OSDev.org

Code: Select all

; boot.asm
MODE_TYPE   equ  0
WIDTH       equ  640
HEIGHT      equ  480
DEPTH       equ  16

Code: Select all

int x_ = 0, y_ = font.Height;

void putpixel(int x, int y, int color) {
    unsigned char* screen = (unsigned char*) 0xA0000;
    // Hard-coded
    unsigned where = x*2 + y*1280;
    screen[where] = color & 255;              // BLUE
    screen[where + 1] = (color >> 8) & 255;   // GREEN
    screen[where + 2] = (color >> 16) & 255;  // RED
}

unsigned char reverse(unsigned char b) {
   b = (b & 0xF0) >> 4 | (b & 0x0F) << 4;
   b = (b & 0xCC) >> 2 | (b & 0x33) << 2;
   b = (b & 0xAA) >> 1 | (b & 0x55) << 1;
   return b;
}

void drawchar(char c, int x, int y, int fgcolor, int bgcolor)
{
	int cx, cy;
	int mask[8]={1,2,4,8,16,32,64,128};
        // Font layout starts from space (ascii 32)
        // Skip first character
	const unsigned char *glyph = font.Bitmap + ((int)c - 32 + 1) * font.Height;
 
	for(cy = 0; cy < font.Height; cy++){
		for(cx = 0; cx < font.Width; cx++) {
                        // For some reason it draws the glyphs backwards
			putpixel(x + cx, y + cy - 12, reverse(glyph[cy]) & mask[cx] ? fgcolor : bgcolor);
		}
	}
	x_ += font.Width;
	if (x_ >= 640)
	{
		x_ = 0;
		y_ += font.Height;
	}	
}

void drawchar(char c)
{
	drawchar(c, x_, y_, 0xFFFFFF, 0xAAAAAA);
}

void drawstring(int x, int y, const char* input)
{
	char buffer[strlen(input) + 1];
	memcpy(buffer, input, strlen(input)+1);

	char * ptr = buffer;
	while (*ptr)
	{
		if (*ptr == '\n')
		{
			x = 0;
			y += font.Height;
			x_ = x;
			y_ = y;
		} else {
			drawchar(*ptr, x, y, 0xFFFFFF, 0xAAAAAA);
			x += font.Width;
		}
		++ptr;
	}
}

void drawstring(const char* input)
{
	drawstring(x_, y_, input);
}