Function quantize_quadrant 

pub fn quantize_quadrant(pixels: [impl Into<Pixel>; 4]) -> Glyph

Posterizes a 2x2 pixel block ([top_left, top_right, bottom_left, bottom_right]) to one of the 16 quadrant block glyphs plus two representative colors.

Doubles both horizontal and vertical resolution over quantize_half_block.

On the bundled pixel backends (retroglyph-software, retroglyph-gl), rendering these glyphs correctly requires a font that actually declares coverage for the quadrant block characters: CP437 has no mapping for them. A font built with retroglyph_window‘s BitmapFont::new (CP437-only) renders every quadrant glyph as a solid block. Supply quadrant coverage by passing either a primary font or a BitmapFont::with_charset fallback in a FontChain to those backends’ font() builder method; the glyph then takes the cell’s foreground color, which a tileset sprite (the other way to draw a non-CP437 shape) does not.

See the 16_subcell_image example for quantize_quadrant in action: https://main.retroglyph.dev/examples/16_subcell_image/terminal/.

Examples

use retroglyph_core::symbols::quantize_quadrant;

let black = (0, 0, 0);
let white = (255, 255, 255);
let glyph = quantize_quadrant([black, white, black, black]);
assert_eq!(glyph.ch, '▝'); // top-right quadrant

See quantize_half_block for why this never panics.