fix: use full-bleed background rect instead of opaque logo grob

The previous fix applied the plot's background to the logo grob
directly, which made it opaque and covered caption/axis text that
overlaps into the logo area via negative margins.

Instead, wrap the entire arrangeGrob composition in a grobTree with
a background rectGrob behind it. This fills transparent areas (logo
strip, padding gaps) with the plot's background color while keeping
the logo grob itself transparent so overlapping text remains visible.

R/logo.R

@@ -64,15 +64,10 @@ add_logo <- function(plot, logo, margin_param = NULL, font_scale = 1.1,
   position <- match.arg(position)
   at_top <- grepl("top", position)
 
-  # Inherit the plot's background color so the logo strip matches.
-  # make_logo_grob() uses theme_void() (transparent), so without this the
-  # logo area falls back to the device default (white).
+  # Capture the plot's background color so we can fill the entire composed
+  # grob with it.  The logo grob must stay transparent (theme_void) so that
+  # caption/axis text overlapping via negative margins remains visible.
   bg_fill <- plot$theme$plot.background$fill
-  if (!is.null(bg_fill) && !is.na(bg_fill)) {
-    logo <- logo + ggplot2::theme(
-      plot.background = ggplot2::element_rect(fill = bg_fill, color = NA)
-    )
-  }
 
   # Inflate text sizes to compensate for arrangeGrob viewport shrinkage.
   # All theme text elements use rel() sizing, so scaling the root 'text'
@@ -91,8 +86,8 @@ add_logo <- function(plot, logo, margin_param = NULL, font_scale = 1.1,
     } else {
       plot <- plot + theme(plot.margin = unit(c(-14, 7, 7, 7), "pt"))
     }
-    arrangeGrob(logo, plot, heights = c(0.1, 0.93),
-                padding = unit(0.1, "line"))
+    composed <- arrangeGrob(logo, plot, heights = c(0.1, 0.93),
+                            padding = unit(0.1, "line"))
   } else {
     # Bottom placement (original behaviour)
     if(has_caption(plot)) {
@@ -105,8 +100,18 @@ add_logo <- function(plot, logo, margin_param = NULL, font_scale = 1.1,
     } else {
       plot <- plot + theme(plot.margin = unit(c(7, 7, -14, 7), "pt"))
     }
-    arrangeGrob(plot, logo, heights = c(0.93, 0.1),
-                padding = unit(0.1, "line"))
+    composed <- arrangeGrob(plot, logo, heights = c(0.93, 0.1),
+                            padding = unit(0.1, "line"))
+  }
+
+  # Wrap with a full-bleed background rect so any transparent areas (the
+  # logo strip, padding gaps) pick up the plot's background color instead
+  # of the device default (white).
+  if (!is.null(bg_fill) && !is.na(bg_fill)) {
+    bg_rect <- grid::rectGrob(gp = grid::gpar(fill = bg_fill, col = NA))
+    grid::grobTree(bg_rect, composed)
+  } else {
+    composed
   }
 }
 
@@ -174,13 +179,8 @@ has_caption <- function(gg) {
 #' }
 add_logo_ga <- function(plot_list, logo, nrow = 1, widths = NULL,
                         margin_param = NULL, font_scale = 1.1) {
-  # Inherit the background color from the first plot so the logo strip matches
+  # Capture the background color from the first plot
   bg_fill <- plot_list[[1]]$theme$plot.background$fill
-  if (!is.null(bg_fill) && !is.na(bg_fill)) {
-    logo <- logo + ggplot2::theme(
-      plot.background = ggplot2::element_rect(fill = bg_fill, color = NA)
-    )
-  }
 
   # Inflate text sizes to compensate for viewport shrinkage
   if (!is.null(font_scale) && font_scale != 1) {
@@ -215,7 +215,14 @@ add_logo_ga <- function(plot_list, logo, nrow = 1, widths = NULL,
     hold <- arrangeGrob(grobs = plot_list, nrow = 1, ncol = length(plot_list), widths = widths)
   }
 
-  arrangeGrob(hold, logo, heights = c(0.93, .07))
+  composed <- arrangeGrob(hold, logo, heights = c(0.93, .07))
+
+  if (!is.null(bg_fill) && !is.na(bg_fill)) {
+    bg_rect <- grid::rectGrob(gp = grid::gpar(fill = bg_fill, col = NA))
+    grid::grobTree(bg_rect, composed)
+  } else {
+    composed
+  }
 }