blog_os/src/vga_buffer.rs

const BUFFER_HEIGHT: usize = 25;
const BUFFER_WIDTH: usize = 80;

#[macro_export]
macro_rules! print {
    ($($arg:tt)*) => ($crate::vga_buffer::_print(format_args!($($arg)*)));
}

#[macro_export]
macro_rules! println {
    ($fmt:expr) => (print!(concat!($fmt, "\n")));
    ($fmt:expr, $($arg:tt)*) => (print!(concat!($fmt, "\n"), $($arg)*));
}

pub fn clear_screen() {
    for _ in 0..BUFFER_HEIGHT {
        println!("");
    }
}

pub fn _print(fmt: ::core::fmt::Arguments) {
    use core::fmt::Write;
    static mut WRITER: Writer = Writer::new(Color::LightGreen, Color::Black);
    let _ = unsafe{WRITER.write_fmt(fmt)};
}

pub struct Writer {
    column_position: usize,
    color_code: ColorCode,
}

impl Writer {
    pub const fn new(foreground: Color, background: Color) -> Writer {
        Writer {
            column_position: 0,
            color_code: ColorCode::new(foreground, background),
        }
    }

    pub fn write_byte(&mut self, byte: u8) {
        const NEWLINE: u8 = b'\n';

        match byte {
            NEWLINE => self.new_line(),
            byte => {
                if self.column_position >= BUFFER_WIDTH {
                    self.new_line()
                }
                let row = BUFFER_HEIGHT - 1;
                let col = self.column_position;

                Self::buffer().chars[row][col] = ScreenChar {
                    ascii_character: byte,
                    color_code: self.color_code,
                };
                self.column_position += 1;
            }
        }
    }

    fn buffer() -> &'static mut Buffer {
        const BUFFER: *mut Buffer = 0xb8000 as *mut _;
        unsafe{&mut *BUFFER}
    }

    fn new_line(&mut self) {
        let buffer = Self::buffer();
        for row in 0..(BUFFER_HEIGHT-1) {
            buffer.chars[row] = buffer.chars[row + 1]
        }
        self.clear_row(BUFFER_HEIGHT-1);
        self.column_position = 0;
    }

    fn clear_row(&mut self, row: usize) {
        let blank = ScreenChar {
            ascii_character: ' ' as u8,
            color_code: self.color_code,
        };
        Self::buffer().chars[row] = [blank; BUFFER_WIDTH];
    }
}

impl ::core::fmt::Write for Writer {
    fn write_str(&mut self, s: &str) -> ::core::fmt::Result {
        for byte in s.bytes() {
          self.write_byte(byte)
        }
        Ok(())
    }
}

#[derive(Clone, Copy)]
#[allow(dead_code)]
#[repr(u8)]
pub enum Color {
    Black      = 0,
    Blue       = 1,
    Green      = 2,
    Cyan       = 3,
    Red        = 4,
    Magenta    = 5,
    Brown      = 6,
    LightGray  = 7,
    DarkGray   = 8,
    LightBlue  = 9,
    LightGreen = 10,
    LightCyan  = 11,
    LightRed   = 12,
    Pink       = 13,
    Yellow     = 14,
    White      = 15,
}

#[derive(Clone, Copy)]
struct ColorCode(u8);

impl ColorCode {
    const fn new(foreground: Color, background: Color) -> ColorCode {
        ColorCode((background as u8) << 4 | (foreground as u8))
    }
}

#[derive(Clone, Copy)]
#[repr(packed)]
struct ScreenChar {
    ascii_character: u8,
    color_code: ColorCode,
}

struct Buffer {
    chars: [[ScreenChar; BUFFER_WIDTH]; BUFFER_HEIGHT],
}