Function vga_debug_draw_glyph 

unsafe fn vga_debug_draw_glyph(
    fb: *mut u8,
    pitch: usize,
    x: usize,
    y: usize,
    ch: u8,
    fg: u32,
    bg: u32,
    bpp_bytes: usize,
)

Draw a single 8×16 character from the panic font.

First clears the entire cell with bg, then draws the glyph’s foreground pixels. This guarantees crisp, ghost-free text (like Linux fbcon).