bug#28771: 26.0.60; A couple space display property feature requests

[Alex]

Alex <agrambot@gmail.com> writes:

> 1. Specifying the pixel width to the left/center/right of the text area.
>    This is helpful (I believe it's necessary if I want it to be robust)
>    when one wants to pad either side of a string with the same number of
>    pixels and the left side uses (:align-to 0).
>
>    I could use (:width (+ left-fringe left-margin)) for the right
>    padding, but this doesn't take into account line-number display, as
>    well as the scroll-bar width (if it's on the left).
>
> 2. Specifying the pixel position relative to the left or right edge of
>    the window. The right edge of the window currently may be the right
>    edge of the right fringe or the scroll bar, depending on what side it
>    is on. Also, just in the case that in the future the
>    fringe/scroll-bar may not be the outermost elements, there should be
>    a way to explicitly specify one of the edges.

Here's a diff that implements both #1 and #2:

diff --git a/src/xdisp.c b/src/xdisp.c
index b14b7daf2b..d5fa3a1cfe 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -25210,6 +25210,10 @@ calc_pixel_width_or_height (double *res, struct it 
*it, Lisp_Object prop,
                                   + (WINDOW_HAS_FRINGES_OUTSIDE_MARGINS (it->w)
                                      ? WINDOW_RIGHT_FRINGE_WIDTH (it->w)
                                      : 0)));
+          if (EQ (prop, Qleft_edge))
+            return OK_ALIGN_TO (WINDOW_LEFT_PIXEL_EDGE (it->w));
+          if (EQ (prop, Qright_edge))
+            return OK_ALIGN_TO (WINDOW_RIGHT_PIXEL_EDGE (it->w));
        }
       else
        {
@@ -25223,6 +25227,13 @@ calc_pixel_width_or_height (double *res, struct it 
*it, Lisp_Object prop,
            return OK_PIXELS (WINDOW_RIGHT_MARGIN_WIDTH (it->w));
          if (EQ (prop, Qscroll_bar))
            return OK_PIXELS (WINDOW_SCROLL_BAR_AREA_WIDTH (it->w));
+         if (EQ (prop, Qleft))
+            return OK_PIXELS (window_box_left_offset (it->w, TEXT_AREA));
+          if (EQ (prop, Qright))
+           return OK_PIXELS (window_box_right_offset (it->w, TEXT_AREA));
+         if (EQ (prop, Qcenter))
+           return OK_PIXELS (window_box_left_offset (it->w, TEXT_AREA)
+                               + window_box_width (it->w, TEXT_AREA) / 2);
        }
 
       prop = buffer_local_value (prop, it->w->contents);
@@ -32207,6 +32218,8 @@ They are still logged to the *Messages* buffer.  */);
   DEFSYM (Qspace, "space");
   DEFSYM (Qmargin, "margin");
   DEFSYM (Qpointer, "pointer");
+  DEFSYM (Qleft_edge, "left-edge");
+  DEFSYM (Qright_edge, "right-edge");
   DEFSYM (Qleft_margin, "left-margin");
   DEFSYM (Qright_margin, "right-margin");
   DEFSYM (Qcenter, "center");