pub const SHADE_LEVELS: [char; 5];Expand description
The five bar levels from empty to full, indexed 0..=4: a blank cell, then LIGHT_SHADE,
MEDIUM_SHADE, DARK_SHADE, and FULL in order.
Every glyph here is in CP437 (verified against CP437_TO_UNICODE in retroglyph-window),
unlike NINE_LEVELS: a caller drawing through a pixel backend that resolves glyphs via a
CP437 table, or a tileset/sprite backend that can’t tint an arbitrary glyph by Style::fg,
can use this ramp and still get five distinguishable fill levels instead of collapsing to a
single fallback block. Index it by round(fraction * 4.0) as usize for one bar column.