glyph serialization

kiln-tui/src/utils.rs

@@ -1,5 +1,4 @@
 use color::Rgba8;
-use kiln_core::cp437::tile_to_char;
 use kiln_core::glyph::Glyph;
 use ratatui::layout::Rect;
 use ratatui::prelude::Color;
@@ -14,15 +13,27 @@ pub fn rgba8_to_color(c: Rgba8) -> Color {
     Color::Rgb(c.r, c.g, c.b)
 }
 
-/// Converts a [`Glyph`] to a single-character styled [`Span`].
+/// The character this terminal front-end draws for `glyph`.
 ///
-/// The tile index is mapped to a CP437 character; fg and bg are both applied.
+/// A glyph carries its character directly, so this is almost the identity — the
+/// one case that needs handling is the transparent sentinel `'\0'`, which means
+/// "draw nothing". By the time a glyph reaches a renderer, `Board::glyph_at` has
+/// already exhausted its precedence chain, so there is nothing underneath left to
+/// reveal and the cell is simply blank. Writing the NUL through to the terminal
+/// buffer would emit an unprintable character instead.
+///
+/// How a sentinel looks on screen is a front-end decision, which is why this
+/// lives here rather than in kiln-core.
+pub fn glyph_char(glyph: Glyph) -> char {
+    if glyph.is_visible() { glyph.tile } else { ' ' }
+}
+
+/// Converts a [`Glyph`] to a single-character styled [`Span`], applying fg and bg.
 pub fn glyph_to_span(glyph: Glyph) -> Span<'static> {
-    let ch = tile_to_char(glyph.tile).to_string();
     let style = Style::default()
         .fg(rgba8_to_color(glyph.fg))
         .bg(rgba8_to_color(glyph.bg));
-    Span::styled(ch, style)
+    Span::styled(glyph_char(glyph).to_string(), style)
 }
 
 /// Returns true if two `Rect`s share at least one cell.