99 lines
3.1 KiB
Rust
99 lines
3.1 KiB
Rust
use core::ptr::write_volatile;
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/// VGA text mode display dimensions.
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///
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/// The standard VGA text mode provides an 80×25 grid of character cells.
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/// Each cell is 2 bytes: [ASCII byte] [attribute byte].
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/// The buffer starts at physical address 0xB8000 and is memory-mapped into
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/// the CPU's address space. The x86_64 bootloader identity-maps this region,
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/// so we can write to it with regular memory stores — but we must use volatile
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/// writes to prevent the compiler from optimizing away MMIO operations.
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pub const VGA_ADDR: *mut u8 = 0xB8000 as *mut u8;
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pub const WIDTH: usize = 80;
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pub const HEIGHT: usize = 25;
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/// Standard VGA text-mode colors.
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///
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/// The attribute byte layout:
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/// bits 0-3: foreground color (0 = black, 15 = white)
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/// bits 4-6: background color (0-7, hardware limit; bit 7 = blink)
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#[allow(dead_code)]
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#[repr(u8)]
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#[derive(Clone, Copy, Debug)]
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pub enum Color {
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Black = 0,
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Blue = 1,
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Green = 2,
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Cyan = 3,
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Red = 4,
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Magenta = 5,
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Brown = 6,
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LightGray = 7,
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DarkGray = 8,
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LightBlue = 9,
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LightGreen = 10,
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LightCyan = 11,
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LightRed = 12,
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Pink = 13,
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Yellow = 14,
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White = 15,
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}
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/// A packed attribute byte encoding foreground + background color.
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#[derive(Clone, Copy)]
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pub struct ColorCode(u8);
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impl ColorCode {
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/// Constructs a color code from foreground and background colors.
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///
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/// ## Hardware note
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/// The VGA attribute byte stores the background color in bits 4-6 (3 bits,
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/// limiting backgrounds to 0-7). Bit 7 is the blink enable bit, which we
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/// keep cleared. The foreground color uses bits 0-3 (including intensity
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/// on bit 3), giving 16 possible foreground colors.
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pub const fn new(fg: Color, bg: Color) -> ColorCode {
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ColorCode(((bg as u8) << 4) | (fg as u8))
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}
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}
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/// Clears the entire VGA screen to the given background color.
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///
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/// Writes a space character (0x20) with the appropriate attribute byte
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/// to every cell on the screen.
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pub fn clear_screen(bg: Color) {
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let color = ColorCode::new(Color::White, bg);
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for offset in (0..(WIDTH * HEIGHT * 2)).step_by(2) {
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unsafe {
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write_volatile(VGA_ADDR.add(offset), b' ');
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write_volatile(VGA_ADDR.add(offset + 1), color.0);
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}
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}
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}
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/// Writes a single character at position (row, col) with the given color.
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///
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/// The position is bounds-checked against the 80×25 screen. Writes outside
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/// the visible area are silently ignored.
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pub fn write_char(row: usize, col: usize, ch: u8, color: ColorCode) {
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if row < HEIGHT && col < WIDTH {
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let offset = (row * WIDTH + col) * 2;
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unsafe {
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write_volatile(VGA_ADDR.add(offset), ch);
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write_volatile(VGA_ADDR.add(offset + 1), color.0);
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}
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}
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}
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/// Writes a string starting at position (row, col) with the given color.
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///
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/// Stops at the right edge of the screen to avoid wrapping.
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pub fn write_str(row: usize, col: usize, s: &str, color: ColorCode) {
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for (i, &ch) in s.as_bytes().iter().enumerate() {
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if col + i < WIDTH {
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write_char(row, col + i, ch, color);
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} else {
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break;
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}
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}
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}
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