From: Gerd Möllmann <gerd@gnu.org>
Date: Tue, 21 Jan 2025 19:40:19 +0000 (+0100)
Subject: Improve copying current glyphs when building frame matrix
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=830cb0d17ad09dd0e1f8bc2b508403deb6dc7495;p=emacs.git

Improve copying current glyphs when building frame matrix

* src/dispnew.c (build_frame_matrix_from_leaf_window): Don't make space
glyphs. More comments.

(cherry picked from commit d30f40868bf260692c7702e43b439d592b830e16)
---

diff --git a/src/dispnew.c b/src/dispnew.c
index ff413fab574..b65f0c1c62a 100644
--- a/src/dispnew.c
+++ b/src/dispnew.c
@@ -2624,22 +2624,27 @@ build_frame_matrix_from_leaf_window (struct glyph_matrix *frame_matrix, struct w
 	  current_row_p = 1;
 	}
 
+      /* If someone asks why we are copying current glyphs here, and
+	 maybe never enable the desired frame row we copy to:
+
+	 - there might be a window to the right of this one that has a
+	   corresponding desired window row.
+	 - we need the complete frame row for scrolling.  */
       if (current_row_p)
 	{
-	  /* If the desired glyphs for this row haven't been built,
-	     copy from the corresponding current row, but only if it
-	     is enabled, because ottherwise its contents are invalid.  */
+	  /* If the desired glyphs for this row haven't been built, copy
+	     from the corresponding current row. If that row is not
+	     enabled, its contents might be invalid.  Make sure that
+	     glyphs have valid frames set in that case.  This is closer
+	     to what we did before child frames were added, and seems to
+	     be something tty redisplay implicitly relies on.  */
 	  struct glyph *to = frame_row->glyphs[TEXT_AREA] + window_matrix->matrix_x;
 	  struct glyph *from = window_row->glyphs[0];
 	  for (int i = 0; i < window_matrix->matrix_w; ++i)
 	    {
-	      if (window_row->enabled_p)
-		to[i] = from[i];
-	      else
-		{
-		  to[i] = space_glyph;
-		  to[i].frame = f;
-		}
+	      to[i] = from[i];
+	      if (!window_row->enabled_p)
+		to[i].frame = f;
 	    }
 	}
       else