Consider changing the `brightblack` color and glyph of NULL bytes

[bitraid]

I have a couple of issues with the display of the offset and NULL bytes. They are not such a big deal for me, because I do a manual build and I apply a patch to fix them, but I thought of bringing them up anyway, for the benefit of other users with similar terminal configurations.

• The first one, involves the color. brightblack is the background color of the Solarized Dark color scheme, so it becomes invisible on terminals with that configuration. This is a very popular color scheme, and I’m surprised that it hasn’t been brought up already. I would suggest to be changed to blue, which is a more compatible foreground color, and it’s not used for something else.

• The second, has to do with the choice of the display character for NULL bytes. The "diamond operator" (U+22C4) is not a very common symbol, and it's not present in some popular fonts, like Terminus and Adobe Source Code Pro, so a fallback font is used and it doesn’t look nice. I think a better choice would be a more common symbol, like "subscript zero" (U+2080).

[sharkdp]

Sounds reasonable, thank you. How does that look like (for different terminal schemes)?

[bitraid]

Thanks.

I took a few screenshots of foot terminal, showcasing 8 color schemes and 3 fonts:

• Solarized Dark, Terminus

• Solarized Light, Terminus

• Dracula, Source Code Pro

• Gruvbox Dark, Source Code Pro

• Gruvbox Light, Source Code Pro

• Monokai Pro, Nimbus Mono

• Nord, Nimbus Mono

• XTerm, Nimbus Mono

I applied this patch (doesn't include the test change):

diff --git a/src/colors.rs b/src/colors.rs
index b76e641..eb5ea0a 100644
--- a/src/colors.rs
+++ b/src/colors.rs
@@ -1,7 +1,7 @@
 use owo_colors::{colors, Color};
 
-pub const COLOR_NULL: &[u8] = colors::BrightBlack::ANSI_FG.as_bytes();
-pub const COLOR_OFFSET: &[u8] = colors::BrightBlack::ANSI_FG.as_bytes();
+pub const COLOR_NULL: &[u8] = colors::Blue::ANSI_FG.as_bytes();
+pub const COLOR_OFFSET: &[u8] = colors::Blue::ANSI_FG.as_bytes();
 pub const COLOR_ASCII_PRINTABLE: &[u8] = colors::Cyan::ANSI_FG.as_bytes();
 pub const COLOR_ASCII_WHITESPACE: &[u8] = colors::Green::ANSI_FG.as_bytes();
 pub const COLOR_ASCII_OTHER: &[u8] = colors::Green::ANSI_FG.as_bytes();
@@ -24,12 +24,12 @@ pub const CP437: [char; 256] = [
     // ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
     // OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
     //
-    // modified to use the ⋄ character instead of ␀
+    // modified to use the ₀ character instead of ␀
 
     // use https://en.wikipedia.org/w/index.php?title=Code_page_437&oldid=978947122
     // not ftp://ftp.unicode.org/Public/MAPPINGS/VENDORS/MICSFT/PC/CP437.TXT
     // because we want the graphic versions of 01h–1Fh + 7Fh
-    '⋄','☺','☻','♥','♦','♣','♠','•','◘','○','◙','♂','♀','♪','♫','☼',
+    '₀','☺','☻','♥','♦','♣','♠','•','◘','○','◙','♂','♀','♪','♫','☼',
     '►','◄','↕','‼','¶','§','▬','↨','↑','↓','→','←','∟','↔','▲','▼',
     ' ','!','"','#','$','%','&','\'','(',')','*','+',',','-','.','/',
     '0','1','2','3','4','5','6','7','8','9',':',';','<','=','>','?',
diff --git a/src/lib.rs b/src/lib.rs
index bae2945..10d6b81 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -27,7 +27,7 @@ pub enum ByteCategory {
 #[derive(Copy, Clone, Debug, Default, ValueEnum)]
 #[non_exhaustive]
 pub enum CharacterTable {
-    /// Show printable ASCII characters as-is, '⋄' for NULL bytes, ' ' for
+    /// Show printable ASCII characters as-is, '₀' for NULL bytes, ' ' for
     /// space, '_' for other ASCII whitespace, '•' for other ASCII characters,
     /// and '×' for non-ASCII bytes.
     #[default]
@@ -96,7 +96,7 @@ impl Byte {
         use crate::ByteCategory::*;
         match character_table {
             CharacterTable::Default => match self.category() {
-                Null => '⋄',
+                Null => '₀',
                 AsciiPrintable => self.0 as char,
                 AsciiWhitespace if self.0 == 0x20 => ' ',
                 AsciiWhitespace => '_',
diff --git a/src/main.rs b/src/main.rs
index 2e32cff..eef9dd8 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -494,7 +494,7 @@ fn print_color_table() -> io::Result<()> {
 
     // NULL bytes
     stdout.write_all(COLOR_NULL)?;
-    writeln!(stdout, "⋄ NULL bytes (0x00)")?;
+    writeln!(stdout, "₀ NULL bytes (0x00)")?;
     stdout.write_all(COLOR_RESET)?;
 
     // ASCII printable

[sharkdp]

I really like how brightblack makes the zero characters fade into the background on my current terminal scheme:

But it obviously looks very bad on other terminal schemes. It vanishes for solarized dark, as you mentioned. And it has high contrast (which is the opposite of what I'd like to have) for light color themes.

I think the only reasonable way forward is to add themes, even if don't really want to. Maybe we can start with something like dark (auto), light, high-contrast to begin with? Or maybe it would be better to let users control single colors, as in --set-color null <ansi code>?

[bitraid]

I like the idea of having the option to set each color. There aren't many items to configure anyway (maybe include the border, too). Even better would be to also have the option for setting the glyph of each non-printable character type.

[sharkdp]

I'm also okay with changing the 0 character without making it configurable, for now. I'm not sure I like subscript 0. It's not vertically centered and looks a bit off.

[bitraid]

I'm not a big fan of it, either - I chose it mostly because it looks like 0. I recently switched to U+2027 ("hyphenation point" ‧ - it is a little thicker than middle dot).