Feature request: Let `Facet` act with the `panel_params`

[Yunuuuu]

I've implemented the feature discussed in #6262 and successfully created this facet. However, it requires a workaround using the following ggplot_add method to allow Facet to interact with panel_params:

#' @importFrom ggplot2 ggplot_add ggproto ggproto_parent
#' @export
ggplot_add.ggalign_facet_sector <- function(object, plot, object_name) {
    ParentLayout <- plot$layout
    plot$layout <- ggproto(
        NULL, ParentLayout,
        setup_panel_params = function(self) {
            ggproto_parent(ParentLayout, self)$setup_panel_params()
            if (!is.null(self$facet$setup_panel_params)) {
                self$panel_params <- self$facet$setup_panel_params(
                    self$coord, self$panel_params
                )
            }
            invisible()
        }
    )
    NextMethod()
}

If possible, I’d like to contribute this facet to the ggplot2 repository. Regarding the issue raised in #6262, I realized we can introduce a new theme element, sector.spacing, similar to panel.spacing, but defined in terms of theta rather than absolute units.

[teunbrand]

Giving facets access to panel parameters sounds like an infrastructure question. Can you go a little bit more into the specifics of during what facet method you would need access to the panel parameters (and for context: to do what exactly)?

If possible, I’d like to contribute this facet to the ggplot2 repository.

Nice job on getting this to work so far! I like to re-iterate that this is a good fit for an extension package. ggplot2 isn't looking to add any non-core features and instead focusses on the basics, infrastructure and improvement to systems. The extension system is built with the express purpose that people have the freedom to implement anything that may fall outside what ggplot2 considers core features.

[Yunuuuu]

Apologies for the delay—I’m currently working on my graduation design, so my responses on GitHub may be a bit delayed.

Thanks for the clarification! My goal is to introduce a set_panel_params method within the FACET object, enabling it to modify the panel parameters for each facet panel. This would provide greater flexibility in handling panel-specific adjustments within facets.

My implementation is available here: https://github.com/Yunuuuu/ggalign/blob/main/R/ggplot-facet-sector.R#L98 (please see lines 98-150 for what I actually do in the set_panel_params method). I’d love to hear your thoughts on whether this aligns with ggplot2’s infrastructure principles and if there are any potential concerns or improvements you’d suggest.