Support cons cell for 'line-spacing'

* etc/NEWS: Announce the change.
* src/dispextern.h (struct glyph_row): Add
'extra_line_spacing_above' member.
(struct it): Add 'extra_line_spacing_above' member.
* src/frame.h (struct frame): Add 'extra_line_spacing_above'
member.  Update comment for 'extra_line_spacing.'
* src/buffer.c (syms_of_buffer): Update the docstring of
'line-spacing' to describe the cons cell usage.
* src/buffer.h (struct buffer): Update comment for
'extra_line_spacing'.
* src/frame.c (gui_set_line_spacing): Handle cons cell value for
'line-spacing'.  Calculate and set 'extra_line_spacing_above'
for both integer and float pairs.
* src/xdisp.c (init_iterator): Initialize 'extra_line_spacing_above'
from buffer or frame 'line-spacing', handling cons cells for both
integer and float values.
(gui_produce_glyphs): Use 'extra_line_spacing_above' to distribute
spacing between ascent and descent.  Update 'max_extra_line_spacing'
calculation.
(resize_mini_window): Take line spacing into account when resizing the
mini window.  Pass height of a single line to 'grow_mini_window' and
'shrink_mini_window'.
* src/window.c (grow_mini_window, shrink_mini_window): Add unit
argument which defines height of a single line.
* src/window.h (grow_mini_window, shrink_mini_window): Adjust function
prototypes accordingly with unit argument.
* lisp/subr.el (total-line-spacing): New function to calculate total
spacing from a number or cons cell.
(posn-col-row): Use total-line-spacing.
* lisp/simple.el (default-line-height): Use 'total-line-spacing'.
* lisp/textmodes/picture.el (picture-mouse-set-point): Use
'total-line-spacing'.
* lisp/window.el (window-default-line-height): Use
'total-line-spacing'.
(window--resize-mini-window): Take 'line-spacing' into account.
* test/lisp/subr-tests.el (total-line-spacing): New test.
* test/src/buffer-tests.el (test-line-spacing): New test.
* doc/emacs/display.texi (Display Custom): Document that
'line-spacing' can be a cons cell.
(Line Height): Document the new cons cell format for 'line-spacing'
to allow vertical centering.

Co-authored-by: Przemysław Alexander Kamiński <alexander@kaminski.se>
Co-authored-by: Daniel Mendler <mail@daniel-mendler.de>

1 files changed, 7 insertions, 8 deletions

diff --git a/src/window.c b/src/window.c
index 497c587b167..c4f2e4e491f 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5894,11 +5894,11 @@ resize_mini_window_apply (struct window *w, int delta)
  * line of text.
  */
 void
-grow_mini_window (struct window *w, int delta)
+grow_mini_window (struct window *w, int delta, int unit)
 {
   struct frame *f = XFRAME (w->frame);
   int old_height = window_body_height (w, WINDOW_BODY_IN_PIXELS);
-  int min_height = FRAME_LINE_HEIGHT (f);
+  int min_height = unit;
 
   eassert (MINI_WINDOW_P (w));
 
@@ -5926,7 +5926,7 @@ grow_mini_window (struct window *w, int delta)
         resize_mini_window_apply (w, -XFIXNUM (grow));
     }
   FRAME_WINDOWS_FROZEN (f)
-    = window_body_height (w, WINDOW_BODY_IN_PIXELS) > FRAME_LINE_HEIGHT (f);
+    = window_body_height (w, WINDOW_BODY_IN_PIXELS) > unit;
 }
 
 /**
@@ -5936,11 +5936,10 @@ grow_mini_window (struct window *w, int delta)
  * line of text.
  */
 void
-shrink_mini_window (struct window *w)
+shrink_mini_window (struct window *w, int unit)
 {
   struct frame *f = XFRAME (w->frame);
-  int delta = (window_body_height (w, WINDOW_BODY_IN_PIXELS)
-               - FRAME_LINE_HEIGHT (f));
+  int delta = (window_body_height (w, WINDOW_BODY_IN_PIXELS) - unit);
 
   eassert (MINI_WINDOW_P (w));
 
@@ -5959,10 +5958,10 @@ shrink_mini_window (struct window *w)
   else if (delta < 0)
     /* delta can be less than zero after adding horizontal scroll
        bar.  */
-    grow_mini_window (w, -delta);
+    grow_mini_window (w, -delta, unit);
 
   FRAME_WINDOWS_FROZEN (f)
-    = window_body_height (w, WINDOW_BODY_IN_PIXELS) > FRAME_LINE_HEIGHT (f);
+    = window_body_height (w, WINDOW_BODY_IN_PIXELS) > unit;
 }
 
 DEFUN ("resize-mini-window-internal", Fresize_mini_window_internal,