Type argument in scale_[fill/colour]_[continuous/binned] can accept a function

NEWS.md

@@ -2,6 +2,8 @@
 
 * `annotation_raster()` adds support for native rasters. For large rasters,
   native rasters render significantly faster than arrays (@kent37, #3388)
+
+* Default continuous color scales (i.e., the `options()` `ggplot2.continuous.colour` and `ggplot2.continuous.fill`, which inform the `type` argument of `scale_fill_continuous()` and `scale_colour_continuous()`) now accept a function, which allows more control over these default `continuous_scale()`s (@cpsievert, #3827)
 
 # ggplot2 3.3.0
 

R/scale-colour.r

@@ -1,13 +1,15 @@
 #' Continuous and binned colour scales
 #'
 #' Colour scales for continuous data default to the values of the
-#' `ggplot2.continuous.colour` and `ggplot2.continuous.fill` options. If these
-#' options are not present, `"gradient"` will be used. See [options()] for more
-#' information.
+#' `ggplot2.continuous.colour` and `ggplot2.continuous.fill` options. These
+#' [options()] default to `"gradient"` (i.e., [scale_colour_gradient()] and
+#' [scale_fill_gradient()])
 #'
 #' @param ... Additional parameters passed on to the scale type
-#' @param type One of "gradient" (the default) or "viridis" indicating the
-#'   colour scale to use
+#' @param type One of the following:
+#'   * "gradient" (the default)
+#'   * "viridis"
+#'   * A function that returns a continuous colour scale.
 #' @seealso [scale_colour_gradient()], [scale_colour_viridis_c()],
 #'   [scale_colour_steps()], [scale_colour_viridis_b()], [scale_fill_gradient()],
 #'   [scale_fill_viridis_c()], [scale_fill_steps()], and [scale_fill_viridis_b()]
@@ -40,48 +42,60 @@
 #' v + scale_fill_viridis_c()
 scale_colour_continuous <- function(...,
                                     type = getOption("ggplot2.continuous.colour", default = "gradient")) {
-  switch(
-    type,
-    gradient = scale_colour_gradient(...),
-    viridis = scale_colour_viridis_c(...),
+  if (is.function(type)) {
+    type(...)
+  } else if (identical(type, "gradient")) {
+    scale_colour_gradient(...)
+  } else if (identical(type, "viridis")) {
+    scale_colour_viridis_c(...)
+  } else {
     abort("Unknown scale type")
-  )
+  }
 }
 
 #' @rdname scale_colour_continuous
 #' @export
 scale_fill_continuous <- function(...,
                                   type = getOption("ggplot2.continuous.fill", default = "gradient")) {
-  switch(
-    type,
-    gradient = scale_fill_gradient(...),
-    viridis = scale_fill_viridis_c(...),
+  if (is.function(type)) {
+    type(...)
+  } else if (identical(type, "gradient")) {
+    scale_fill_gradient(...)
+  } else if (identical(type, "viridis")) {
+    scale_fill_viridis_c(...)
+  } else {
     abort("Unknown scale type")
-  )
+  }
 }
 
 #' @export
 #' @rdname scale_colour_continuous
 #' @usage NULL
 scale_colour_binned <- function(...,
-                                type = getOption("ggplot2.continuous.colour", default = "gradient")) {
-  switch(
-    type,
-    gradient = scale_colour_steps(...),
-    viridis = scale_colour_viridis_b(...),
+                                type = getOption("ggplot2.binned.colour", default = getOption("ggplot2.continuous.colour", default = "gradient"))) {
+  if (is.function(type)) {
+    type(...)
+  } else if (identical(type, "gradient")) {
+    scale_colour_steps(...)
+  } else if (identical(type, "viridis")) {
+    scale_colour_viridis_b(...)
+  } else {
     abort("Unknown scale type")
-  )
+  }
 }
 
 #' @export
 #' @rdname scale_colour_continuous
 #' @usage NULL
 scale_fill_binned <- function(...,
-                              type = getOption("ggplot2.continuous.colour", default = "gradient")) {
-  switch(
-    type,
-    gradient = scale_fill_steps(...),
-    viridis = scale_fill_viridis_b(...),
+                              type = getOption("ggplot2.binned.fill", default = getOption("ggplot2.continuous.fill", default = "gradient"))) {
+  if (is.function(type)) {
+    type(...)
+  } else if (identical(type, "gradient")) {
+    scale_fill_steps(...)
+  } else if (identical(type, "viridis")) {
+    scale_fill_viridis_b(...)
+  } else {
     abort("Unknown scale type")
-  )
+  }
 }