ableos/sysdata/libraries/render/src/text.hb

.{log, memory} := @use("../../stn/src/lib.hb")

PSF1Header := packed struct {
	magic: u16,
	font_mode: u8,
	character_size: u8,
}

PSF2Header := packed struct {
	magic: u32,
	version: u32,
	header_size: u32,
	flags: u32,
	num_glyph: u32,
	bytes_per_glyph: u32,
	height: u32,
	width: u32,
}

Font := struct {
	data: ^u8,
	width: uint,
	height: uint,
	num_glyphs: uint,
	bytes_per_glyph: uint,
	line_gap: uint,
	char_gap: uint,
	unicode: ?^u16,
}

font_from_psf1 := fn(psf: ^u8): ?Font {
	header := @as(^PSF1Header, @bitcast(psf))
	if header.magic != 0x436 {
		log.error("failed to load psf font: not a psf1 font, idiot\0")
		return null
	}

	psf += @sizeof(PSF1Header)

	return .(
		psf,
		8,
		header.character_size,
		256,
		header.character_size,
		0,
		0,
		null,
	)
}

font_from_psf2 := fn(psf: ^u8, unicode: bool): ?Font {
	header := @as(^PSF2Header, @bitcast(psf))
	if header.magic != 0x864AB572 {
		log.error("failed to load psf font: not a psf2 font, idiot\0")
		return null
	}

	psf += header.header_size

	font := Font.(
		psf,
		header.width,
		header.height,
		header.num_glyph,
		header.bytes_per_glyph,
		0,
		0,
		null,
	)
	if (header.flags & 1) != 0 & unicode {
		init_unicode(&font)
	}
	return font
}

get_glyph := fn(font: Font, index: u8): ^u8 {
	return font.data + @as(uint, index) * font.bytes_per_glyph
}

UNC_TABLE_SIZE := 1 << 16

init_unicode := fn(font: ^Font): void {
	font.unicode = memory.alloc(u16, UNC_TABLE_SIZE)

	@inline(memory.set, u16, &0xFFFF, font.unicode, UNC_TABLE_SIZE)

	table := font.data + font.num_glyphs * font.bytes_per_glyph
	curr_glyph := @as(u16, 0)

	loop if curr_glyph >= font.num_glyphs break else {
		loop {
			byte := *table
			table += 1

			if byte == 0xFF break
			if byte == 0xFE {
				continue
			}

			unicode := @as(uint, 0)
			bytes_to_read := @as(uint, 1)

			if (byte & 0x80) == 0 {
				unicode = byte
			} else if (byte & 0xE0) == 0xC0 {
				unicode = byte & 0x1F
				bytes_to_read = 2
			} else if (byte & 0xF0) == 0xE0 {
				unicode = byte & 0xF
				bytes_to_read = 3
			} else if (byte & 0xF8) == 0xF0 {
				unicode = byte & 0x7
				bytes_to_read = 4
			} else {
				continue
			}

			valid := true
			loop if bytes_to_read <= 1 break else {
				next_byte := *table
				if (next_byte & 0xC0) != 0x80 {
					valid = false
				}
				if valid == false {
					break
				}
				unicode = unicode << 6 | next_byte & 0x3F
				table += 1
				bytes_to_read -= 1
			}

			if valid == false continue

			if bytes_to_read == 4 {
				if unicode < 0x10000 | unicode > 0x10FFFF continue

				if unicode <= 0xFFFF {
					if unicode < UNC_TABLE_SIZE {
						*(@unwrap(font.unicode) + unicode) = curr_glyph
					}
				} else {
					unicode -= 0x10000
					high_surrogate := 0xD800 | unicode >> 10 & 0x3FF
					low_surrogate := 0xDC00 | unicode & 0x3FF

					if high_surrogate < UNC_TABLE_SIZE {
						*(@unwrap(font.unicode) + high_surrogate) = curr_glyph
					}
					if low_surrogate < UNC_TABLE_SIZE {
						*(@unwrap(font.unicode) + low_surrogate) = curr_glyph
					}
				}
			} else {
				if unicode < UNC_TABLE_SIZE {
					*(@unwrap(font.unicode) + unicode) = curr_glyph
				}
			}
		}
		curr_glyph += 1
	}
}