Facet: new method setup_panel_params to interact panel_params (#6397)

* `Facet`: new method `setup_panel_params` to interact panel_params

* add dots for future extending

Co-authored-by: Teun van den Brand <[email protected]>

* new bullet

---------

Co-authored-by: Teun van den Brand <[email protected]>

Author: Yunuuuu

Diff for: NEWS.md

@@ -1,5 +1,6 @@
 # ggplot2 (development version)
 
+* Facet gains a new method `setup_panel_params` to interact with the panel_params setted by Coord object (@Yunuuuu, #6397, #6380)
 * `position_fill()` avoids stacking observations of zero (@teunbrand, #6338)
 * New `layer(layout)` argument to interact with facets (@teunbrand, #3062)
 * New `stat_connect()` to connect points via steps or other shapes 

Diff for: R/facet-.R

@@ -46,6 +46,10 @@ NULL
 #' the default behaviour of one or more of the following methods:
 #'
 #'   - `setup_params`:
+#'
+#'   - `setup_panel_params`: modifies the x and y ranges for each panel. This is
+#'     used to allow the `Facet` to interact with the `panel_params`.
+#' 
 #'   - `init_scales`: Given a master scale for x and y, create panel
 #'   specific scales for each panel defined in the layout. The default is to
 #'   simply clone the master scale.
@@ -90,6 +94,7 @@ Facet <- ggproto("Facet", NULL,
   map_data = function(data, layout, params) {
     cli::cli_abort("Not implemented.")
   },
+  setup_panel_params = function(self, panel_params, coord, ...) panel_params,
   init_scales = function(layout, x_scale = NULL, y_scale = NULL, params) {
     scales <- list()
     if (!is.null(x_scale)) {

Diff for: R/layout.R

@@ -210,12 +210,15 @@ Layout <- ggproto("Layout", NULL,
     scales_x <- self$panel_scales_x[self$layout$SCALE_X[index]]
     scales_y <- self$panel_scales_y[self$layout$SCALE_Y[index]]
 
-    self$panel_params <- Map(
+    panel_params <- Map(
       self$coord$setup_panel_params,
       scales_x, scales_y,
       MoreArgs = list(params = self$coord_params)
     )[order] # `[order]` does the repeating
 
+    # Let Facet modify `panel_params` for each panel
+    self$panel_params <- self$facet$setup_panel_params(panel_params, self$coord)
+
     invisible()
   },