bootloader: grub: Add gfxmode (resolution) override.

* gnu/bootloader/grub.scm (<grub-theme>): Add `gfxmode' entry.
(eye-candy): Use it.
* doc/guix.texi (Bootloader Configuration): Document it.

1 files changed, 26 insertions, 2 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index df1ba428a5..6e3f175488 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -25923,9 +25923,22 @@ must @emph{not} be an OS device name such as @file{/dev/sda1}.
 @end table
 @end deftp
 
+@cindex HDPI
+@cindex HiDPI
+@cindex resolution
 @c FIXME: Write documentation once it's stable.
-For now only GRUB has theme support. GRUB themes are created using
-the @code{grub-theme} form, which is not documented yet.
+For now only GRUB has theme support.  GRUB themes are created using
+the @code{grub-theme} form, which is not fully documented yet.
+
+@deftp {Data Type} grub-theme
+Data type representing the configuration of the GRUB theme.
+
+@table @asis
+@item @code{gfxmode} (default: @code{'("auto")})
+The GRUB @code{gfxmode} to set (a list of screen resolution strings, see
+@pxref{gfxmode,,, grub, GNU GRUB manual}).
+@end table
+@end deftp
 
 @defvr {Scheme Variable} %default-theme
 This is the default GRUB theme used by the operating system if no
@@ -25936,6 +25949,17 @@ It comes with a fancy background image displaying the GNU and Guix
 logos.
 @end defvr
 
+For example, to override the default resolution, you may use something
+like
+
+@lisp
+(bootloader
+ (grub-configuration
+ ;; @dots{}
+ (theme (grub-theme
+         (inherit %default-theme)
+         (gfxmode '("1024x786x32" "auto"))))))
+@end lisp
 
 @node Invoking guix system
 @section Invoking @code{guix system}