vga.c

#include "vga.h"
#include "common.h"

#define SCREEN_HEIGHT 25
#define SCREEN_WIDTH 80

static u16int* vga_mem;
static int cursor;

void vga_init()
{
	cursor = 0;

	if ((*((volatile u16int*) 0x410) & 0x30) == 0x30) // detecting monochrome monitor
		vga_mem = (u16int*) 0xB0000;
	else
		vga_mem = (u16int*) 0xB8000; // it's color
}

void vga_cls()
{
	int i;
	for (i = 0; i < SCREEN_WIDTH * SCREEN_HEIGHT;   i)
		*(vga_mem   i) = (u16int) 3872; // ((((0 << 4) | (15 & 0xFF)) << 8) | 0x20) // white spaces on black background
}

static void vga_scroll()
{
	int i;
	// rewrite lines one up
	for (i = 0; i < SCREEN_WIDTH * (SCREEN_HEIGHT - 1);   i)
		vga_mem[i] = vga_mem[i   SCREEN_WIDTH];

	// clear last line
	for(i = 0; i < SCREEN_WIDTH;   i)
		vga_mem[SCREEN_WIDTH * (SCREEN_HEIGHT - 1)   i] = 3872; // ((((0 << 4) | (15 & 0xFF)) << 8) | 0x20) // white spaces on black background
}

void vga_puts(const char* str)
{
	// white letters on black background
	const u16int attribute = 3840; // ((((0 << 4) | (15 & 0x0F)) << 8))

	int i = 0;
	while (str[i] != '\0')
	{
		if (cursor == SCREEN_WIDTH * SCREEN_HEIGHT)
		{
			vga_scroll();
			cursor = SCREEN_WIDTH * (SCREEN_HEIGHT - 1);
		}

		switch (str[i])
		{
		case '\n':
			cursor = cursor   80 - cursor % 80;
			break;
		case '\r':
			cursor = cursor - cursor % 80;
			break;
		case '\t':
			// increment to align to 8
			while ((cursor % 80) % 8 != 0)
				  cursor;
			break;
		default:
			vga_mem[cursor] = (u16int) (attribute | str[i]);
			  cursor;
		}

		  i;
	}
}