modules/overlays/emacs: Patch to make window dividers transparent

From https://github.com/djeis97/emacs/tree/transparency, modified to apply on
current Emacs.

2 files changed, 114 insertions, 0 deletions

diff --git a/modules/overlays/emacs-alpha-dividers.patch b/modules/overlays/emacs-alpha-dividers.patch
new file mode 100644
index 0000000..1246e89
--- /dev/null
+++ b/modules/overlays/emacs-alpha-dividers.patch
@@ -0,0 +1,113 @@
+--- a/src/xterm.c	1969-12-31 18:00:01.000000000 -0600
++++ a/src/xterm.c	2025-10-23 21:31:03.245064218 -0500
+@@ -7460,69 +7460,32 @@
+ #endif
+ }
+
++
++static void
++x_fill_rectangle_transp (struct frame *f, int x, int y, int width, int height)
++{
++#ifdef USE_CAIRO
++  Display *dpy = FRAME_X_DISPLAY (f);
++  cairo_t *cr;
++
++  cr = x_begin_cr_clip (f, f->output_data.x->normal_gc);
++  cairo_set_source_rgba(cr, 1, 1, 1, 0);
++  cairo_set_operator(cr, CAIRO_OPERATOR_SOURCE);
++  cairo_rectangle (cr, x, y, width, height);
++  cairo_fill (cr);
++  x_end_cr_clip (f);
++#endif
++}
++
++
+ /* Draw a window divider from (x0,y0) to (x1,y1)  */
+
+ static void
+ x_draw_window_divider (struct window *w, int x0, int x1, int y0, int y1)
+ {
+   struct frame *f = XFRAME (WINDOW_FRAME (w));
+-  struct face *face = FACE_FROM_ID_OR_NULL (f, WINDOW_DIVIDER_FACE_ID);
+-  struct face *face_first
+-    = FACE_FROM_ID_OR_NULL (f, WINDOW_DIVIDER_FIRST_PIXEL_FACE_ID);
+-  struct face *face_last
+-    = FACE_FROM_ID_OR_NULL (f, WINDOW_DIVIDER_LAST_PIXEL_FACE_ID);
+-  unsigned long color = face ? face->foreground : FRAME_FOREGROUND_PIXEL (f);
+-  unsigned long color_first = (face_first
+-			       ? face_first->foreground
+-			       : FRAME_FOREGROUND_PIXEL (f));
+-  unsigned long color_last = (face_last
+-			      ? face_last->foreground
+-			      : FRAME_FOREGROUND_PIXEL (f));
+-  Display *display = FRAME_X_DISPLAY (f);
+-
+-  if ((y1 - y0 > x1 - x0) && (x1 - x0 >= 3))
+-    /* A vertical divider, at least three pixels wide: Draw first and
+-       last pixels differently.  */
+-    {
+-      XSetForeground (display, f->output_data.x->normal_gc, color_first);
+-      x_fill_rectangle (f, f->output_data.x->normal_gc,
+-			x0, y0, 1, y1 - y0,
+-                        f->borders_respect_alpha_background);
+-      XSetForeground (display, f->output_data.x->normal_gc, color);
+-      x_fill_rectangle (f, f->output_data.x->normal_gc,
+-			x0 + 1, y0, x1 - x0 - 2, y1 - y0,
+-                        f->borders_respect_alpha_background);
+-      XSetForeground (display, f->output_data.x->normal_gc, color_last);
+-      x_fill_rectangle (f, f->output_data.x->normal_gc,
+-			x1 - 1, y0, 1, y1 - y0,
+-                        f->borders_respect_alpha_background);
+-    }
+-  else if ((x1 - x0 > y1 - y0) && (y1 - y0 >= 3))
+-    /* A horizontal divider, at least three pixels high: Draw first and
+-       last pixels differently.  */
+-    {
+-      XSetForeground (display, f->output_data.x->normal_gc, color_first);
+-      x_fill_rectangle (f, f->output_data.x->normal_gc,
+-			x0, y0, x1 - x0, 1,
+-                        f->borders_respect_alpha_background);
+-      XSetForeground (display, f->output_data.x->normal_gc, color);
+-      x_fill_rectangle (f, f->output_data.x->normal_gc,
+-			x0, y0 + 1, x1 - x0, y1 - y0 - 2,
+-                        f->borders_respect_alpha_background);
+-      XSetForeground (display, f->output_data.x->normal_gc, color_last);
+-      x_fill_rectangle (f, f->output_data.x->normal_gc,
+-			x0, y1 - 1, x1 - x0, 1,
+-                        f->borders_respect_alpha_background);
+-    }
+-  else
+-    {
+-    /* In any other case do not draw the first and last pixels
+-       differently.  */
+-      XSetForeground (display, f->output_data.x->normal_gc, color);
+-      x_fill_rectangle (f, f->output_data.x->normal_gc,
+-			x0, y0, x1 - x0, y1 - y0,
+-                        f->borders_respect_alpha_background);
+-    }
++
++  x_fill_rectangle_transp(f, x0, y0, x1-x0, y1-y0);
+ }
+
+ #ifdef HAVE_XDBE
+@@ -7722,15 +7685,11 @@
+ 	  GC gc = f->output_data.x->normal_gc;
+
+ 	  XSetForeground (display, gc, color);
+-	  x_fill_rectangle (f, gc, 0, margin, width, border,
+-                            f->borders_respect_alpha_background);
+-	  x_fill_rectangle (f, gc, 0, 0, border, height,
+-                            f->borders_respect_alpha_background);
+-	  x_fill_rectangle (f, gc, width - border, 0, border, height,
+-                            f->borders_respect_alpha_background);
+-	  x_fill_rectangle (f, gc, 0, height - bottom_margin - border,
+-			    width, border,
+-                            f->borders_respect_alpha_background);
++	  x_fill_rectangle_transp (f, 0, margin, width, border);
++	  x_fill_rectangle_transp (f, 0, 0, border, height);
++	  x_fill_rectangle_transp (f, width - border, 0, border, height);
++	  x_fill_rectangle_transp (f, 0, height - bottom_margin - border,
++			           width, border);
+ 	  XSetForeground (display, gc, FRAME_FOREGROUND_PIXEL (f));
+ 	}
+       else
diff --git a/modules/overlays/emacs.nix b/modules/overlays/emacs.nix
index b94b13b..da7cc0e 100644
--- a/modules/overlays/emacs.nix
+++ b/modules/overlays/emacs.nix
@@ -10,6 +10,7 @@ final: prev: {
       ["--with-x-toolkit=lucid" "--with-toolkit-scroll-bars"])
       configureFlags ++ ["--with-x-toolkit=no" "--without-toolkit-scroll-bars"];
     version = "31.0.50";
+    patches = patches ++ [./emacs-alpha-dividers.patch];
     src = prev.fetchFromSavannah {
       repo = "emacs";
       rev = "ce7f2b93bb4dc17ae083ca33327c618a2038f420";