Memoise descentDetails (#2993)

Author: thomasp85

DESCRIPTION

@@ -20,6 +20,7 @@ Depends:
     R (>= 3.1)
 Imports: 
     digest,
+    grDevices,
     grid,
     gtable (>= 0.1.1),
     lazyeval,
@@ -39,23 +40,23 @@ Suggests:
     ggplot2movies,
     hexbin,
     Hmisc,
+    knitr,
     lattice,
     mapproj,
     maps,
     maptools,
     multcomp,
     munsell,
     nlme,
-    testthat (>= 0.11.0),
-    vdiffr, 
+    profvis,
     quantreg,
-    knitr,
     rgeos,
-    rpart,
     rmarkdown,
+    rpart,
     sf (>= 0.3-4),
     svglite (>= 1.2.0.9001),
-    profvis
+    testthat (>= 0.11.0),
+    vdiffr
 Enhances: sp
 License: GPL-2 | file LICENSE
 URL: http://ggplot2.tidyverse.org, https://github.com/tidyverse/ggplot2

R/margins.R

@@ -63,8 +63,7 @@ title_spec <- function(label, x, y, hjust, vjust, angle, gp = gpar(),
   # 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)
+  descent <- font_descent(gp$fontfamily, gp$fontface, gp$fontsize, gp$cex)
 
   # 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
@@ -329,3 +328,24 @@ rotate_just <- function(angle, hjust, vjust) {
 
   list(hjust = hnew, vjust = vnew)
 }
+descent_cache <- new.env(parent = emptyenv())
+font_descent <- function(family = "", face = "plain", size = 12, cex = 1) {
+  cur_dev <- names(grDevices::dev.cur())
+  key <- paste0(cur_dev, ':', family, ':', face, ":", size, ":", cex)
+
+  descent <- descent_cache[[key]]
+
+  if (is.null(descent)) {
+    descent <- descentDetails(textGrob(
+      label = "gjpqyQ",
+      gp = gpar(
+        fontsize = size,
+        cex = cex,
+        fontfamily = family,
+        fontface = face
+      )
+    ))
+    descent_cache[[key]] <- descent
+  }
+  descent
+}

vignettes/profiling.Rmd

@@ -55,3 +55,9 @@ To keep track of changes focused on improving the performance of gtable they
 are summarised below:
 
 ### v`r packageVersion('ggplot2')`
+
+- **Caching of calls to `grid::descentDetails()`** The absolute biggest offender
+  was the construction of titles. In recent versions this has included calls to
+  `grid::descentDetails()` to ensure that they are aligned across plots, but 
+  this is quite heavy. These calls are now cached so they only have to be 
+  calculated once per font setting.