Re: `window-hscroll' does not report correct value when `text-scale-mode' is on

[路客]

>I don't think I understand what needs fixing.  Is this question
>different from the second one, i.e. if you can compute a suitable
>value requested in your second question, is there something else that
>needs fixing in ruler-mode?  If so, what else needs fixing?

There are three problems result from the same reason:

First, when you use text-scale-mode (S-leftmouse) to decrease font
size, you will first see the ruler becomes smaller than the
`window-width'.

Second, when you move the cursor rightwards, you will see the
"indicator" of the cursor not at the correct x-coordinate as our cursor.

Third, when you edit a long line with line-wrap mode off, the
`window-hscroll' value it used is not scaled so the ruler will start
showing incorrect positions. It get more worse as the line grows longer.


>  (* (/ (window-hscroll) (frame-char-width)) (default-font-width))

Cool! After some experiment I think it should be

(/ (* (window-hscroll) (frame-char-width)) (default-font-width))

This can give the the *exact* value of scaled window-hscroll. I
tried to round it up to the closest integer but it seems not
required (I am not 100% sure).

Here is my patch to ruler-mode, please review my changes. I don't
think my function names are good. Thanks!
--------------

diff --git a/lisp/ruler-mode.el b/lisp/ruler-mode.el
index 4f09a1887f5..36d399c7c91 100644
--- a/lisp/ruler-mode.el
+++ b/lisp/ruler-mode.el
@@ -360,6 +360,21 @@ ruler-mode-dragged-symbol
 That is `fill-column', `comment-column', `goal-column', or nil when
 nothing is dragged.")

+(defun ruler-mode-text-scaled-width (width)
+  "Compute scaled text width according to current font scaling.
+Convert a width of char units into a text-scaled char width units,
+Ex. `window-hscroll'. The return value is rounded up to the closest
+integer."
+  (/ (* width (frame-char-width)) (default-font-width)))
+
+(defun ruler-mode-window-hscroll ()
+  "Text scaled `window-hscroll'."
+  (ruler-mode-text-scaled-width (window-hscroll)))
+
+(defun ruler-mode-window-width ()
+  "Text scaled `window-width'."
+  (ruler-mode-text-scaled-width (window-width)))
+
 (defun ruler-mode-mouse-grab-any-column (start-event)
   "Drag a column symbol on the ruler.
 Start dragging on mouse down event START-EVENT, and update the column
@@ -372,9 +387,9 @@ ruler-mode-mouse-grab-any-column
     (save-selected-window
       (select-window (posn-window start))
       (setq col  (ruler-mode-window-col (car (posn-col-row start)))
-            newc (+ col (window-hscroll)))
+            newc (+ col (ruler-mode-window-hscroll)))
       (and
-       (>= col 0) (< col (window-width))
+       (>= col 0) (< col (ruler-mode-window-width))
        (cond

         ;; Handle the fill column.
@@ -457,8 +472,8 @@ ruler-mode-mouse-drag-any-column
     (save-selected-window
       (select-window (posn-window start))
       (setq col  (ruler-mode-window-col (car (posn-col-row end)))
-            newc (+ col (window-hscroll)))
-      (when (and (>= col 0) (< col (window-width)))
+            newc (+ col (ruler-mode-window-hscroll)))
+      (when (and (>= col 0) (< col (ruler-mode-window-width)))
         (set ruler-mode-dragged-symbol newc)))))

 (defun ruler-mode-mouse-add-tab-stop (start-event)
@@ -473,8 +488,8 @@ ruler-mode-mouse-add-tab-stop
         (save-selected-window
           (select-window (posn-window start))
           (setq col (ruler-mode-window-col (car (posn-col-row start)))
-                ts  (+ col (window-hscroll)))
-          (and (>= col 0) (< col (window-width))
+                ts  (+ col (ruler-mode-window-hscroll)))
+          (and (>= col 0) (< col (ruler-mode-window-width))
                (not (member ts tab-stop-list))
                (progn
                  (message "Tab stop set to %d" ts)
@@ -494,8 +509,8 @@ ruler-mode-mouse-del-tab-stop
         (save-selected-window
           (select-window (posn-window start))
           (setq col (ruler-mode-window-col (car (posn-col-row start)))
-                ts  (+ col (window-hscroll)))
-          (and (>= col 0) (< col (window-width))
+                ts  (+ col (ruler-mode-window-hscroll)))
+          (and (>= col 0) (< col (ruler-mode-window-width))
                (member ts tab-stop-list)
                (progn
                  (message "Tab stop at %d deleted" ts)
@@ -648,11 +663,11 @@ ruler-mode-space

 (defun ruler-mode-ruler ()
   "Compute and return a header line ruler."
-  (let* ((w (window-width))
+  (let* ((w (ruler-mode-window-width))
          (m (window-margins))
          (f (window-fringes))
          (i 0)
-         (j (window-hscroll))
+         (j (ruler-mode-window-hscroll))
          ;; Setup the scrollbar, fringes, and margins areas.
          (lf (ruler-mode-space
               'left-fringe


Best regards,
Luke Lee