Allow putting alternating colors on vtable rows

* doc/misc/vtable.texi (Making A Table): Document it.
* lisp/emacs-lisp/vtable.el (vtable): Add :row-colors.
(make-vtable): Ditto.
(vtable--compute-colors, vtable--color-blend): New functions.
(vtable--insert-line): Take a line number argument and adjust
callers.

1 files changed, 11 insertions, 1 deletions

diff --git a/doc/misc/vtable.texi b/doc/misc/vtable.texi
index 4f7b722a289..77cb8663af4 100644
--- a/doc/misc/vtable.texi
+++ b/doc/misc/vtable.texi
@@ -387,11 +387,21 @@ The face to be used.  This defaults to @code{vtable}.  This face
 doesn't override the faces in the data, or the faces supplied by the
 getter and formatter functions.
 
+@item :row-colors
+If present, this should be a list of color names to be used as the
+background color on the rows.  If there are fewer colors here than
+there are rows, the rows will be repeated.  The most common use
+case here is to have alternating background colors on the rows, so
+this would usually be a list of two colors.
+
 @item :column-colors
 If present, this should be a list of color names to be used as the
 background color on the columns.  If there are fewer colors here than
 there are columns, the colors will be repeated.  The most common use
-case here is to have alternating background colors on the columns.
+case here is to have alternating background colors on the columns, so
+this would usually be a list of two colors.  If both
+@code{:row-colors} and @code{:column-colors} is present, the colors
+will be ``blended'' to produce the final colors in the table.
 
 @item :actions
 This uses the same syntax as @code{define-keymap}, but doesn't refer