legacy: print inverted question mark for nonprintable characters

legacy/firmware/CHANGELOG.md

@@ -9,6 +9,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Added
 
 ### Changed
+- Print inverted question mark for non-printable characters.
 
 ### Deprecated
 

legacy/gen/font.inc

@@ -93,4 +93,4 @@
 	/* 0x7c | */ (uint8_t *)"\x02\xff\xff",
 	/* 0x7d } */ (uint8_t *)"\x04\x82\xee\x7c\x10",
 	/* 0x7e ~ */ (uint8_t *)"\x04\x08\x10\x08\x10",
-	/* 0x7f _ */ (uint8_t *)"\x01\x00",
+	/* 0x7f _ */ (uint8_t *)"\x05\xff\xdf\xb5\xcf\xff",

legacy/gen/fontfixed.inc

@@ -93,4 +93,4 @@
 	/* 0x7c | */ (uint8_t *)"\x03\x00\xfe\x00",
 	/* 0x7d } */ (uint8_t *)"\x04\x82\xee\x7c\x10",
 	/* 0x7e ~ */ (uint8_t *)"\x05\x18\x20\x10\x08\x30",
-	/* 0x7f _ */ (uint8_t *)"\x01\x00",
+	/* 0x7f _ */ (uint8_t *)"\x05\xff\xdf\xb5\xcf\xff",

legacy/gen/strwidth.c

@@ -9,7 +9,7 @@ static inline char convert(char c) {
   if (c < 0x80) {
     return c;
   } else if (c >= 0xC0) {
-    return '_';
+    return 0x7f;
   } else {
     return '\0';
   }

legacy/oled.c

@@ -276,7 +276,7 @@ static uint8_t convert_char(const char a) {
   // non-printable ASCII character
   if (c < ' ') {
     last_was_utf8 = 0;
-    return '_';
+    return 0x7f;
   }
 
   // regular ASCII character
@@ -290,7 +290,7 @@ static uint8_t convert_char(const char a) {
   // bytes 11xxxxxx are first bytes of UTF-8 characters
   if (c >= 0xC0) {
     last_was_utf8 = 1;
-    return '_';
+    return 0x7f;
   }
 
   if (last_was_utf8) {
@@ -298,7 +298,7 @@ static uint8_t convert_char(const char a) {
     return 0;  // skip glyph
   } else {
     // ... or they are just non-printable ASCII characters
-    return '_';
+    return 0x7f;
   }
 
   return 0;