fb.c

#include "io.h"
#include "fb.h"

#define FRAMEBUFFER_ADDR 0x000B8000;
#define FB_WIDTH 80
#define FB_HEIGHT 25
#define TAB "  "

static unsigned int fb_pos_x = 0;
static unsigned int fb_pos_y = 0;

/**
 * fb_write_cell:
 * Writes a character with the given foreground and background to position i
 * within the frame buffer.
 * fb and bg must be between 0 and 15
 * i must be between 0 and 80*25 = 2000
 */
void fb_write_cell(short i, char c, unsigned char fg, unsigned char bg) {
    unsigned char *fb = (unsigned char*)FRAMEBUFFER_ADDR;
    fb[i * 2] = c;
    fb[i * 2 + 1] = ((bg & 0x0f) << 4) | (fg & 0x0f);
}

void fb_move_cursor(unsigned short pos) {
    outb(FB_COMMAND_PORT, FB_HIGH_BYTE_COMMAND);
    outb(FB_DATA_PORT, ((pos >> 8) & 0x00FF));
    outb(FB_COMMAND_PORT, FB_LOW_BYTE_COMMAND);
    outb(FB_DATA_PORT, pos & 0x00FF);
}

// move cursor to next line
//
void fb_newline() {
    if (fb_pos_y >= FB_HEIGHT-1)
        fb_shift_up();
    else
        fb_pos_y++;

    fb_pos_x = 0;
    fb_move_cursor(fb_pos_x + (fb_pos_y * FB_WIDTH));
}

// advances cursor forward one character
// if at end of line, wrap to next line
void fb_advance_pos() {
    if (fb_pos_x >= FB_WIDTH - 1)
        fb_newline();
    else
        fb_pos_x++;

    fb_move_cursor(fb_pos_x + (fb_pos_y * FB_WIDTH));
}

void fb_write(char *buf, unsigned int len) {
    unsigned int i;
    u16int pos;
    for (i = 0; i < len; i++) {
        char c = buf[i];
        if (c == '\n' || c == '\r') {
        fb_newline();
        } else if (c == '\t') {
            fb_write_str(TAB);
        } else {
        pos = fb_pos_x + (fb_pos_y * FB_WIDTH);
            fb_write_cell(pos, c, FB_WHITE, FB_BLACK);
            fb_advance_pos();
        }
    }
}

void fb_write_str(char *buf) {
    fb_write(buf, strlen(buf));
}

void fb_clear() {
    fb_pos_x = 0;
    fb_pos_y = 0;

    int i;
    for (i=0; i<FB_WIDTH*FB_HEIGHT; i++) {
        fb_write_cell(i, ' ', FB_WHITE, FB_BLACK);
    }
    fb_move_cursor(0);
}

void fb_clear_row(u8int row) {
    size_t i;
    for (i = 0; i < FB_WIDTH; i++) {
        fb_write_cell((row * FB_WIDTH)+i, ' ', FB_WHITE, FB_BLACK);
    }
}

void fb_shift_up() {
    // use 16-bits here because each cell is 16-bits wide
    // this makes the pointer arithmetic work out correctly here
    u16int *fb = (u16int*) FRAMEBUFFER_ADDR;
    memmove(fb, fb + FB_WIDTH, FB_WIDTH *2 * (FB_HEIGHT * 2 - 1));
    fb_clear_row(FB_HEIGHT - 1);
}

void fb_wrap_vertical() {
    fb_pos_y = 0;
    fb_clear_row(fb_pos_y);
    fb_move_cursor(0);
}