Add lineend and linejoin params to geom_rect() and geom_tile() (#3050)

NEWS.md

@@ -161,6 +161,10 @@ core developer team.
 * `geom_*()` and `stat_*()` now accepts purrr-style lambda notation
   (@yutannihilation, #3138).
 
+* `geom_tile()` and `geom_rect()` now draw rectangles without notches at the
+  corners. The style of the corner can be controlled by `linejoin` parameters
+  (@yutannihilation, #3050).
+
 # ggplot2 3.1.0
 
 ## Breaking changes

R/geom-rect.r

@@ -3,6 +3,7 @@
 geom_rect <- function(mapping = NULL, data = NULL,
                       stat = "identity", position = "identity",
                       ...,
+                      linejoin = "mitre",
                       na.rm = FALSE,
                       show.legend = NA,
                       inherit.aes = TRUE) {
@@ -15,6 +16,7 @@ geom_rect <- function(mapping = NULL, data = NULL,
     show.legend = show.legend,
     inherit.aes = inherit.aes,
     params = list(
+      linejoin = linejoin,
       na.rm = na.rm,
       ...
     )
@@ -31,7 +33,7 @@ GeomRect <- ggproto("GeomRect", Geom,
 
   required_aes = c("xmin", "xmax", "ymin", "ymax"),
 
-  draw_panel = function(self, data, panel_params, coord) {
+  draw_panel = function(self, data, panel_params, coord, linejoin = "mitre") {
     if (!coord$is_linear()) {
       aesthetics <- setdiff(
         names(data), c("x", "y", "xmin", "xmax", "ymin", "ymax")
@@ -58,7 +60,10 @@ GeomRect <- ggproto("GeomRect", Geom,
           fill = alpha(coords$fill, coords$alpha),
           lwd = coords$size * .pt,
           lty = coords$linetype,
-          lineend = "butt"
+          linejoin = linejoin,
+          # `lineend` is a workaround for Windows and intentionally kept unexposed
+          # as an argument. (c.f. https://github.com/tidyverse/ggplot2/issues/3037#issuecomment-457504667)
+          lineend = if (identical(linejoin, "round")) "round" else "square"
         )
       ))
     }
@@ -69,7 +74,10 @@ GeomRect <- ggproto("GeomRect", Geom,
 
 
 # Convert rectangle to polygon
-# Useful for non-Cartesian coordinate systems where it's easy to work purely in terms of locations, rather than locations and dimensions.
+# Useful for non-Cartesian coordinate systems where it's easy to work purely in
+# terms of locations, rather than locations and dimensions. Note that, though
+# `polygonGrob()` expects an open form, closed form is needed for correct
+# munching (c.f. https://github.com/tidyverse/ggplot2/issues/3037#issuecomment-458406857).
 #
 # @keyword internal
 rect_to_poly <- function(xmin, xmax, ymin, ymax) {

R/geom-tile.r

@@ -10,6 +10,7 @@
 #' @eval rd_aesthetics("geom", "tile")
 #' @inheritParams layer
 #' @inheritParams geom_point
+#' @inheritParams geom_segment
 #' @export
 #' @examples
 #' # The most common use for rectangles is to draw a surface. You always want
@@ -57,6 +58,7 @@
 geom_tile <- function(mapping = NULL, data = NULL,
                       stat = "identity", position = "identity",
                       ...,
+                      linejoin = "mitre",
                       na.rm = FALSE,
                       show.legend = NA,
                       inherit.aes = TRUE) {
@@ -69,6 +71,7 @@ geom_tile <- function(mapping = NULL, data = NULL,
     show.legend = show.legend,
     inherit.aes = inherit.aes,
     params = list(
+      linejoin = linejoin,
       na.rm = na.rm,
       ...
     )

R/legend-draw.r

@@ -80,7 +80,10 @@ draw_key_polygon <- function(data, params, size) {
       fill = alpha(data$fill %||% "grey20", data$alpha),
       lty = data$linetype %||% 1,
       lwd = lwd * .pt,
-      linejoin = "mitre"
+      linejoin = params$linejoin %||% "mitre",
+      # `lineend` is a workaround for Windows and intentionally kept unexposed
+      # as an argument. (c.f. https://github.com/tidyverse/ggplot2/issues/3037#issuecomment-457504667)
+      lineend = if (identical(params$linejoin, "round")) "round" else "square"
   ))
 }