WIP: set common scale parameters outside of the scale function

NAMESPACE

@@ -60,6 +60,7 @@ S3method(ggplot_add,default)
 S3method(ggplot_add,guides)
 S3method(ggplot_add,labels)
 S3method(ggplot_add,list)
+S3method(ggplot_add,scales_params)
 S3method(ggplot_add,theme)
 S3method(ggplot_add,uneval)
 S3method(ggplot_build,ggplot)

R/plot-build.r

@@ -35,6 +35,10 @@ ggplot_build.ggplot <- function(plot) {
   layer_data <- lapply(layers, function(y) y$layer_data(plot$data))
 
   scales <- plot$scales
+  # Make sure all scales are provided with any parameters that were separately
+  # provided. Note: this excludes missing but required scales, which don't yet
+  # exist at this time.
+  scales$update_scales_params()
   # Apply function to layer and matching data
   by_layer <- function(f) {
     out <- vector("list", length(data))

R/plot-construction.r

@@ -115,6 +115,11 @@ ggplot_add.Scale <- function(object, plot, object_name) {
   plot
 }
 #' @export
+ggplot_add.scales_params <- function(object, plot, object_name) {
+  plot$scales$add_params(object)
+  plot
+}
+#' @export
 ggplot_add.labels <- function(object, plot, object_name) {
   update_labels(plot, object)
 }

R/scale-.r

@@ -341,6 +341,9 @@ binned_scale <- function(aesthetics, scale_name, palette, name = waiver(),
 #'   (for non-position scales) or when the `Layout` calculates the x and y labels
 #'   (position scales).
 #'
+#' - `update_params()` Method to feed scale parameters into scale object at the end of
+#'   plot construction. For ggplot2 internal use only.
+#'
 #' These methods are only valid for position (x and y) scales:
 #'
 #' - `dimension()` For continuous scales, the dimension is the same concept as the limits.
@@ -388,6 +391,8 @@ Scale <- ggproto("Scale", NULL,
   guide = "legend",
   position = "left",
 
+  update_params = function(self, params) {
+  },
 
   is_discrete = function() {
     abort("Not implemented")
@@ -548,6 +553,13 @@ ScaleContinuous <- ggproto("ScaleContinuous", Scale,
   n.breaks = NULL,
   trans = identity_trans(),
 
+  update_params = function(self, params) {
+    self$name <- params$name %||% self$name
+    self$breaks <- params$breaks %||% self$breaks
+    self$labels <- params$labels %||% self$labels
+    self$expand <- params$expand %||% self$expand
+  },
+
   is_discrete = function() FALSE,
 
   train = function(self, x) {

R/scales-.r

@@ -8,6 +8,7 @@ scales_list <- function() {
 
 ScalesList <- ggproto("ScalesList", NULL,
   scales = NULL,
+  scales_params = list(),
 
   find = function(self, aesthetic) {
     vapply(self$scales, function(x) any(aesthetic %in% x$aesthetics), logical(1))
@@ -36,6 +37,33 @@ ScalesList <- ggproto("ScalesList", NULL,
     self$scales <- c(self$scales[!prev_aes], list(scale))
   },
 
+  # Save parameters for a scale, to be applied later
+  # via `update_scales_params()`. The `params` object
+  # should be created with `scales_params()`.
+  add_params = function(self, params) {
+    aesthetic <- params$aesthetic
+    self$scales_params[[aesthetic]] <-
+      defaults(params$params, self$scales_params[[aesthetic]])
+  },
+
+  # update the parameters for all scales currently stored
+  update_scales_params = function(self) {
+    for (scale in self$scales) {
+      self$update_params_for_scale(scale)
+    }
+  },
+
+  # update the parameters for one specific scale object
+  update_params_for_scale = function(self, scale) {
+    # get a list of all the params objects that are possibly relevant
+    params_list <- self$scales_params[scale$aesthetics]
+    # update the scale with each params object
+    lapply(params_list, function(x) {
+      if (!is.null(x)) scale$update_params(x)
+    })
+    invisible()
+  },
+
   n = function(self) {
     length(self$scales)
   },
@@ -100,7 +128,12 @@ scales_add_defaults <- function(scales, data, aesthetics, env) {
   datacols <- compact(datacols)
 
   for (aes in names(datacols)) {
-    scales$add(find_scale(aes, datacols[[aes]], env))
+    # find the appropriate scale object
+    scale <- find_scale(aes, datacols[[aes]], env)
+    # make sure it has the latest available parameters
+    scales$update_params_for_scale(scale)
+    # add to scales list
+    scales$add(scale)
   }
 
 }
@@ -115,9 +148,27 @@ scales_add_missing <- function(plot, aesthetics, env) {
   for (aes in aesthetics) {
     scale_name <- paste("scale", aes, "continuous", sep = "_")
 
-    scale_f <- find_global(scale_name, env, mode = "function")
-    plot$scales$add(scale_f())
+    # find the appropriate scale object
+    scale_fun <- find_global(scale_name, env, mode = "function")
+    scale <- scale_fun()
+    # make sure it has the latest available parameters
+    scales$update_params_for_scale(scale)
+    # add to scales list
+    plot$scales$add(scale)
   }
 }
 
 
+# create a data structure to store parameters to be added to scales later on
+# @param aesthetic A single aesthetic, *not* a vector of aesthetics.
+# @param ... Parameters to be provided to the scale.
+scales_params <- function(aesthetic, ...) {
+  structure(
+    list(
+      aesthetic = aesthetic,
+      params = list(...)
+    ),
+    class = "scales_params"
+  )
+}
+