src/output/vga_character.c


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#include "vga_character.h"

__asm__(".code16gcc\n");

static short CURSOR_LOC = 0;
static char* HEX_CHARS = "0123456789abcdef";

void vga_graphics_write_str(char* str) {
  while(*str) {
    vga_graphics_write_with_attr(*str++, 7);
  }
}

void vga_graphics_write_with_attr(char value, char attr) {
  vga_graphics_write_at_offset(value, CURSOR_LOC++);
  vga_graphics_write_at_offset(attr, CURSOR_LOC++);
}

void vga_graphics_write(char value) {
  vga_graphics_write_at_offset(value, CURSOR_LOC);
  CURSOR_LOC += 2;
}

void vga_graphics_byte_hex(char value) {
  char low = value & 0x0f;
  char high = (value & 0xf0) >> 4;
  vga_graphics_write(HEX_CHARS[high]);
  vga_graphics_write(HEX_CHARS[low]);
}

void vga_graphics_write_at_offset(char value, short offset) {
  __asm__(
    "mov %0, %%al          \n"
    "mov %1, %%di          \n"
    "mov %%al, %%gs:(%%di) \n"
    : :"r"(value), "r"(offset) : "%ax", "%di");
}

void vga_graphics_clear() {
  int TERM_WIDTH = 80;
  int TERM_HEIGHT = 25;

  int i = 0;
  while(i < TERM_WIDTH * TERM_HEIGHT) {
    vga_graphics_write_with_attr(' ', 7);
    i++;
  }
  CURSOR_LOC = 0;
}