geom_rect() can derive corners from x/width or y/height

NEWS.md

@@ -1,5 +1,8 @@
 # ggplot2 (development version)
 
+* `geom_rect()` can now derive the required corners positions from `x`/`width`
+  or `y`/`height` parameterisation (@teunbrand, #5861).
+
 # ggplot2 3.5.1
 
 This is a small release focusing on fixing regressions from 3.5.0 and 

R/geom-bar.R

@@ -129,6 +129,8 @@ geom_bar <- function(mapping = NULL, data = NULL,
 GeomBar <- ggproto("GeomBar", GeomRect,
   required_aes = c("x", "y"),
 
+  optional_aes = character(),
+
   # These aes columns are created by setup_data(). They need to be listed here so
   # that GeomRect$handle_na() properly removes any bars that fall outside the defined
   # limits, not just those for which x and y are outside the limits

R/geom-rect.R

@@ -31,7 +31,37 @@ GeomRect <- ggproto("GeomRect", Geom,
   default_aes = aes(colour = NA, fill = "grey35", linewidth = 0.5, linetype = 1,
     alpha = NA),
 
-  required_aes = c("xmin", "xmax", "ymin", "ymax"),
+  optional_aes = c("x", "width", "xmin", "xmax", "y", "height", "ymin", "ymax"),
+  non_missing_aes = c("xmin", "xmax", "ymin", "ymax"),
+
+  setup_data = function(self, data, params) {
+    data$xmin <- data$xmin %||% params$xmin
+    data$xmax <- data$xmax %||% params$xmax
+    data$ymin <- data$ymin %||% params$ymin
+    data$ymax <- data$ymax %||% params$ymax
+    if (is.null(data$xmin) || is.null(data$xmax)) {
+      x <- resolve_rect(
+        data[["xmin"]], data[["xmax"]],
+        data[["x"]], data[["width"]] %||% params$width
+      )
+      i <- lengths(x) > 1
+      data[c("xmin", "xmax")[i]] <- x[i]
+    }
+    if (is.null(data$ymin) || is.null(data$ymax)) {
+      y <- resolve_rect(
+        data[["ymin"]], data[["ymax"]],
+        data[["y"]], data[["height"]] %||% params$height
+      )
+      i <- lengths(y) > 1
+      data[c("ymin", "ymax")[i]] <- y[i]
+    }
+    check_required_aesthetics(
+      self$non_missing_aes,
+      names(data),
+      snake_class(self)
+    )
+    data
+  },
 
   draw_panel = function(self, data, panel_params, coord, lineend = "butt", linejoin = "mitre") {
     data <- check_linewidth(data, snake_class(self))
@@ -73,3 +103,26 @@ GeomRect <- ggproto("GeomRect", Geom,
 
   rename_size = TRUE
 )
+
+resolve_rect <- function(min = NULL, max = NULL, center = NULL, length = NULL) {
+  if (is.null(min) && is.null(max)) {
+    min <- center - 0.5 * length
+    max <- center + 0.5 * length
+    return(list(min = min, max = max))
+  }
+  if (is.null(min)) {
+    if (is.null(center)) {
+      min <- max - length
+    } else {
+      min <- max - 2 * (max - center)
+    }
+  }
+  if (is.null(max)) {
+    if (is.null(center)) {
+      max <- min + length
+    } else {
+      max <- min + 2 * (center - min)
+    }
+  }
+  list(min = min, max = max)
+}

R/geom-tile.R

@@ -1,12 +1,11 @@
 #' Rectangles
 #'
 #' `geom_rect()` and `geom_tile()` do the same thing, but are
-#' parameterised differently: `geom_rect()` uses the locations of the four
-#' corners (`xmin`, `xmax`, `ymin` and `ymax`), while
-#' `geom_tile()` uses the center of the tile and its size (`x`,
-#' `y`, `width`, `height`). `geom_raster()` is a high
-#' performance special case for when all the tiles are the same size, and no
-#' pattern fills are applied.
+#' parameterised differently: `geom_tile()` uses the center of the tile and its
+#' size (`x`, `y`, `width`, `height`), while `geom_rect()` can use those or the
+#' locations of the corners (`xmin`, `xmax`, `ymin` and `ymax`).
+#' `geom_raster()` is a high performance special case for when all the tiles
+#' are the same size, and no pattern fills are applied.
 #'
 #' @eval rd_aesthetics("geom", "tile", "Note that `geom_raster()` ignores `colour`.")
 #' @inheritParams layer
@@ -15,11 +14,9 @@
 #' @export
 #'
 #' @details
-#' `geom_rect()` and `geom_tile()`'s respond differently to scale
-#' transformations due to their parameterisation. In `geom_rect()`, the scale
-#' transformation is applied to the corners of the rectangles. In `geom_tile()`,
-#' the transformation is applied only to the centres and its size is determined
-#' after transformation.
+#' Please note that the `width` and `height` aesthetics are not true position
+#' aesthetics and therefore are not subject to scale transformation. It is
+#' only after transformation that these aesthetics are applied.
 #'
 #' @examples
 #' # The most common use for rectangles is to draw a surface. You always want

tests/testthat/test-geom-rect.R

@@ -0,0 +1,36 @@
+test_that("geom_rect can derive corners", {
+
+  corners <- c("xmin", "xmax", "ymin", "ymax")
+  full <- data.frame(
+    xmin = c(1, 2), xmax = c(3, 6),
+    ymin = c(1, 2), ymax = c(3, 6),
+    width = c(2, 4), height = c(2, 4),
+    x = c(2, 4), y = c(2, 4)
+  )
+
+  test <- full[, c("xmin", "ymin", "width", "height")]
+  test <- GeomRect$setup_data(test, NULL)
+  expect_equal(full[, corners], test[, corners])
+
+  test <- full[, c("xmin", "ymin", "x", "y")]
+  test <- GeomRect$setup_data(test, NULL)
+  expect_equal(full[, corners], test[, corners])
+
+  test <- full[, c("x", "y", "width", "height")]
+  test <- GeomRect$setup_data(test, NULL)
+  expect_equal(full[, corners], test[, corners])
+
+  test <- full[, c("xmax", "ymax", "width", "height")]
+  test <- GeomRect$setup_data(test, NULL)
+  expect_equal(full[, corners], test[, corners])
+
+  test <- full[, c("xmax", "ymax", "x", "y")]
+  test <- GeomRect$setup_data(test, NULL)
+  expect_equal(full[, corners], test[, corners])
+
+  test <- full[, c("x", "y")]
+  expect_error(
+    GeomRect$setup_data(test, NULL),
+    "requires the following missing aesthetics"
+  )
+})