From: Ben Harris <bjh21@bjh21.me.uk>
Date: Thu, 2 Jan 2025 00:27:50 +0000 (+0000)
Subject: Add a comment explaining the purpose of aalt_overrides
X-Git-Tag: bedstead-3.251~47
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~bjharris/git?a=commitdiff_plain;h=ad5c57432161232497cf8856a5e3bb9a002e1b9c;p=bedstead.git

Add a comment explaining the purpose of aalt_overrides
---

diff --git a/bedstead.c b/bedstead.c
index e2410d6..1bfe8a5 100644
--- a/bedstead.c
+++ b/bedstead.c
@@ -2693,6 +2693,19 @@ static int const nglyphs = NGLYPHS;
 
 static struct glyph const *glyphs_by_name[NGLYPHS];
 
+/*
+ * This array defines 'aalt' mappings that should not be automatically
+ * generated from glyph names.  The OpenType specification says that
+ * different fonts in the same family should order the results of the
+ * 'aalt' lookup the same, which implies that applications might
+ * reasonably record the index of an alternative.  To avoid breaking
+ * such applications when Bedstead is upgraded, we want to ensure that
+ * any such indexes in an old version of a font still work in newer
+ * (minor) versions.  For most AlternateSets in the 'aalt' lookup,
+ * this will happen naturally, but where it doesn't, this table
+ * explicitly specifies the list of alternative glyphs so that they
+ * match older versions.
+ */
 #define MAX_ALT_SUB_OVERRIDE 3
 static struct alt_sub_override {
 	char const *base;
@@ -2701,12 +2714,12 @@ static struct alt_sub_override {
 	{ "D", { "D.c2sc", "D.serif", "D.narrow" } },
 	{ "J", { "J.c2sc", "J.narrow", "J.narrow" } },
 	{ "L", { "L.c2sc", "L.narrow", "L.narrow" } },
-	{ "ccedilla", { "ccedilla.angular", "ccedilla.sc" } }, // maybe not?
+	{ "ccedilla", { "ccedilla.angular", "ccedilla.sc" } },
 	{ "colon", { "colon.leftsmall", "colon.leftsmall" } },
-	{ "ocircumflex", { "ocircumflex.large", "ocircumflex.sc" } }, // maybe not?
+	{ "ocircumflex", { "ocircumflex.large", "ocircumflex.sc" } },
 	{ "question", { "question.open", "question.open" } },
 	{ "semicolon", { "semicolon.left", "semicolon.left" } },
-	{ "ugrave", { "ugrave.roundjoined", "ugrave.sc" } }, // maybe not?
+	{ "ugrave", { "ugrave.roundjoined", "ugrave.sc" } },
 };
 
 #define MAXSUBS 10