Calculate constant descender heights, regardless of label content. (#2471)

* Calculate constant descender heights, regardless of label content. Fixes #2288

* Make themes more visually consistent. Also fix spacing bug for multi-line legend titles.

* gracefully handle missing fontsize in theme (e.g., if legend.title has been set to element_blank())

* update vdiffr templates

Author: clauswilke

NEWS.md

@@ -308,6 +308,11 @@ up correct aspect ratio, and draws a graticule.
 
 * Default themes use `rel()` to set line widths (@baptiste).
 
+* Themes were tweaked for visual consistency and more graceful behavior when changing
+  the base font size. All absolute heights or widths were replaced with heights or 
+  widths that are proportional to the base font size. One relative font size
+  was eliminated. (@clauswilke)
+
 ### Other
 
 * `fortify()` gains a method for tbls (@karawoo, #2218)
@@ -338,6 +343,8 @@ up correct aspect ratio, and draws a graticule.
   summarise the layout, coordinate systems, and layers, of a built ggplot object
   (#2034, @wch). This provides a tested API that (e.g.) shiny can depend on.
 
+* The height of descenders is now calculated solely on font metrics and doesn't change with the specific letters in the string. This fixes minor alignment issues with plot titles, subtitles, and legend titles. (#2288, @clauswilke)
+
 * Update startup messages to reflect new resources. (#2410, @mine-cetinkaya-rundel)
 
 # ggplot2 2.2.1

R/guide-colorbar.r

@@ -282,9 +282,14 @@ guide_gengrob.colorbar <- function(guide, theme) {
   if (!guide$draw.llim) tic_pos.c <- tic_pos.c[-length(tic_pos.c)]
 
   # title
+
+  # obtain the theme for the legend title. We need this both for the title grob
+  # and to obtain the title fontsize.
+  title.theme <- guide$title.theme %||% calc_element("legend.title", theme)
+
   grob.title <- ggname("guide.title",
     element_grob(
-      guide$title.theme %||% calc_element("legend.title", theme),
+      title.theme,
       label = guide$title,
       hjust = guide$title.hjust %||% theme$legend.title.align %||% 0,
       vjust = guide$title.vjust %||% 0.5
@@ -296,10 +301,14 @@ guide_gengrob.colorbar <- function(guide, theme) {
   title_width.c <- c(title_width)
   title_height <- convertHeight(grobHeight(grob.title), "mm")
   title_height.c <- c(title_height)
+  title_fontsize <- title.theme$size
+  if (is.null(title_fontsize)) title_fontsize <- 0
 
   # gap between keys etc
   hgap <- width_cm(theme$legend.spacing.x  %||% unit(0.3, "line"))
-  vgap <- height_cm(theme$legend.spacing.y %||% (0.5 * unit(title_height, "cm")))
+  # multiply by 5 instead of 0.5 due to unit error below. this needs to be fixed
+  # separately (pull request pending).
+  vgap <- height_cm(theme$legend.spacing.y %||% (5 * unit(title_fontsize, "pt")))
 
   # label
   label.theme <- guide$label.theme %||% calc_element("legend.text", theme)

R/guide-legend.r

@@ -325,9 +325,13 @@ guide_gengrob.legend <- function(guide, theme) {
 
   nbreak <- nrow(guide$key)
 
+  # obtain the theme for the legend title. We need this both for the title grob
+  # and to obtain the title fontsize.
+  title.theme <- guide$title.theme %||% calc_element("legend.title", theme)
+
   grob.title <- ggname("guide.title",
     element_grob(
-      guide$title.theme %||% calc_element("legend.title", theme),
+      title.theme,
       label = guide$title,
       hjust = guide$title.hjust %||% theme$legend.title.align %||% 0,
       vjust = guide$title.vjust %||% 0.5,
@@ -338,10 +342,12 @@ guide_gengrob.legend <- function(guide, theme) {
 
   title_width <- width_cm(grob.title)
   title_height <- height_cm(grob.title)
+  title_fontsize <- title.theme$size
+  if (is.null(title_fontsize)) title_fontsize <- 0
 
   # gap between keys etc
   hgap <- width_cm(theme$legend.spacing.x  %||% unit(0.3, "line"))
-  vgap <- height_cm(theme$legend.spacing.y %||% (0.5 * unit(title_height, "cm")))
+  vgap <- height_cm(theme$legend.spacing.y %||% (0.5 * unit(title_fontsize, "pt")))
 
   # Labels
   if (!guide$label || is.null(guide$key$.label)) {

R/margins.R

@@ -68,11 +68,20 @@ title_spec <- function(label, x, y, hjust, vjust, angle, gp = gpar(),
     gp = gp
   )
 
-  # The grob dimensions don't include the text descenders, so add on using
-  # a little trigonometry. This is only exactly correct when vjust = 1.
-  descent <- descentDetails(text_grob)
-  text_height <- unit(1, "grobheight", text_grob) + cos(angle / 180 * pi) * descent
-  text_width <- unit(1, "grobwidth", text_grob) + sin(angle / 180 * pi) * descent
+  # The grob dimensions don't include the text descenders, so these need to be added
+  # manually. Because descentDetails calculates the actual descenders of the specific
+  # text label, which depends on the label content, we replace the label with one that
+  # has the common letters with descenders. This guarantees that the grob always has
+  # the same height regardless of whether the text actually contains letters with
+  # descenders or not. The same happens automatically with ascenders already.
+  temp <- editGrob(text_grob, label = "gjpqyQ")
+  descent <- descentDetails(temp)
+
+  # Use trigonometry to calculate grobheight and width for rotated grobs. This is only
+  # exactly correct when vjust = 1. We need to take the absolute value so we don't make
+  # the grob smaller when it's flipped over.
+  text_height <- unit(1, "grobheight", text_grob) + abs(cos(angle / 180 * pi)) * descent
+  text_width <- unit(1, "grobwidth", text_grob) + abs(sin(angle / 180 * pi)) * descent
 
   if (isTRUE(debug)) {
     children <- gList(

R/theme-defaults.r

@@ -69,8 +69,19 @@ NULL
 theme_grey <- function(base_size = 11, base_family = "",
                        base_line_size = base_size / 22,
                        base_rect_size = base_size / 22) {
+
+  # The half-line (base-fontsize / 2) sets up the basic vertical
+  # rhythm of the theme. Most margins will be set to this value.
+  # However, when we work with relative sizes, we may want to multiply
+  # `half_line` with the appropriate relative size. This applies in
+  # particular for axis tick sizes. And also, for axis ticks and
+  # axis titles, `half_size` is too large a distance, and we use `half_size/2`
+  # instead.
   half_line <- base_size / 2
 
+  # Throughout the theme, we use three font sizes, `base_size` (`rel(1)`)
+  # for normal, `rel(0.8)` for small, and `rel(1.2)` for large.
+
   theme(
     # Elements in this first block aren't used directly, but are inherited
     # by others
@@ -100,29 +111,29 @@ theme_grey <- function(base_size = 11, base_family = "",
     axis.ticks =         element_line(colour = "grey20"),
     axis.ticks.length =  unit(half_line / 2, "pt"),
     axis.title.x =       element_text(
-                           margin = margin(t = half_line),
+                           margin = margin(t = half_line / 2),
                            vjust = 1
                          ),
     axis.title.x.top =   element_text(
-                           margin = margin(b = half_line),
+                           margin = margin(b = half_line / 2),
                            vjust = 0
                          ),
     axis.title.y =       element_text(
                            angle = 90,
-                           margin = margin(r = half_line),
+                           margin = margin(r = half_line / 2),
                            vjust = 1
                          ),
     axis.title.y.right = element_text(
                            angle = -90,
-                           margin = margin(l = half_line),
+                           margin = margin(l = half_line / 2),
                            vjust = 0
                          ),
 
     legend.background =  element_rect(colour = NA),
-    legend.spacing =     unit(0.4, "cm"),
+    legend.spacing =     unit(2 * half_line, "pt"),
     legend.spacing.x =    NULL,
     legend.spacing.y =    NULL,
-    legend.margin =      margin(0.2, 0.2, 0.2, 0.2, "cm"),
+    legend.margin =      margin(half_line, half_line, half_line, half_line),
     legend.key =         element_rect(fill = "grey95", colour = "white"),
     legend.key.size =    unit(1.2, "lines"),
     legend.key.height =  NULL,
@@ -137,7 +148,7 @@ theme_grey <- function(base_size = 11, base_family = "",
     legend.box =         NULL,
     legend.box.margin =  margin(0, 0, 0, 0, "cm"),
     legend.box.background = element_blank(),
-    legend.box.spacing = unit(0.4, "cm"),
+    legend.box.spacing = unit(2 * half_line, "pt"),
 
     panel.background =   element_rect(fill = "grey92", colour = NA),
     panel.border =       element_blank(),
@@ -152,31 +163,30 @@ theme_grey <- function(base_size = 11, base_family = "",
     strip.text =         element_text(
                            colour = "grey10",
                            size = rel(0.8),
-                           margin = margin(half_line, half_line, half_line, half_line)
+                           margin = margin(0.8 * half_line, 0.8 * half_line, 0.8 * half_line, 0.8 * half_line)
                          ),
     strip.text.x =       NULL,
     strip.text.y =       element_text(angle = -90),
     strip.placement =    "inside",
     strip.placement.x =  NULL,
     strip.placement.y =  NULL,
-    strip.switch.pad.grid = unit(0.1, "cm"),
-    strip.switch.pad.wrap = unit(0.1, "cm"),
+    strip.switch.pad.grid = unit(half_line / 2, "pt"),
+    strip.switch.pad.wrap = unit(half_line / 2, "pt"),
 
     plot.background =    element_rect(colour = "white"),
-    plot.title =         element_text(
+    plot.title =         element_text( # font size "large"
                            size = rel(1.2),
                            hjust = 0, vjust = 1,
-                           margin = margin(b = half_line * 1.2)
+                           margin = margin(b = half_line)
                          ),
-    plot.subtitle =      element_text(
-                           size = rel(0.9),
+    plot.subtitle =      element_text( # font size "regular"
                            hjust = 0, vjust = 1,
-                           margin = margin(b = half_line * 0.9)
+                           margin = margin(b = half_line)
                          ),
-    plot.caption =       element_text(
-                           size = rel(0.9),
+    plot.caption =       element_text( # font size "small"
+                           size = rel(0.8),
                            hjust = 1, vjust = 1,
-                           margin = margin(t = half_line * 0.9)
+                           margin = margin(t = half_line)
                          ),
     plot.margin =        margin(half_line, half_line, half_line, half_line),
 
@@ -248,7 +258,7 @@ theme_linedraw <- function(base_size = 11, base_family = "",
       strip.text       = element_text(
                            colour = "white",
                            size = rel(0.8),
-                           margin = margin(half_line, half_line, half_line, half_line)
+                           margin = margin(0.8 * half_line, 0.8 * half_line, 0.8 * half_line, 0.8 * half_line)
                          ),
 
       complete = TRUE
@@ -290,7 +300,7 @@ theme_light <- function(base_size = 11, base_family = "",
       strip.text       = element_text(
                            colour = "white",
                            size = rel(0.8),
-                           margin = margin(half_line, half_line, half_line, half_line)
+                           margin = margin(0.8 * half_line, 0.8 * half_line, 0.8 * half_line, 0.8 * half_line)
                          ),
 
       complete = TRUE
@@ -332,7 +342,7 @@ theme_dark <- function(base_size = 11, base_family = "",
       strip.text       = element_text(
                            colour = "grey90",
                            size = rel(0.8),
-                           margin = margin(half_line, half_line, half_line, half_line)
+                           margin = margin(0.8 * half_line, 0.8 * half_line, 0.8 * half_line, 0.8 * half_line)
                          ),
 
       complete = TRUE
@@ -420,25 +430,24 @@ theme_void <- function(base_size = 11, base_family = "",
     legend.text =        element_text(size = rel(0.8)),
     legend.title =       element_text(hjust = 0),
     strip.text =         element_text(size = rel(0.8)),
-    strip.switch.pad.grid = unit(0.1, "cm"),
-    strip.switch.pad.wrap = unit(0.1, "cm"),
+    strip.switch.pad.grid = unit(half_line / 2, "pt"),
+    strip.switch.pad.wrap = unit(half_line / 2, "pt"),
     panel.ontop =        FALSE,
     panel.spacing =      unit(half_line, "pt"),
     plot.margin =        unit(c(0, 0, 0, 0), "lines"),
     plot.title =         element_text(
                            size = rel(1.2),
                            hjust = 0, vjust = 1,
-                           margin = margin(t = half_line * 1.2)
+                           margin = margin(t = half_line)
                          ),
     plot.subtitle =      element_text(
-                           size = rel(0.9),
                            hjust = 0, vjust = 1,
-                           margin = margin(t = half_line * 0.9)
+                           margin = margin(t = half_line)
                          ),
     plot.caption =       element_text(
-                           size = rel(0.9),
+                           size = rel(0.8),
                            hjust = 1, vjust = 1,
-                           margin = margin(t = half_line * 0.9)
+                           margin = margin(t = half_line)
                          ),
 
     complete = TRUE
@@ -480,26 +489,26 @@ theme_test <- function(base_size = 11, base_family = "",
     axis.ticks =         element_line(colour = "grey20"),
     axis.ticks.length =  unit(half_line / 2, "pt"),
     axis.title.x =       element_text(
-                           margin = margin(t = half_line),
+                           margin = margin(t = half_line / 2),
                            vjust = 1
                          ),
     axis.title.x.top =   element_text(
-                           margin = margin(b = half_line),
+                           margin = margin(b = half_line / 2),
                            vjust = 0
                          ),
     axis.title.y =       element_text(
                            angle = 90,
-                           margin = margin(r = half_line),
+                           margin = margin(r = half_line / 2),
                            vjust = 1
                          ),
     axis.title.y.right = element_text(
                            angle = -90,
-                           margin = margin(l = half_line),
+                           margin = margin(l = half_line / 2),
                            vjust = 0
                          ),
 
     legend.background =  element_rect(colour = NA),
-    legend.spacing =     unit(0.4, "cm"),
+    legend.spacing =     unit(2 * half_line, "pt"),
     legend.spacing.x =   NULL,
     legend.spacing.y =   NULL,
     legend.margin =      margin(0, 0, 0, 0, "cm"),
@@ -517,7 +526,7 @@ theme_test <- function(base_size = 11, base_family = "",
     legend.box =         NULL,
     legend.box.margin =  margin(0, 0, 0, 0, "cm"),
     legend.box.background = element_blank(),
-    legend.box.spacing = unit(0.4, "cm"),
+    legend.box.spacing = unit(2 * half_line, "pt"),
 
     panel.background =   element_rect(fill = "white", colour = NA),
     panel.border =       element_rect(fill = NA, colour = "grey20"),
@@ -532,31 +541,30 @@ theme_test <- function(base_size = 11, base_family = "",
     strip.text =         element_text(
                            colour = "grey10",
                            size = rel(0.8),
-                           margin = margin(half_line, half_line, half_line, half_line)
+                           margin = margin(0.8 * half_line, 0.8 * half_line, 0.8 * half_line, 0.8 * half_line)
                          ),
     strip.text.x =       NULL,
     strip.text.y =       element_text(angle = -90),
     strip.placement =    "inside",
     strip.placement.x =  NULL,
     strip.placement.y =  NULL,
-    strip.switch.pad.grid = unit(0.1, "cm"),
-    strip.switch.pad.wrap = unit(0.1, "cm"),
+    strip.switch.pad.grid = unit(half_line / 2, "pt"),
+    strip.switch.pad.wrap = unit(half_line / 2, "pt"),
 
     plot.background =    element_rect(colour = "white"),
     plot.title =         element_text(
                            size = rel(1.2),
                            hjust = 0, vjust = 1,
-                           margin = margin(b = half_line * 1.2)
+                           margin = margin(b = half_line)
                          ),
     plot.subtitle =      element_text(
-                           size = rel(0.9),
                            hjust = 0, vjust = 1,
-                           margin = margin(b = half_line * 0.9)
+                           margin = margin(b = half_line)
                          ),
     plot.caption =       element_text(
-                           size = rel(0.9),
+                           size = rel(0.8),
                            hjust = 1, vjust = 1,
-                           margin = margin(t = half_line * 0.9)
+                           margin = margin(t = half_line)
                          ),
     plot.margin =        margin(half_line, half_line, half_line, half_line),