0187-实现换行输出

环境

• Time 2022-11-13
• WSL-Ubuntu 22.04
• QEMU 6.2.0
• Rust 1.67.0-nightly
• VSCode 1.73.1

前言

说明

参考：https://os.phil-opp.com/vga-text-mode

目标

使用 VGA 输出的时候，在一行已经满的情况下，自动换行输出。

易失操作

对于输出到屏幕，为了避免编译器优化，需要增加一个副作用。

volatile 依赖

[dependencies]
volatile = "0.2.6"

修改 Buffer 定义

use volatile::Volatile;

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

修改输出定义

impl Writer {
    pub fn write_byte(&mut self, byte: u8) {
        match byte {
            b'\n' => self.new_line(),
            byte => {
                ...

                self.buffer.chars[row][col].write(ScreenChar {
                    ascii_character: byte,
                    color_code: color_code,
                });
                ...
            }
        }
    }
    ...
}

格式化宏

write! 宏

use core::fmt;

impl fmt::Write for Writer {
    fn write_str(&mut self, s: &str) -> fmt::Result {
        self.write_string(s);
        Ok(())
    }
}

输出验证

pub fn print_something() {
    use core::fmt::Write;
    let mut writer = Writer {
        column_position: 0,
        color_code: ColorCode::new(Color::Yellow, Color::Black),
        buffer: unsafe { &mut *(0xb8000 as *mut Buffer) },
    };

    writer.write_byte(b'H');
    writer.write_string("ello! ");
    write!(writer, "The numbers are {} and {}", 42, 1.0/3.0).unwrap();
}

换行

新一行

    fn new_line(&mut self) {
        for row in 1..BUFFER_HEIGHT {
            for col in 0..BUFFER_WIDTH {
                let character = self.buffer.chars[row][col].read();
                self.buffer.chars[row - 1][col].write(character);
            }
        }
        self.clear_row(BUFFER_HEIGHT - 1);
        self.column_position = 0;
    }

清除行

    fn clear_row(&mut self, row: usize) {
        let blank = ScreenChar {
            ascii_character: b' ',
            color_code: self.color_code,
        };
        for col in 0..BUFFER_WIDTH {
            self.buffer.chars[row][col].write(blank);
        }
    }

总结

实现了向屏幕输出时，如果一行已满，则另起一行。

附录