Fix back-transformation of ranges in coords, without API cleanup

NEWS.md

@@ -3,8 +3,11 @@
 *   `geom_sf()` now respects `lineend`, `linejoin`, and `linemitre` parameters 
     for lines and polygons (@alistaire47, #2826)
 
+*   `geom_hline()`, `geom_vline()`, and `geom_abline()` now work properly
+    with `coord_trans()` (@clauswilke, #2149, #2812).
+
 *   `benchplot()` now uses tidy evaluation (@dpseidel, #2699).
-    
+
 *   `fortify()` now displays a more informative error message for
     `grouped_df()` objects when dplyr is not installed (@jimhester, #2822).
 

R/coord-.r

@@ -13,14 +13,22 @@
 #'   - `render_bg`: Renders background elements.
 #'   - `render_axis_h`: Renders the horizontal axes.
 #'   - `render_axis_v`: Renders the vertical axes.
-#'   - `range`: Returns the x and y ranges
+#'   - `range(panel_params)`: Extracts the panel range provided
+#'     in `panel_params` (created by `setup_panel_params()`, see below) and
+#'     back-transforms to data coordinates. This back-transformation is needed
+#'     for coords such as `coord_flip()`, `coord_polar()`, `coord_trans()` where
+#'     the range in the transformed coordinates differs from the range in the
+#'     untransformed coordinates.
 #'   - `transform`: Transforms x and y coordinates.
 #'   - `distance`: Calculates distance.
 #'   - `is_linear`: Returns `TRUE` if the coordinate system is
 #'     linear; `FALSE` otherwise.
 #'   - `is_free`: Returns `TRUE` if the coordinate system supports free
-#'     positional scales.
-#'   - `setup_panel_params(data)`:
+#'     positional scales; `FALSE` otherwise.
+#'   - `setup_panel_params(scale_x, scale_y, params)`: Determines the appropriate
+#'     x and y ranges for each panel, and also calculates anything else needed to
+#'     render the panel and axes, such as tick positions and labels for major
+#'     and minor ticks. Returns all this information in a named list.
 #'   - `setup_data(data, params)`: Allows the coordinate system to
 #'     manipulate the plot data. Should return list of data frames.
 #'   - `setup_layout(layout, params)`: Allows the coordinate
@@ -73,8 +81,15 @@ Coord <- ggproto("Coord",
     )
   },
 
+  # transform range given in transformed coordinates
+  # back into range in given in (possibly scale-transformed)
+  # data coordinates
   range = function(panel_params) {
-    return(list(x = panel_params$x.range, y = panel_params$y.range))
+    warning(
+      "range backtransformation not implemented in this coord; plot may be wrong.",
+      call. = FALSE
+      )
+    list(x = panel_params$x.range, y = panel_params$y.range)
   },
 
   setup_panel_params = function(scale_x, scale_y, params = list()) {

R/coord-cartesian-.r

@@ -83,6 +83,10 @@ CoordCartesian <- ggproto("CoordCartesian", Coord,
     dist_euclidean(x, y) / max_dist
   },
 
+  range = function(panel_params) {
+    list(x = panel_params$x.range, y = panel_params$y.range)
+  },
+
   transform = function(data, panel_params) {
     rescale_x <- function(data) rescale(data, from = panel_params$x.range)
     rescale_y <- function(data) rescale(data, from = panel_params$y.range)

R/coord-map.r

@@ -119,6 +119,11 @@ CoordMap <- ggproto("CoordMap", Coord,
     out
   },
 
+  range = function(panel_params) {
+    # range is stored in data coordinates and doesn't have to be back-transformed
+    list(x = panel_params$x.range, y = panel_params$y.range)
+  },
+
   distance = function(x, y, panel_params) {
     max_dist <- dist_central_angle(panel_params$x.range, panel_params$y.range)
     dist_central_angle(x, y) / max_dist

R/coord-transform.r

@@ -119,6 +119,13 @@ CoordTrans <- ggproto("CoordTrans", Coord,
     dist_euclidean(self$trans$x$transform(x), self$trans$y$transform(y)) / max_dist
   },
 
+  range = function(self, panel_params) {
+    list(
+      x = self$trans$x$inverse(panel_params$x.range),
+      y = self$trans$y$inverse(panel_params$y.range)
+    )
+  },
+
   transform = function(self, data, panel_params) {
     trans_x <- function(data) transform_value(self$trans$x, data, panel_params$x.range)
     trans_y <- function(data) transform_value(self$trans$y, data, panel_params$y.range)

R/sf.R

@@ -361,6 +361,10 @@ CoordSf <- ggproto("CoordSf", CoordCartesian,
     )
   },
 
+  range = function(panel_params) {
+    list(x = panel_params$x_range, y = panel_params$y_range)
+  },
+
   # CoordSf enforces a fixed aspect ratio -> axes cannot be changed freely under faceting
   is_free = function() FALSE,