FEAT: Let geoms define scale parameters and pass those to the scales

R/geom-.r

@@ -202,8 +202,20 @@ Geom <- ggproto("Geom",
   },
 
   # Should the geom rename size to linewidth?
-  rename_size = FALSE
-
+  rename_size = FALSE,
+  # Parameters to pass to scale$map() for each aesthetic:
+  # This can be either a named list (names are aesthetics, values are lists of parameters)
+  # or a function that takes a list of geom parameters as input and returns the list.
+  # The scale_params can be used to tell the scale map function a mapping method.
+  #   e.g. scale_params = list(fill = list(mapping_method = "raw"))
+  # See the map method for ScaleContinuous in R/scale-.r for further details.
+  #
+  # The scale_params will be used to tell the scale map function the expected colour
+  # format, in case the geom prefers native colours (because it uses nativeRaster objects)
+  # instead of the default character vector:
+  #   e.g. scale_params = list(fill = list("color_fmt" = "character")) # "#00FF00"
+  #   e.g. scale_params = list(fill = list("color_fmt" = "native"))    # from nativeRaster
+  scale_params = list()
 )
 
 

R/layer.r

@@ -391,6 +391,14 @@ Layer <- ggproto("Layer", NULL,
     self$geom$setup_data(data, self$computed_geom_params)
   },
 
+  get_scale_params = function(self) {
+    if (is.function(self$geom$scale_params)) {
+      self$geom$scale_params(params = self$computed_geom_params)
+    } else {
+      self$geom$scale_params
+    }
+  },
+
   compute_position = function(self, data, layout) {
     if (empty(data)) return(data_frame0())
 

R/plot-build.r

@@ -88,7 +88,8 @@ ggplot_build.ggplot <- function(plot) {
   npscales <- scales$non_position_scales()
   if (npscales$n() > 0) {
     lapply(data, scales_train_df, scales = npscales)
-    data <- lapply(data, scales_map_df, scales = npscales)
+    scale_params <- by_layer(function(l, d) l$get_scale_params(), layers, data, "getting scale_params")
+    data <- mapply(scales_map_df, df = data, scale_params = scale_params, MoreArgs = list(scales = npscales), SIMPLIFY = FALSE)
   }
 
   # Fill in defaults etc.