内核终端中的游标

Question

我正在编辑这个内核。它不支持游标。我写了超过25行，它显示不超过25，我不能上或下看到其余的。这是除主函数之外的全部代码。

uint8_t make_color(enum vga_color fg, enum vga_color bg) {
    return fg | bg << 4;}
    static const size_t VGA_WIDTH = 80;
    static const size_t VGA_HEIGHT = 25;

    uint16_t make_vgaentry(char c, uint8_t color) {
    uint16_t c16 = c;
    uint16_t color16 = color;
    return c16 | color16 << 8;}

    size_t strlen(const char* str) {
    size_t ret = 0;

    while ( str[ret] != 0 )
            ret++;
    return ret;}
    static const size_t VGA_WIDTH = 80;
    static const size_t VGA_HEIGHT = 25;

    size_t terminal_row;
    size_t terminal_column;
    uint8_t terminal_color;
    uint16_t* terminal_buffer;
    void terminal_initialize() {
    terminal_row = 0;
    terminal_column = 0;
    terminal_color = make_color(COLOR_LIGHT_GREY, COLOR_BLACK);
    terminal_buffer = (uint16_t*) 0xB8000;

    for (size_t y = 0; y < VGA_HEIGHT; y++) {
            for (size_t x = 0; x < VGA_WIDTH; x++) {
                    const size_t index = y * VGA_WIDTH + x;
                    terminal_buffer[index] = make_vgaentry(' ',
                                    terminal_color);
            }}}
void terminal_setcolor(uint8_t color) {
    terminal_color = color;
 }

 void terminal_putentryat(char c, uint8_t color, size_t x, size_t y) 
  {
    const size_t index = y * VGA_WIDTH + x;
    if(y>VGA_HEIGHT){
            size_t index = (VGA_HEIGHT - 1) * VGA_WIDTH;
            for(size_t x = 0; x < VGA_WIDTH; ++x)
    {
   terminal_buffer[index + x] = vga_entry(' ', terminal_color);
   }
    }
    else
    terminal_buffer[index] = make_vgaentry(c, color);}
    void terminal_putchar(char c) {
    terminal_putentryat(c, terminal_color, terminal_column, 
                   terminal_row);
    if (++terminal_column == VGA_WIDTH) {
            terminal_column = 0;
            if (++terminal_row == VGA_HEIGHT)
               terminal_row = 0;}
            else if (c == '\n')
    {
        terminal_row = terminal_row + 1;
        terminal_column = 0;
    }
    }
void terminal_writestring(const char* data) {
    size_t datalen = strlen(data);
    for (size_t i = 0; i < datalen; i++)
            terminal_putchar(data[i]);}

我需要像终点站那样滚动，一行行。

Answer 1

void terminal_scrollUp(void)
{
    for (size_t y = 1; y < VGA_HEIGHT; y++) 
    {
        for (size_t x = 0; x < VGA_WIDTH; x++) 
        {
            const size_t index = y * VGA_WIDTH + x;
            terminal_buffer[index - VGA_WIDTH] = terminal_buffer[index];
        }
    }
    for(size_t col = 0; col < VGA_WIDTH; col++)
    {
        terminal_putentryat(' ', terminal_color, col, VGA_HEIGHT - 1);
    }
}

void terminal_putchar(char c) 
{
    terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
    if (++terminal_column == VGA_WIDTH || c == '\n') 
    {
        terminal_column = 0;
        if(terminal_row == VGA_HEIGHT - 1)
        {
            terminal_scrollUp();
        }
        else
        {
            terminal_row++;
        }
    }
}

Answer 2

显示在屏幕上的文本直接从内存中取出。如果您移动该内存的内容，它将看起来像文本移动。

因此，如果您在将最后一行设置为所有零时，从第二行移动到最后一行(到显示内存的开头)，那么它将看起来像是滚动的。

类似于：

char *ptr_to_first_line = terminal_buffer;
char *ptr_to_second_line = terminal_buffer + VGA_WIDTH * 2;  // *2 because of the attribute byte
char *ptr_to_last_line = terminal_buffer + (VGA_WIDTH * 2) * (VGA_HEIGHT - 1); // -1 to get the beginning of the last line
char *ptr_to_end = terminal_buffer + VGA_WIDTH * 2 * VGA_HEIGHT;

// Move (copy, overlapping memory okay) the memory, making appear as it's scrolling
// This copies from the second line to the first line, the third line to the second line, etc.
memmove(ptr_to_first_line, ptr_to_second_line, ptr_to_end - ptr_to_second_line);

// Clear the last line so it appears empty
memset(ptr_to_last_line, 0, VGA_WIDTH * 2);

在此之后，您所要做的就是将光标放在最后一行的开头。