From: Neil Williamson <neil.williamson@gmail.com>
Date: Mon, 25 Nov 2024 00:14:52 +0000 (+0000)
Subject: Correct separated vs contiguous flag in ZVBI compat mappings
X-Git-Tag: bedstead-3.251~93
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~bjharris/git?a=commitdiff_plain;h=69166f263937481e0ea5feac62fb07323b8d7d0d;p=bedstead.git

Correct separated vs contiguous flag in ZVBI compat mappings

[ from email ]

One thing I wanted to query was the ZVBI mosaic graphics codepoints at
0xEE00 to 0xEE7F.  The ZVBI code says (in lang.c):

" Table 47 G1 Block Mosaic is not representable
* in Unicode, translated to private code U+EE00 ... U+EE7F.
* (contiguous form has bit 5 set, separate form cleared)."

My reading of this is that the separated forms should therefore sit at
0xEE00-0xEE1F and 0xEE40-0xEE5F, with the contiguous forms at 0xEE20-0xEE3F
and 0xEE60-0xEE7F.  This is indeed what the teletext1/2/4 fonts commonly
seen in teletext recoveries do; see for example
https://al.zerostem.io/~al/teletext/bbc1/1996-12-28-0008.1/100.html.
Bedstead maps these the opposite way around, however, and if you swap it in
on the linked page, all the contiguous and separated mosaics will swap
places.
---

diff --git a/bedstead.c b/bedstead.c
index f6eaba0..1fb5e81 100644
--- a/bedstead.c
+++ b/bedstead.c
@@ -2374,7 +2374,7 @@ static struct glyph {
  /* Private use area */
  /* U+EE00--U+EE7F: zvbi mosaic graphics */
 #define M(x) {{(0x##x & 0x1f)|((0x##x & 0x40)>>1)}, U(EE##x), \
-	      (0x##x & 0x20 ? SEP6 : MOS6)}
+	      (0x##x & 0x20 ? MOS6 : SEP6)}
  M(00), M(01), M(02), M(03), M(04), M(05), M(06), M(07),
  M(08), M(09), M(0A), M(0B), M(0C), M(0D), M(0E), M(0F),
  M(10), M(11), M(12), M(13), M(14), M(15), M(16), M(17),