Add draw_key_richtext() function

NAMESPACE

@@ -5,6 +5,7 @@ S3method(element_grob,element_textbox)
 export(GeomRichText)
 export(GeomRichtext)
 export(GeomTextBox)
+export(draw_key_richtext)
 export(element_markdown)
 export(element_textbox)
 export(element_textbox_simple)

R/draw-keys.R

@@ -0,0 +1,89 @@
+#' Key glyph for rich text
+#' 
+#' This is a function for rendering the key in the rich text style when a geom 
+#' needs to be displayed in a legend. It is designed to be provided to a layer's
+#' `key_glyph` argument, either as a function or as `key_glyph = "richtext"`.
+#'
+#' @inheritParams ggplot2::draw_key
+#'
+#' @return A [`richtext_grob`][gridtext::richtext_grob] that represents
+#'   formatted text.
+#' @export
+#'
+#' @examples
+#' ggplot(mtcars, aes(wt, mpg, label = rownames(mtcars))) +
+#'   geom_richtext(aes(colour = factor(cyl)), key_glyph = "richtext")
+draw_key_richtext <- function(data, params, size) {
+
+  # Set text justification
+  data$hjust <- data$hjust %||% 0.5
+  data$vjust <- data$vjust %||% 0.5
+  data$angle <- data$angle %||% 0
+  just <- rotate_just(data$angle, data$hjust, data$vjust)
+
+  # Populate graphical parameters for text
+  text_gp <- gpar(
+    fontsize = (data$size %||% 3.88) * .pt,
+    fontfamily = data$family %||% "",
+    fontface = data$face %||% 1,
+    col = scales::alpha(
+      data$text.colour %||% data$colour %||% "black", 
+      data$alpha %||% NA
+    ),
+    lineheight = data$lineheight %||% 1.2
+  )
+
+  # Populate graphical parameters for text box
+  box_gp <- gpar(
+    col = scales::alpha(
+      data$label.colour %||% data$colour %||% "black",
+      data$alpha %||% NA
+    ),
+    fill = scales::alpha(data$fill %||% "white", data$alpha %||% NA),
+    lwd = (data$label.size %||% 0.25) * .pt
+  )
+
+  grob <- richtext_grob(
+    text = data[["label"]] %||% "a", # prevent partial matching
+    x = unit(just$hjust, "npc"),
+    y = unit(just$vjust, "npc"),
+    rot = data$angle,
+    hjust = just$hjust,
+    vjust = just$vjust,
+    gp = text_gp, 
+    box_gp = box_gp,
+    # Defaults for unit input are the same as `geom_richtext()` formals
+    r = params$label.r %||% unit(0.15, "lines"),
+    padding = params$label.padding %||% 
+      unit(c(0.25, 0.25, 0.25, 0.25), "lines"),
+    margin = params$label.margin %||%
+      unit(c(0, 0, 0, 0), "lines"),
+  )
+
+  # Key drawing functions deal with 1 key at a time, so we can extract the
+  # box's (relative) coordinates from the first child-grob.
+  # The units are given in points
+  x <- range(grob$children[[1]]$xext)
+  y <- range(grob$children[[1]]$yext)
+
+  # Calculate offsets that account for textbox size
+  xoffset <- x[1] * (1 - just$hjust) + x[2] * just$hjust
+  yoffset <- y[1] * (1 - just$vjust) + y[2] * just$vjust
+
+  # We apply offsets to the grob's viewport so that textbox is remains within 
+  # the bounds of the key area
+  grob <- editGrob(
+    grob,
+    vp = viewport(
+      x = unit(0.5, "npc") - unit(xoffset, "pt"),
+      y = unit(0.5, "npc") - unit(yoffset, "pt")
+    )
+  )
+
+  # Calculate size in cm. 
+  # 'x * .pt' converts mm to pt, so 'x / .pt' converts pt to mm
+  # This circumvents `convertWidth(grobWidth(grob), "cm", valueOnly = TRUE)`
+  attr(grob, "width")  <- diff(x) / (10 * .pt)
+  attr(grob, "height") <- diff(y) / (10 * .pt)
+  grob
+}