the interface, I don't come up with a nice idea yet, but it would be something like:

geom_area(
  position = position_stack(reverse = c(positive = FALSE, positive = TRUE))
)

or

geom_area(
  position = position_stack(reverse = TRUE, mirrored = TRUE)
)

[yutannihilation]

Superseded by #3673

[lock]

This old issue has been automatically locked. If you believe you have found a related problem, please file a new issue (with reprex) and link to this issue. https://reprex.tidyverse.org/