\path markup command computes incorrect extents when using rmoveto after closepath

[Aaron Hill]

The logic within the \path markup command ignores the effect of 
closepath when converting relative coordinates to absolute ones.  
closepath moves the pen back to the starting point of the path.  
Relative coordinates are based on the current pen position, not the most 
recently specified point.  When rmoveto is used after closepath, the 
value of current-point will be incorrect.

Here is an example showing the problem:

%%%%
\version "2.19.83"

% Here is the expected result (using moveto):
\markup \box \path #0.1 #'(
  (moveto 2 3) (rlineto 1 1) (rlineto 0 -1) (closepath)
  (moveto 3.5 3) (rlineto 1 1) (rlineto -1 0) (closepath))

% Here is the actual result (using rmoveto):
\markup \box \path #0.1 #'(
  (moveto 2 3) (rlineto 1 1) (rlineto 0 -1) (closepath)
  (rmoveto 1.5 0) (rlineto 1 1) (rlineto -1 0) (closepath))

% Here is a picture of what \path *thinks* is going on:
\markup \box \overlay {
  \path #0.1 #'(
    (moveto 2 3) (rlineto 1 1) (rlineto 0 -1) (closepath)
    (rmoveto 1.5 0) (rlineto 1 1) (rlineto -1 0) (closepath))
  \with-color #red \path #0.1 #'(
    (moveto 4.5 3) (rlineto 1 1) (rlineto -1 0) (closepath))
}
%%%%

The following patch seems to address the issue:

====
--- define-markup-commands.scm.bak      2020-01-19 22:09:02.904948800 
-0800
+++ define-markup-commands.scm  2020-01-19 22:13:20.858573300 -0800
@@ -1179,8 +1179,15 @@
 }
 @end lilypond"
   (let* ((half-thickness (/ thickness 2))
+         (start-point '())
          (current-point '(0 . 0))
-         (set-point (lambda (lst) (set! current-point lst)))
+         (set-point (lambda (lst)
+                       (if (null? start-point)
+                         (set! start-point lst))
+                       (set! current-point lst)))
+         (reset-point (lambda ()
+                        (set! current-point start-point)
+                        (set! start-point '())))
          (relative? (lambda (x)
                       (string-prefix? "r" (symbol->string (car x)))))
          ;; For calculating extents, we want to modify the command
@@ -1224,7 +1231,7 @@
                                 (drop x 1))
                                ;; keep closepath for filtering;
                                ;; see `without-closepath'.
-                               (else x)))
+                               (else (reset-point) x)))
                             commands))
          ;; path-min-max does not accept 0-arg lists,
          ;; and since closepath does not affect extents, filter
====


-- Aaron Hill

path-bounding-bug.cropped.png
Description: PNG image