add plot.title.position theme element

Author: clauswilke

R/plot-build.r

@@ -261,20 +261,36 @@ ggplot_gtable.ggplot_built <- function(data) {
   caption <- element_render(theme, "plot.caption", plot$labels$caption, margin_y = TRUE)
   caption_height <- grobHeight(caption)
 
-  pans <- plot_table$layout[grepl("^panel", plot_table$layout$name), ,
-    drop = FALSE]
+  # positioning of title, subtitle, and caption is governed by plot.title.position
+  #   "panel" means align to the panel(s)
+  #   "plot" means align to the entire plot (except margins and tag)
+  title_pos <- theme$plot.title.position %||% "panel"
+
+  if (!(title_pos %in% c("panel", "plot"))) {
+    stop('plot.title.position should be either "panel" or "plot".', call. = FALSE)
+  }
+
+  if (title_pos == "panel") {
+    pans <- plot_table$layout[grepl("^panel", plot_table$layout$name), ,
+      drop = FALSE]
+    title_l = min(pans$l)
+    title_r = max(pans$r)
+  } else {
+    title_l = 1
+    title_r = ncol(plot_table)
+  }
 
   plot_table <- gtable_add_rows(plot_table, subtitle_height, pos = 0)
   plot_table <- gtable_add_grob(plot_table, subtitle, name = "subtitle",
-    t = 1, b = 1, l = min(pans$l), r = max(pans$r), clip = "off")
+    t = 1, b = 1, l = title_l, r = title_r, clip = "off")
 
   plot_table <- gtable_add_rows(plot_table, title_height, pos = 0)
   plot_table <- gtable_add_grob(plot_table, title, name = "title",
-    t = 1, b = 1, l = min(pans$l), r = max(pans$r), clip = "off")
+    t = 1, b = 1, l = title_l, r = title_r, clip = "off")
 
   plot_table <- gtable_add_rows(plot_table, caption_height, pos = -1)
   plot_table <- gtable_add_grob(plot_table, caption, name = "caption",
-    t = -1, b = -1, l = min(pans$l), r = max(pans$r), clip = "off")
+    t = -1, b = -1, l = title_l, r = title_r, clip = "off")
 
   plot_table <- gtable_add_rows(plot_table, unit(0, 'pt'), pos = 0)
   plot_table <- gtable_add_cols(plot_table, unit(0, 'pt'), pos = 0)

R/theme-defaults.r

@@ -214,6 +214,7 @@ theme_grey <- function(base_size = 11, base_family = "",
                            hjust = 0, vjust = 1,
                            margin = margin(b = half_line)
                          ),
+    plot.title.position = "panel",
     plot.subtitle =      element_text( # font size "regular"
                            hjust = 0, vjust = 1,
                            margin = margin(b = half_line)

R/theme-elements.r

@@ -370,6 +370,7 @@ el_def <- function(class = NULL, inherit = NULL, description = NULL) {
 
   plot.background     = el_def("element_rect", "rect"),
   plot.title          = el_def("element_text", "title"),
+  plot.title.position = el_def("character"),
   plot.subtitle       = el_def("element_text", "title"),
   plot.caption        = el_def("element_text", "title"),
   plot.tag            = el_def("element_text", "title"),