[elpa] externals/valign 81de913 042/198: Property support tabs

[Stefan Monnier]

branch: externals/valign
commit 81de91320e38bb741b62bfe60fb84f891073f06f
Author: Yuan Fu <casouri@gmail.com>
Commit: Yuan Fu <casouri@gmail.com>

    Property support tabs
    
    * valign.el (valign--tab-width): New function.
    (valign--glyph-width-at-point): Treat tabs differently.
---
 valign.el | 37 +++++++++++++++++++++++++++----------
 1 file changed, 27 insertions(+), 10 deletions(-)

diff --git a/valign.el b/valign.el
index bba3140..07dcb77 100644
--- a/valign.el
+++ b/valign.el
@@ -91,6 +91,21 @@ Return nil if not in a cell."
 ;;                      nil
 ;;                      (char-after)))))
 
+(defun valign--tab-width (font)
+  "Return the pixel width of a tab in FONT."
+  ;; FIXME We have to over-estimate the pixel width of a tab.  Since
+  ;; it is very hard to compute the exact width of it (basically Emacs
+  ;; redisplay calculates tab width based one the iterators position
+  ;; on-the-fly, to calculate the exact width of a tab, you need to
+  ;; know it’s _position_, that means calculating from the left edge).
+  (* (or tab-width 8) ;; FIXME For some unknown reason, tab-width is
+                      ;; sometimes nil, someone should investigate.
+     (aref (car (mapcar
+                 #'identity (font-get-glyphs
+                             font
+                             0 1 " ")))
+           4)))
+
 (defun valign--glyph-width-at-point (&optional point)
   "Return the pixel width of the glyph at POINT.
 The buffer has to be visible.  If point is at an image, this
@@ -98,16 +113,18 @@ function doens’t return the image’s width, but the 
underlining
 character’s glyph width."
   (let* ((p (or point (point))))
     ;; car + mapcar to translate the vector to a list.
-    (aref (car (mapcar
-                #'identity (font-get-glyphs
-                            ;; (font-at 0 nil (buffer-substring p (1+
-                            ;; p))) doesn’t work, the font is
-                            ;; sometimes wrong.  (font-at p) doesn’t
-                            ;; work, because it requires the buffer to
-                            ;; be visible.
-                            (font-at p)
-                            p (1+ p))))
-          4)))
+    (if (eq (char-after point) ?\t)
+        (valign--tab-width (font-at p))
+      (aref (car (mapcar
+                  #'identity (font-get-glyphs
+                              ;; (font-at 0 nil (buffer-substring p (1+
+                              ;; p))) doesn’t work, the font is
+                              ;; sometimes wrong.  (font-at p) doesn’t
+                              ;; work, because it requires the buffer to
+                              ;; be visible.
+                              (font-at p)
+                              p (1+ p))))
+            4))))
 
 (defun valign--pixel-width-from-to (from to)
   "Return the width of the glyphs from FROM (inclusive) to TO (exclusive).