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.

2 files changed, 61 insertions, 12 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
diff --git a/lisp/emacs-lisp/vtable.el b/lisp/emacs-lisp/vtable.el
index 3e521c94a5c..e0010434447 100644
--- a/lisp/emacs-lisp/vtable.el
+++ b/lisp/emacs-lisp/vtable.el
@@ -64,6 +64,8 @@
    (sort-by :initarg :sort-by :accessor vtable-sort-by)
    (ellipsis :initarg :ellipsis :accessor vtable-ellipsis)
    (column-colors :initarg :column-colors :accessor vtable-column-colors)
+   (row-colors :initarg :row-colors :accessor vtable-row-colors)
+   (-cached-colors :initform nil :accessor vtable--cached-colors)
    (-cache :initform (make-hash-table :test #'equal)))
   "A object to hold the data for a table.")
 
@@ -91,6 +93,7 @@
                             sort-by
                             (ellipsis t)
                             (insert t)
+                            row-colors
                             column-colors)
   "Create and insert a vtable at point.
 The vtable object is returned.  If INSERT is nil, the table won't
@@ -130,10 +133,15 @@ be inserted."
                         :keymap keymap
                         :separator-width separator-width
                         :sort-by sort-by
+                        :row-colors row-colors
                         :column-colors column-colors
                         :ellipsis ellipsis)))
     ;; Compute missing column data.
     (setf (vtable-columns table) (vtable--compute-columns table))
+    ;; Compute colors if we have to mix them.
+    (when (and row-colors column-colors)
+      (setf (vtable--cached-colors table)
+            (vtable--compute-colors row-colors column-colors)))
     (unless sort-by
       (seq-do-indexed (lambda (column index)
                         (when (vtable-column-primary column)
@@ -144,6 +152,20 @@ be inserted."
       (vtable-insert table))
     table))
 
+(defun vtable--compute-colors (row-colors column-colors)
+  (cl-loop for row in row-colors
+           collect (cl-loop for column in column-colors
+                            collect (vtable--color-blend row column))))
+
+;;; FIXME: This is probably not the right way to blend two colors, is
+;;; it?
+(defun vtable--color-blend (color1 color2)
+  (cl-destructuring-bind (r g b)
+      (mapcar (lambda (n) (* (/ n 2) 255.0))
+              (cl-mapcar #'+ (color-name-to-rgb color1)
+                         (color-name-to-rgb color2)))
+    (format "#%02X%02X%02X" r g b)))
+
 ;;; Interface utility functions.
 
 (defun vtable-current-table ()
@@ -219,7 +241,8 @@ If it can't be found, return nil and don't move point."
         (error "Can't find the old object"))
       (setcar (cdr objects) object))
     ;; Then update the cache...
-    (let ((line (assq old-object (car (vtable--cache table)))))
+    (let* ((line-number (seq-position old-object (car (vtable--cache table))))
+           (line (elt (car (vtable--cache table)) line-number)))
       (unless line
         (error "Can't find cached object"))
       (setcar line object)
@@ -230,7 +253,8 @@ If it can't be found, return nil and don't move point."
         (let ((keymap (get-text-property (point) 'keymap))
               (start (point)))
           (delete-line)
-          (vtable--insert-line table line (nth 1 (vtable--cache table))
+          (vtable--insert-line table line line-number
+                               (nth 1 (vtable--cache table))
                                (vtable--spacer table))
           (add-text-properties start (point) (list 'keymap keymap
                                                    'vtable table))))
@@ -285,7 +309,10 @@ This also updates the displayed table."
           (unless (vtable-goto-object after-object)
             (vtable-end-of-table))))
       (let ((start (point)))
-        (vtable--insert-line table line (nth 1 cache) (vtable--spacer table))
+        ;; FIXME: We have to adjust colors in lines below this if we
+        ;; have :row-colors.
+        (vtable--insert-line table line 0
+                             (nth 1 cache) (vtable--spacer table))
         (add-text-properties start (point) (list 'keymap keymap
                                                  'vtable table)))
       ;; We may have inserted a non-numerical value into a previously
@@ -374,20 +401,26 @@ This also updates the displayed table."
       (setq start (point)))
     (vtable--sort table)
     ;; Insert the data.
-    (dolist (line (car (vtable--cache table)))
-      (vtable--insert-line table line widths spacer
-                           ellipsis ellipsis-width))
+    (let ((line-number 0))
+      (dolist (line (car (vtable--cache table)))
+        (vtable--insert-line table line line-number widths spacer
+                             ellipsis ellipsis-width)
+        (setq line-number (1+ line-number))))
     (add-text-properties start (point)
                          (list 'keymap (vtable--make-keymap table)
                                'rear-nonsticky t
                                'vtable table))
     (goto-char start)))
 
-(defun vtable--insert-line (table line widths spacer
+(defun vtable--insert-line (table line line-number widths spacer
                                   &optional ellipsis ellipsis-width)
   (let ((start (point))
         (columns (vtable-columns table))
-        (colors (vtable-column-colors table)))
+        (column-colors
+         (if (vtable-row-colors table)
+             (elt (vtable--cached-colors table)
+                  (mod line-number (length (vtable-row-colors table))))
+           (vtable-column-colors table))))
     (seq-do-indexed
      (lambda (elem index)
        (let ((value (nth 0 elem))
@@ -449,14 +482,20 @@ This also updates the displayed table."
                                  (list 'space
                                        :width (list spacer)))))
            (put-text-property start (point) 'vtable-column index)
-           (when colors
+           (when column-colors
              (add-face-text-property
               start (point)
               (list :background
-                    (elt colors (mod index (length colors)))))))))
+                    (elt column-colors (mod index (length column-colors)))))))))
      (cdr line))
     (insert "\n")
-    (put-text-property start (point) 'vtable-object (car line))))
+    (put-text-property start (point) 'vtable-object (car line))
+    (unless column-colors
+      (when-let ((row-colors (vtable-row-colors table)))
+        (add-face-text-property
+         start (point)
+         (list :background
+               (elt row-colors (mod line-number (length row-colors)))))))))
 
 (defun vtable--cache-key ()
   (cons (frame-terminal) (window-width)))